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Effects of drought on birds in the Kalahari, BotswanaMarc HerremansPublished online: 12 Nov 2009.

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Ostrich 2004, 75(4): 217–227Printed in South Africa — All rights reserved

Copyright © NISC Pty Ltd

OSTRICHISSN 0030–6525

Effects of drought on birds in the Kalahari, Botswana

Marc HerremansNatuurpunt Studie, Kardinaal Mercierplein 1, 2300 Mechelen, Belgium

e-mail: marc.herremans@natuurpunt.be

Results are presented from point-counts at six sites in the Kalahari in Botswana. Counts were repeated three times: during adry season following good rains (1991), during the next wet season when rains were far below average, and the following dryseason (1992) when the area became drought-stricken. Compared to the wet season, bird numbers decreased during thedrought by 37–81% and species by 8–52%; compared to the previous dry season, birds decreased by 5–71% and species by2–47%. Bird diversity (relative to numbers) tended to increase during the wet season but was little affected by drought, exceptin the northern Kalahari, where a greater proportion of birds moved out in response to drought. This gave the northern Kalaharithe most distinct bird community during a wet cycle, but it became again typically Kalahari during the drought. Thus, the typ-ical Kalahari bird communities expanded their range during drought into the moister periphery. Changes in numbers, mostprobably resulting from (local) movements were found in many species. Most confirmed earlier reports on their nomadic naturebut some, like Red-crested Lophotis ruficrista and Northern Black Afrotis afraoides Korhaan, Chestnut-vented Tit-BabblerParisoma subcaeruleum, Ant-eating Chat Myrmecocichla formicivora, Tinkling Cisticola Cisticola rufilatus, Black-chestedPrinia Prinia flavicans, Marico Flycatcher Bradornis mariquensis and Brown-crowned Tchagra Tchagra australis have not beenor are not widely recognised as mobile species.

The study of terrestrial bird communities has not been a verypopular subject in southern Africa during the last decades.The major studies on the subject, albeit many times onlyqualitatively, date back to the 1950–1980s when pioneers inthe field like JM Winterbottom, R Liversidge, CJ Vernon, WRTarboton, CJ Skead, GL Maclean and RK Brooke mappedbird communities for various biomes in southern Africa.Seasonal dynamics in southern African birds have beenstudied in forests by Koen (1992) and Symes et al. (2002)and in woodlands in Swaziland by Monadjem (2001, 2004).

R Liversidge and G Maclean provided ample informationon the birds of the Kalahari National Park (now KgalagadiTransfrontier Park), RSA, situated in the more arid part ofthe Kalahari basin. Both undertook studies over longer timeperiods of population changes (semi-quantitatively)(Maclean 1970b, Liversidge 1980, 1984) and occurrence ofbreeding (Maclean 1970a, 1970c) in relation to rainfall.Liversidge’s (1984) paper contained six years of data andrecords of over 63 000 birds, but few species were dis-cussed separately as most were combined and discussedas feeding assemblages (raptors, granivores and insecti-vores, each including long-distance migrants). For theremainder of the Kalahari basin (chiefly in Botswana), littlehas been published. At the other end of the Kalahari, nearLake Ngami in northern Botswana, Tree (1972) reported onspectacular changes in bird populations between a very wetyear and a subsequent drought. Qualitative changes in thepresence of some Kalahari species beyond the normalbreeding range in northern Botswana were reported byMaclean (1987). Seasonal changes in bird populations (withan emphasis on migrants) have been analysed by

Herremans (1993) for the Kalahari in Botswana, based ondata collected during a consecutive dry and wet season.

Rainfall is erratic in the Kalahari and although the yearlyaverage is 200–350mm, rains are very unreliable, and annu-al variation is large, from nearly nothing to over 500mm. Atleast 20mm should fall in a fortnight to have any effect on thevegetation (Liversidge 1984). When this does not happenduring the growing season in summer, the area becomesdrought-stricken until substantial rain falls at some later time.Drought is a recurrent phenomenon in the Kalahari biome. Infact, if it was not for the regular and profound effects of thedrought, such as the killing of large numbers of trees andshrubs, the Kalahari would be a rich and dense woodlandinstead of an open savanna shrubland and savanna wood-land. On the other hand, birds in the Kalahari basin mainlybreed during the wet season (Harrison et al. 1997), andabundant rains are a trigger for mass breeding in mostspecies, while drought suppresses breeding (Maclean1970a, 1970c, Lloyd 1999). This results in a paradox, where-by species that depend on the drought for maintaining thestructural quality of their preferred shrubland and opensavanna-woodland habitat suffer from severely reducedreproductive output and probably increased mortality duringsuch droughts. After a series of wet years with good breed-ing, populations of many songbirds peak, but for many thehabitat becomes critically encroached by coppicing bushesor tall grasses. During severe drought, the habitat structureimproves for many species, but feeding opportunities deteri-orate and breeding fails. Furthermore, the annual dry sea-son also has an impact on many species and substantialnumbers of birds migrate during the cold dry season to the

Introduction

Ostrich 2004, 75(4): 217–227Printed in South Africa — All rights reserved

Copyright © NISC Pty Ltd

OSTRICHISSN 0030–6525

Effects of drought on birds in the Kalahari, Botswana

Marc HerremansNatuurpunt Studie, Kardinaal Mercierplein 1, 2300 Mechelen, Belgium

e-mail: marc.herremans@natuurpunt.be

Results are presented from point-counts at six sites in the Kalahari in Botswana. Counts were repeated three times: during adry season following good rains (1991), during the next wet season when rains were far below average, and the following dryseason (1992) when the area became drought-stricken. Compared to the wet season, bird numbers decreased during thedrought by 37–81% and species by 8–52%; compared to the previous dry season, birds decreased by 5–71% and species by2–47%. Bird diversity (relative to numbers) tended to increase during the wet season but was little affected by drought, exceptin the northern Kalahari, where a greater proportion of birds moved out in response to drought. This gave the northern Kalaharithe most distinct bird community during a wet cycle, but it became again typically Kalahari during the drought. Thus, the typ-ical Kalahari bird communities expanded their range during drought into the moister periphery. Changes in numbers, mostprobably resulting from (local) movements were found in many species. Most confirmed earlier reports on their nomadic naturebut some, like Red-crested Lophotis ruficrista and Northern Black Afrotis afraoides Korhaan, Chestnut-vented Tit-BabblerParisoma subcaeruleum, Ant-eating Chat Myrmecocichla formicivora, Tinkling Cisticola Cisticola rufilatus, Black-chestedPrinia Prinia flavicans, Marico Flycatcher Bradornis mariquensis and Brown-crowned Tchagra Tchagra australis have not beenor are not widely recognised as mobile species.

The study of terrestrial bird communities has not been a verypopular subject in southern Africa during the last decades.The major studies on the subject, albeit many times onlyqualitatively, date back to the 1950–1980s when pioneers inthe field like JM Winterbottom, R Liversidge, CJ Vernon, WRTarboton, CJ Skead, GL Maclean and RK Brooke mappedbird communities for various biomes in southern Africa.Seasonal dynamics in southern African birds have beenstudied in forests by Koen (1992) and Symes et al. (2002)and in woodlands in Swaziland by Monadjem (2001, 2004).

R Liversidge and G Maclean provided ample informationon the birds of the Kalahari National Park (now KgalagadiTransfrontier Park), RSA, situated in the more arid part ofthe Kalahari basin. Both undertook studies over longer timeperiods of population changes (semi-quantitatively)(Maclean 1970b, Liversidge 1980, 1984) and occurrence ofbreeding (Maclean 1970a, 1970c) in relation to rainfall.Liversidge’s (1984) paper contained six years of data andrecords of over 63 000 birds, but few species were dis-cussed separately as most were combined and discussedas feeding assemblages (raptors, granivores and insecti-vores, each including long-distance migrants). For theremainder of the Kalahari basin (chiefly in Botswana), littlehas been published. At the other end of the Kalahari, nearLake Ngami in northern Botswana, Tree (1972) reported onspectacular changes in bird populations between a very wetyear and a subsequent drought. Qualitative changes in thepresence of some Kalahari species beyond the normalbreeding range in northern Botswana were reported byMaclean (1987). Seasonal changes in bird populations (withan emphasis on migrants) have been analysed by

Herremans (1993) for the Kalahari in Botswana, based ondata collected during a consecutive dry and wet season.

Rainfall is erratic in the Kalahari and although the yearlyaverage is 200–350mm, rains are very unreliable, and annu-al variation is large, from nearly nothing to over 500mm. Atleast 20mm should fall in a fortnight to have any effect on thevegetation (Liversidge 1984). When this does not happenduring the growing season in summer, the area becomesdrought-stricken until substantial rain falls at some later time.Drought is a recurrent phenomenon in the Kalahari biome. Infact, if it was not for the regular and profound effects of thedrought, such as the killing of large numbers of trees andshrubs, the Kalahari would be a rich and dense woodlandinstead of an open savanna shrubland and savanna wood-land. On the other hand, birds in the Kalahari basin mainlybreed during the wet season (Harrison et al. 1997), andabundant rains are a trigger for mass breeding in mostspecies, while drought suppresses breeding (Maclean1970a, 1970c, Lloyd 1999). This results in a paradox, where-by species that depend on the drought for maintaining thestructural quality of their preferred shrubland and opensavanna-woodland habitat suffer from severely reducedreproductive output and probably increased mortality duringsuch droughts. After a series of wet years with good breed-ing, populations of many songbirds peak, but for many thehabitat becomes critically encroached by coppicing bushesor tall grasses. During severe drought, the habitat structureimproves for many species, but feeding opportunities deteri-orate and breeding fails. Furthermore, the annual dry sea-son also has an impact on many species and substantialnumbers of birds migrate during the cold dry season to the

Introduction

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Herremans218

north and east of the Kalahari into more mesic vegetations(Harrison et al. 1997). These more or less regular move-ments and other more erratic movements are poorlymapped or understood in the Kalahari, and in many speciesthe proportion of the birds involved is probably variable,depending on local conditions.

The present paper investigates the effects of drought onbird communities in several parts of the Kalahari inBotswana. It compares the results from three bird counts ateach of six sites: once during the dry season of a wet year(1991), the second time during the next wet season (1992)when the rains failed, and a third time six months later dur-ing the subsequent dry season when the Kalahari becamedrought-stricken. Assessments are made of the effect of thedrought on bird and species numbers, the relative diversityof the bird communities and bird movements.

Material and methods

Point transect countsBird communities were sampled by point transect counts,chiefly from the canopy of a vehicle along 4x4-quality tracks.Six transects were counted in the Kalahari at the end of thedry season (mid-September to early November) in 1991,and these were repeated during the next wet season(February 1992) and the next dry season (late June to mid-July 1992). These counts are a subset of the data used toassess the place of long-distance migrants in seasonaldynamics in bird populations in the Kalahari (Herremans1993), but with an additional count in the dry season of1992, and with analyses now pertaining to residents (includ-ing nomads) instead of well-known migrants. The transectswere selected after a preliminary survey and aimed to berepresentative for the major vegetation types of the region(Table 1).

Each transect consisted of 20 points at least 250m apartin a vegetation type as uniform and representative for thearea as possible. All birds heard or seen within a cylinder of75m radius from the observer were recorded during 10 min-utes at each point, including birds flying past or overhead.Twelve points were counted in the first three hours after sun-rise and eight were covered in the last two hours before sun-set. Morning and evening counts were either on the sameday, or on consecutive days (evening and next morning).Repeated counts were made from exactly the same points.

The call of the Pear-spotted Owlet Glaucidium perlatumwas imitated during the second part of each count to promptthe appearance of more unobtrusive species. If applied for a

short period at moderate volume, this method resulted inmost birds in the immediate neighbourhood starting mob-bing, but an influx from beyond the count perimeter to jointhe mobbing was never observed. When females of territori-al (singing) males were not observed, they were neverthe-less assumed to be present and added to the count.However, this correction was only applied for unobtrusivesmall species (e.g. some larks) that normally occur in pairsin home ranges less than the area surveyed from each point.Unidentified birds were recorded, but were disregarded inthe analysis (on average only 0.01%).

Vegetation structureStructural diversity of the vegetation was recorded duringthe first counts (dry season of 1991, when the veld was ingood condition). The following classes were estimated: per-cent cover by grasses (0–25cm, 25cm–1m, >1m), percentcover by herbs (0–25cm, 25cm–1m), percent cover by bush-es and trees (0–1m, 1–3.5m, 3.5–7m, 7–14m, >14m) andpercent foliage. From these classes the Shannon index (H')of structural diversity was calculated (Table 1): H' = sum(pi.ln(pi)). The lower this index, the more open, low and uni-form the vegetation, while a higher index indicates a struc-turally diverse woodland with grasses, shrubs and trees ofdifferent sizes.

Illustrations approaching the above vegetation types canbe found in Harrison et al. (1997) for the Nata Delta (Figure51 Sowa Pan), Southern Kalahari savanna (Figure 44),Central Kalahari savanna-woodland (Figure 42) andNorthern Kalahari woodland-savanna (Figure 41), and forKalahari grassland in Penry (1994 — Central KalahariDeception Valley).

Diversity by rarefactionBird diversity can intuitively be described as the chance thatthe next bird is of a different species than the previous one.Comparing the diversity in samples of different overall size(whether or not resulting from differences in sampling effortor survey efficiency) remains difficult, but is possible with therarefaction diversity measurement. On the basis of the rela-tive frequencies of species recorded, this statistic allowsback-calculation of the probability that a species wasalready present in any smaller sample, and hence allows anestimate of the number of species in any smaller sample(Simberloff 1972, Heck et al. 1975, Magurran 1988). Theestimates of species richness can then be compared for twosamples at a point of common sample size (by necessityequal to or smaller than the smallest sample). Although rar-

Table 1: Localities and vegetation types for bird counts in the Kalahari (Botswana), ranked from open short grassland to more woody savan-nas (H' = Shannon index of structural diversity of the vegetation)

Locality Co-ordinates Vegetation type H'Nata Delta 20°22’S, 26°18’E delta grassland 0.74Sekoma(g) 24°25’S, 24°05’E Kalahari grassland 1.09Kgoro 25°25’S, 25°30’E Acacia tortilis bushveld 1.54Sekoma(s) 24°34’S, 24°03’E Southern Kalahari savanna 1.86Kutse 23°22’S, 24°26’E Central Kalahari savanna 1.90Phuduhudu 20°10’S, 24°37’E Northern Kalahari savanna 1.91

Herremans218

north and east of the Kalahari into more mesic vegetations(Harrison et al. 1997). These more or less regular move-ments and other more erratic movements are poorlymapped or understood in the Kalahari, and in many speciesthe proportion of the birds involved is probably variable,depending on local conditions.

The present paper investigates the effects of drought onbird communities in several parts of the Kalahari inBotswana. It compares the results from three bird counts ateach of six sites: once during the dry season of a wet year(1991), the second time during the next wet season (1992)when the rains failed, and a third time six months later dur-ing the subsequent dry season when the Kalahari becamedrought-stricken. Assessments are made of the effect of thedrought on bird and species numbers, the relative diversityof the bird communities and bird movements.

Material and methods

Point transect countsBird communities were sampled by point transect counts,chiefly from the canopy of a vehicle along 4x4-quality tracks.Six transects were counted in the Kalahari at the end of thedry season (mid-September to early November) in 1991,and these were repeated during the next wet season(February 1992) and the next dry season (late June to mid-July 1992). These counts are a subset of the data used toassess the place of long-distance migrants in seasonaldynamics in bird populations in the Kalahari (Herremans1993), but with an additional count in the dry season of1992, and with analyses now pertaining to residents (includ-ing nomads) instead of well-known migrants. The transectswere selected after a preliminary survey and aimed to berepresentative for the major vegetation types of the region(Table 1).

Each transect consisted of 20 points at least 250m apartin a vegetation type as uniform and representative for thearea as possible. All birds heard or seen within a cylinder of75m radius from the observer were recorded during 10 min-utes at each point, including birds flying past or overhead.Twelve points were counted in the first three hours after sun-rise and eight were covered in the last two hours before sun-set. Morning and evening counts were either on the sameday, or on consecutive days (evening and next morning).Repeated counts were made from exactly the same points.

The call of the Pear-spotted Owlet Glaucidium perlatumwas imitated during the second part of each count to promptthe appearance of more unobtrusive species. If applied for a

short period at moderate volume, this method resulted inmost birds in the immediate neighbourhood starting mob-bing, but an influx from beyond the count perimeter to jointhe mobbing was never observed. When females of territori-al (singing) males were not observed, they were neverthe-less assumed to be present and added to the count.However, this correction was only applied for unobtrusivesmall species (e.g. some larks) that normally occur in pairsin home ranges less than the area surveyed from each point.Unidentified birds were recorded, but were disregarded inthe analysis (on average only 0.01%).

Vegetation structureStructural diversity of the vegetation was recorded duringthe first counts (dry season of 1991, when the veld was ingood condition). The following classes were estimated: per-cent cover by grasses (0–25cm, 25cm–1m, >1m), percentcover by herbs (0–25cm, 25cm–1m), percent cover by bush-es and trees (0–1m, 1–3.5m, 3.5–7m, 7–14m, >14m) andpercent foliage. From these classes the Shannon index (H')of structural diversity was calculated (Table 1): H' = sum(pi.ln(pi)). The lower this index, the more open, low and uni-form the vegetation, while a higher index indicates a struc-turally diverse woodland with grasses, shrubs and trees ofdifferent sizes.

Illustrations approaching the above vegetation types canbe found in Harrison et al. (1997) for the Nata Delta (Figure51 Sowa Pan), Southern Kalahari savanna (Figure 44),Central Kalahari savanna-woodland (Figure 42) andNorthern Kalahari woodland-savanna (Figure 41), and forKalahari grassland in Penry (1994 — Central KalahariDeception Valley).

Diversity by rarefactionBird diversity can intuitively be described as the chance thatthe next bird is of a different species than the previous one.Comparing the diversity in samples of different overall size(whether or not resulting from differences in sampling effortor survey efficiency) remains difficult, but is possible with therarefaction diversity measurement. On the basis of the rela-tive frequencies of species recorded, this statistic allowsback-calculation of the probability that a species wasalready present in any smaller sample, and hence allows anestimate of the number of species in any smaller sample(Simberloff 1972, Heck et al. 1975, Magurran 1988). Theestimates of species richness can then be compared for twosamples at a point of common sample size (by necessityequal to or smaller than the smallest sample). Although rar-

Table 1: Localities and vegetation types for bird counts in the Kalahari (Botswana), ranked from open short grassland to more woody savan-nas (H' = Shannon index of structural diversity of the vegetation)

Locality Co-ordinates Vegetation type H'Nata Delta 20°22’S, 26°18’E delta grassland 0.74Sekoma(g) 24°25’S, 24°05’E Kalahari grassland 1.09Kgoro 25°25’S, 25°30’E Acacia tortilis bushveld 1.54Sekoma(s) 24°34’S, 24°03’E Southern Kalahari savanna 1.86Kutse 23°22’S, 24°26’E Central Kalahari savanna 1.90Phuduhudu 20°10’S, 24°37’E Northern Kalahari savanna 1.91

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Ostrich 2004, 75: 217–227 219

efaction calculates species richness for each sample size,the outcome is based on the relative abundance of speciesin the sample and therefore the rarefaction curve representsa true measure of diversity. Because the rarefaction statisticallows the calculation of confidence limits, the testing of dif-ferences is also possible.

Similarities Similarities in population composition between sites andseasons were calculated with Manhattan (city block) dis-tances (Cain and Harrison 1958, Gower 1985), and a treecluster with relative distance linking was used to visualisethe groupings. Calculations were performed with Statistica6.0 (Statsoft 2001).

Rainfall Rainfall was not measured at any of the study sites (neitherat any station close enough to be representative), and I canonly make vague general statements about the rains duringthe study. During the first months of 1991, the Inter-TropicalConvergence Zone (ITCZ) moved southwards over theKalahari several times and rains were widespread andabundant over the entire Kalahari basin. The average rain-fall at 12 stations across Botswana during the wet season of1990–1991 was 480mm, above average for the Kalahari inBotswana (250–500mm — Penry 1994). Kutse received par-ticularly good rains (c. 600mm). The veld conditionsremained excellent throughout the dry season of 1991,when the first counts were undertaken. The next summerrains (October 1991–April 1992) failed over most of theKalahari: the ITCZ only brought widespread rains to thenorthern parts of Botswana, barely touching the northernKalahari. Further south, the little rain that fell typically cameas isolated storms, resulting in important local variation inrainfall and typically making the effect of the subsequentdrought more severe in places than in others. This effectwas probably further enhanced by longer-term carry-overeffects of previous rainfall and ground moisture on vegeta-tion. Average rainfall at 12 stations throughout Botswana inthe wet season of 1991–1992 was 235mm, but these datainclude also stations in the more mesic north of the countrywhere rainfall in the range 500–600mm had been normal.Overall, the wet season 1991–1992 was the driest in theKalahari in Botswana between 1980–1994 (Herremans1994a). The count sites near Sekoma in the southernKalahari were the worst hit by the drought, which wasalready visible during the mid-summer count of early 1992.

Results

Species numbers and abundanceA total of 9 343 birds of 134 species were counted during the18 counts. Figure 1 presents an overview of the data struc-ture in terms of how commonly species were encountered.No species were found at all sites during each count. Themost widespread and abundant species were Scaly-feath-ered Finch Sporopipes squamifrons, Black-chested PriniaPrinia flavicans, Kalahari Scrub-robin Cercotrichas paenaand Fawn-coloured Lark Calendulauda africanoides (groupat upper right in Figure 1). Despite being widespread, the

Chat Flycatcher Bradornis infuscatus was remarkablysparse (Figure 1, lower right). At the opposite end of thespectrum, the Red-headed Finch Amadina erythrocephalawas localised, but unusually abundant (Figure 1, top left),most closely followed by Red-billed Quelea Quelea queleain this respect. Red-capped Lark Calandrella cinerea, Pink-billed Lark Spizocorys conirostris, Kittlitz’ Plover Charadriuspecuarius, Crested Francolin Dendroperdix sephaena,Shaft-tailed Whydah Vidua regia, Yellow-throatedSandgrouse Pterocles gutturalis, Magpie Shrike Corvinellamelanoleuca and Lesser Masked-weaver Ploceus inter-medius were found only at one or two sites, but were local-ly numerous. Just over one third of all species (44 species)were uncommonly recorded in only one to four of the counts(Figure 1, left bottom).

Bird numbers changed inconsistently from a rich dry to aconsecutive poor wet season (Figure 2a). There were twosites with little change (1–3% decrease), two with a cleardecline (14–28%) and two with an increase (48–92%). AtKutse numbers (already high) nearly doubled, but this wasentirely due to an influx of large flocks of Red-headed

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Figure 1: Abundance plots of the species recorded during repeat-ed transect counts in the Kalahari in Botswana: abundance (loga-rithm of the total number of birds counted) against the total numberof transects in which the species was encountered

Ostrich 2004, 75: 217–227 219

efaction calculates species richness for each sample size,the outcome is based on the relative abundance of speciesin the sample and therefore the rarefaction curve representsa true measure of diversity. Because the rarefaction statisticallows the calculation of confidence limits, the testing of dif-ferences is also possible.

Similarities Similarities in population composition between sites andseasons were calculated with Manhattan (city block) dis-tances (Cain and Harrison 1958, Gower 1985), and a treecluster with relative distance linking was used to visualisethe groupings. Calculations were performed with Statistica6.0 (Statsoft 2001).

Rainfall Rainfall was not measured at any of the study sites (neitherat any station close enough to be representative), and I canonly make vague general statements about the rains duringthe study. During the first months of 1991, the Inter-TropicalConvergence Zone (ITCZ) moved southwards over theKalahari several times and rains were widespread andabundant over the entire Kalahari basin. The average rain-fall at 12 stations across Botswana during the wet season of1990–1991 was 480mm, above average for the Kalahari inBotswana (250–500mm — Penry 1994). Kutse received par-ticularly good rains (c. 600mm). The veld conditionsremained excellent throughout the dry season of 1991,when the first counts were undertaken. The next summerrains (October 1991–April 1992) failed over most of theKalahari: the ITCZ only brought widespread rains to thenorthern parts of Botswana, barely touching the northernKalahari. Further south, the little rain that fell typically cameas isolated storms, resulting in important local variation inrainfall and typically making the effect of the subsequentdrought more severe in places than in others. This effectwas probably further enhanced by longer-term carry-overeffects of previous rainfall and ground moisture on vegeta-tion. Average rainfall at 12 stations throughout Botswana inthe wet season of 1991–1992 was 235mm, but these datainclude also stations in the more mesic north of the countrywhere rainfall in the range 500–600mm had been normal.Overall, the wet season 1991–1992 was the driest in theKalahari in Botswana between 1980–1994 (Herremans1994a). The count sites near Sekoma in the southernKalahari were the worst hit by the drought, which wasalready visible during the mid-summer count of early 1992.

Results

Species numbers and abundanceA total of 9 343 birds of 134 species were counted during the18 counts. Figure 1 presents an overview of the data struc-ture in terms of how commonly species were encountered.No species were found at all sites during each count. Themost widespread and abundant species were Scaly-feath-ered Finch Sporopipes squamifrons, Black-chested PriniaPrinia flavicans, Kalahari Scrub-robin Cercotrichas paenaand Fawn-coloured Lark Calendulauda africanoides (groupat upper right in Figure 1). Despite being widespread, the

Chat Flycatcher Bradornis infuscatus was remarkablysparse (Figure 1, lower right). At the opposite end of thespectrum, the Red-headed Finch Amadina erythrocephalawas localised, but unusually abundant (Figure 1, top left),most closely followed by Red-billed Quelea Quelea queleain this respect. Red-capped Lark Calandrella cinerea, Pink-billed Lark Spizocorys conirostris, Kittlitz’ Plover Charadriuspecuarius, Crested Francolin Dendroperdix sephaena,Shaft-tailed Whydah Vidua regia, Yellow-throatedSandgrouse Pterocles gutturalis, Magpie Shrike Corvinellamelanoleuca and Lesser Masked-weaver Ploceus inter-medius were found only at one or two sites, but were local-ly numerous. Just over one third of all species (44 species)were uncommonly recorded in only one to four of the counts(Figure 1, left bottom).

Bird numbers changed inconsistently from a rich dry to aconsecutive poor wet season (Figure 2a). There were twosites with little change (1–3% decrease), two with a cleardecline (14–28%) and two with an increase (48–92%). AtKutse numbers (already high) nearly doubled, but this wasentirely due to an influx of large flocks of Red-headed

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Figure 1: Abundance plots of the species recorded during repeat-ed transect counts in the Kalahari in Botswana: abundance (loga-rithm of the total number of birds counted) against the total numberof transects in which the species was encountered

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Finches, with a total of 628 being recorded (from sevencount points) in the summer of 1992, only 18 at four pointsthe previous dry season and none at all during the next dryseason (drought). From the wet season of 1992 to the nextdry season (drought), numbers declined consistently at all

six sites; declines ranged between 37–81%. Compared tothe previous dry season, birds decreased by 5–71%.

The number of species generally increased from the dryseason of 1991 to the next wet season (6–43%, Figure 2b).Only at one site (southern Kalahari savanna at Sekoma) didthe number of species decrease (14%), paralleled by thelargest decrease in the number of birds from dry to wet sea-son (28%). After the rains failed in the wet season of 1992,species numbers dropped consistently (8–52%) whendrought was apparent in the next dry season. Compared tothe previous dry season, species decreased by 2–47%.

DiversityThe following figures each present rarefaction curves for thethree seasonal counts at each of the sites, allowing compar-ison of changes in bird diversity from a rich dry season to apoor wet season and the subsequent drought. At the NataDelta, bird diversity increased (not significantly) during thewet season, but declined significantly during the drought(Figure 3a). In the southern Kalahari grasslands (at Sekoma(g)), diversity increased significantly during the wet season,but despite the spectacular reduction in bird numbers andspecies during the drought, relative diversity remained simi-lar (Figure 3b). At Kgoro, bird diversity increased significant-ly during the wet season, but remained stable during thedrought (Figure 3c). In the southern Kalahari woodland-savanna (at Sekoma (s)), diversity had already decreasedduring the wet season of 1992, but did not change much fur-ther during the drought (Figure 3d). In the central Kalahariwoodland savanna (at Kutse) there were no changes in birddiversity during the study when the superabundance of Red-headed Finches is excluded; evidently, when the finches areincluded, relative diversity is somewhat depressed (Figure3e). In the northern Kalahari woodland savanna (atPhuduhudu), diversity significantly increased during the wetseason and decreased significantly during the drought(Figure 3f). Overall, there is a tendency for increased diver-sity during the wet season, but relatively little change duringdrought, except in the periphery of the Kalahari (Nata,Phuduhudu, Kgoro), where birds have only a relatively smalldistance to cross to reliably find richer vegetation.

With these data and procedures at hand, it is also possi-ble to compare the diversity between all the sites in the dryseason, the wet season and the drought respectively, eachtime at a common sample size, and plot this relative diversi-ty against the vegetation diversity (Figure 4a–c). While thereis a close correlation between the bird diversity and thestructural diversity of the vegetation when the veld was ingood condition during the dry season of 1991, following agood year of rains (Figure 4a), this relation starts to fade dur-ing the summer of 1992 when the rains failed and during thesubsequent drought (Figures 4b–c).

SimilaritiesThe richer savanna woodlands of the central and northernKalahari (Kutse and Phuduhudu) have the most distinct birdpopulations (Figure 5). At the other end, the grasslands(Nata and Sekoma (g)) have the most similar bird popula-tions (i.e. have the lowest linking distances). At most sites,bird populations are more similar to each other and more

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Figure 2: Changes in bird populations during drought, as recordedduring repeated transect counts in the Kalahari in Botswana: (a)total bird numbers, (b) number of species

Herremans220

Finches, with a total of 628 being recorded (from sevencount points) in the summer of 1992, only 18 at four pointsthe previous dry season and none at all during the next dryseason (drought). From the wet season of 1992 to the nextdry season (drought), numbers declined consistently at all

six sites; declines ranged between 37–81%. Compared tothe previous dry season, birds decreased by 5–71%.

The number of species generally increased from the dryseason of 1991 to the next wet season (6–43%, Figure 2b).Only at one site (southern Kalahari savanna at Sekoma) didthe number of species decrease (14%), paralleled by thelargest decrease in the number of birds from dry to wet sea-son (28%). After the rains failed in the wet season of 1992,species numbers dropped consistently (8–52%) whendrought was apparent in the next dry season. Compared tothe previous dry season, species decreased by 2–47%.

DiversityThe following figures each present rarefaction curves for thethree seasonal counts at each of the sites, allowing compar-ison of changes in bird diversity from a rich dry season to apoor wet season and the subsequent drought. At the NataDelta, bird diversity increased (not significantly) during thewet season, but declined significantly during the drought(Figure 3a). In the southern Kalahari grasslands (at Sekoma(g)), diversity increased significantly during the wet season,but despite the spectacular reduction in bird numbers andspecies during the drought, relative diversity remained simi-lar (Figure 3b). At Kgoro, bird diversity increased significant-ly during the wet season, but remained stable during thedrought (Figure 3c). In the southern Kalahari woodland-savanna (at Sekoma (s)), diversity had already decreasedduring the wet season of 1992, but did not change much fur-ther during the drought (Figure 3d). In the central Kalahariwoodland savanna (at Kutse) there were no changes in birddiversity during the study when the superabundance of Red-headed Finches is excluded; evidently, when the finches areincluded, relative diversity is somewhat depressed (Figure3e). In the northern Kalahari woodland savanna (atPhuduhudu), diversity significantly increased during the wetseason and decreased significantly during the drought(Figure 3f). Overall, there is a tendency for increased diver-sity during the wet season, but relatively little change duringdrought, except in the periphery of the Kalahari (Nata,Phuduhudu, Kgoro), where birds have only a relatively smalldistance to cross to reliably find richer vegetation.

With these data and procedures at hand, it is also possi-ble to compare the diversity between all the sites in the dryseason, the wet season and the drought respectively, eachtime at a common sample size, and plot this relative diversi-ty against the vegetation diversity (Figure 4a–c). While thereis a close correlation between the bird diversity and thestructural diversity of the vegetation when the veld was ingood condition during the dry season of 1991, following agood year of rains (Figure 4a), this relation starts to fade dur-ing the summer of 1992 when the rains failed and during thesubsequent drought (Figures 4b–c).

SimilaritiesThe richer savanna woodlands of the central and northernKalahari (Kutse and Phuduhudu) have the most distinct birdpopulations (Figure 5). At the other end, the grasslands(Nata and Sekoma (g)) have the most similar bird popula-tions (i.e. have the lowest linking distances). At most sites,bird populations are more similar to each other and more

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Figure 2: Changes in bird populations during drought, as recordedduring repeated transect counts in the Kalahari in Botswana: (a)total bird numbers, (b) number of species

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Figure 3: Changes in bird diversity according to season and drought. Results from the rarefaction diversity measure: each bold curve repre-sents the expected species number at increasing sample sizes in a particular season. Thin lines are 99% confidence limits (only drawn forthe season taking up the centre position): when the confidence limits of one season overlap with the bold curve of another season at a par-ticular sample size, the differences are not significant (at 1%). a) Nata (delta grasslands); b) Sekoma (southern Kalahari grassland); c) Kgoro(Acacia tortilis bushveld); d) Sekoma (southern Kalahari woodland-savanna); e) Kutse (central Kalahari woodland-savanna); f) Phuduhudu(northern Kalahari savanna-woodland)

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Figure 4: Relationship between the structural diversity of the vegetation (H') and the expected bird species richness (at the maximal com-mon sample size E(x) from rarefaction) at the six sites, during (a) the dry season of 1991 (x = 150), (b) the failing wet season of 1992 (x =220) and (c) the subsequent drought in 1992 (x = 40)

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Figure 3: Changes in bird diversity according to season and drought. Results from the rarefaction diversity measure: each bold curve repre-sents the expected species number at increasing sample sizes in a particular season. Thin lines are 99% confidence limits (only drawn forthe season taking up the centre position): when the confidence limits of one season overlap with the bold curve of another season at a par-ticular sample size, the differences are not significant (at 1%). a) Nata (delta grasslands); b) Sekoma (southern Kalahari grassland); c) Kgoro(Acacia tortilis bushveld); d) Sekoma (southern Kalahari woodland-savanna); e) Kutse (central Kalahari woodland-savanna); f) Phuduhudu(northern Kalahari savanna-woodland)

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Figure 4: Relationship between the structural diversity of the vegetation (H') and the expected bird species richness (at the maximal com-mon sample size E(x) from rarefaction) at the six sites, during (a) the dry season of 1991 (x = 150), (b) the failing wet season of 1992 (x =220) and (c) the subsequent drought in 1992 (x = 40)

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distinct from the other sites regardless of season, except forPhuduhudu. This indicates that despite the general unifor-mity of bird communities in the Kalahari, there is still quite asubstantial local specialisation. During the wet season, thebird populations at Phuduhudu in the richer woodlands in thenorthern Kalahari are the most distinct of all, but the birdpopulations remaining during the drought are very similar tothose of the rest of the Kalahari (Phuduhudu 92D shifts intothe Kalahari cluster).

Species-specific patternsOverall, only 81 species were encountered sufficiently fre-quently and commonly to judge changes between seasons(flocking species recorded in relatively low numbers werealso excluded here). Of these, 48 (=58%) showed changesthat are considered sufficiently large to reflect a patternrather than occasional fluctuations. The majority of speciesshowed a consistent decline during the 1992 dry season(drought) (Table 2). In another 11 species, numbers alsodeclined considerably during the drought, but lower numbersoccurred during both dry seasons, and changes thereforerather indicate a pattern of wet season visitors to theKalahari (Table 3). Three species increased during thedrought (Table 4), of which the Fiscal Flycatcher andCommon Fiscal are known dry season visitors to theKalahari basin in varying numbers (see references in Table4).

A number of species showed inconsistent changes, themost striking of which are presented in Table 5. Fawn-coloured Larks increased during the dry seasons at twosites, most notably at the eastern edge of the Kalahari in

Kgoro, where during the drought of 1992 two birds wereobserved belonging to the pale-plumaged race sarwensis,which breed further west on Kalahari sands. The numbersdecreased during the drought at three other sites, includingat both ends, the drier southern Kalahari (Sekoma) and themoister northern Kalahari (Phuduhudu). African Red-eyedBulbul Pycnonotus nigricans data illustrate the commonknowledge that it is a wet season visitor to the drier parts ofthe Kalahari and that there are dry season influxes into thenorthern and eastern periphery of the Kalahari, also beyondthe breeding range. Chestnut-vented Tit-Babblers Parisomasubcaeruleum show a pattern of a dry season influx at theeastern edge of the Kalahari (Kgoro), a decline in theKalahari during the drought (both ends — Sekoma andPhuduhudu) and an increase at Kutse (where rains hadbeen particularly good in 1991). Marico FlycatchersBradornis mariquensis showed important changes that,however, may still mainly be chance-related in a flockingspecies, except for Phuduhudu where there is a more promi-nent decline during the drought. Scaly-feathered Finchesand Violet-eared Waxbills Granatina granatina declinedthroughout most of the Kalahari during the drought, butincreased at the northern periphery.

Discussion

MethodsPrevious authors (Maclean 1970b, Liversidge 1984) collect-ed huge datasets over many months in the KgalagadiTransfrontier Park, but were somewhat concerned that theydid not use a strict standard procedure for the counts. The

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Herremans222

distinct from the other sites regardless of season, except forPhuduhudu. This indicates that despite the general unifor-mity of bird communities in the Kalahari, there is still quite asubstantial local specialisation. During the wet season, thebird populations at Phuduhudu in the richer woodlands in thenorthern Kalahari are the most distinct of all, but the birdpopulations remaining during the drought are very similar tothose of the rest of the Kalahari (Phuduhudu 92D shifts intothe Kalahari cluster).

Species-specific patternsOverall, only 81 species were encountered sufficiently fre-quently and commonly to judge changes between seasons(flocking species recorded in relatively low numbers werealso excluded here). Of these, 48 (=58%) showed changesthat are considered sufficiently large to reflect a patternrather than occasional fluctuations. The majority of speciesshowed a consistent decline during the 1992 dry season(drought) (Table 2). In another 11 species, numbers alsodeclined considerably during the drought, but lower numbersoccurred during both dry seasons, and changes thereforerather indicate a pattern of wet season visitors to theKalahari (Table 3). Three species increased during thedrought (Table 4), of which the Fiscal Flycatcher andCommon Fiscal are known dry season visitors to theKalahari basin in varying numbers (see references in Table4).

A number of species showed inconsistent changes, themost striking of which are presented in Table 5. Fawn-coloured Larks increased during the dry seasons at twosites, most notably at the eastern edge of the Kalahari in

Kgoro, where during the drought of 1992 two birds wereobserved belonging to the pale-plumaged race sarwensis,which breed further west on Kalahari sands. The numbersdecreased during the drought at three other sites, includingat both ends, the drier southern Kalahari (Sekoma) and themoister northern Kalahari (Phuduhudu). African Red-eyedBulbul Pycnonotus nigricans data illustrate the commonknowledge that it is a wet season visitor to the drier parts ofthe Kalahari and that there are dry season influxes into thenorthern and eastern periphery of the Kalahari, also beyondthe breeding range. Chestnut-vented Tit-Babblers Parisomasubcaeruleum show a pattern of a dry season influx at theeastern edge of the Kalahari (Kgoro), a decline in theKalahari during the drought (both ends — Sekoma andPhuduhudu) and an increase at Kutse (where rains hadbeen particularly good in 1991). Marico FlycatchersBradornis mariquensis showed important changes that,however, may still mainly be chance-related in a flockingspecies, except for Phuduhudu where there is a more promi-nent decline during the drought. Scaly-feathered Finchesand Violet-eared Waxbills Granatina granatina declinedthroughout most of the Kalahari during the drought, butincreased at the northern periphery.

Discussion

MethodsPrevious authors (Maclean 1970b, Liversidge 1984) collect-ed huge datasets over many months in the KgalagadiTransfrontier Park, but were somewhat concerned that theydid not use a strict standard procedure for the counts. The

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Figure 5: Similarities in bird populations between sites and seasons; tree diagram with linking based upon Manhattan distances

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Table 2: Species of which fewer were recorded either from when the rains failed (1992 wet) or during the drought (1992 dry)

91 dry 92 wet 92 dry ReferencesCrested Francolin Dendroperdix sephaena 10 7 0Red-crested Korhaan Lophotis ruficrista 61 29 8 ANorthern Black Korhaan Afrotis afraoides 54 51 18 SCape Turtle-dove Streptopelia capicola 130 122 13 E, G, R ,SEmerald-spotted Wood-dove Turtur chalcospilos 8 8 0 E, SSwallow-tailed Bee-eater Merops hirundineus 13 13 0 E, G, L, R, SAcacia Pied Barbet Tricholaema leucomelas 25 23 9 P, SRufous-naped Lark Mirafra africana 29 20 4 ESabota Lark Calendulauda sabota 55 22 18 SAshy Tit Parus cinerascens 22 14 9 SAnt-eating Chat Myrmecocichla formicivora 22 31 9Kalahari Scrub-robin Cercothrichas paena 221 157 147 B, MYellow-bellied Eremomela Eremomela icteropygialis 53 25 19 G, S, TDesert Cisticola Cisticola aridulus 90 68 0 E, I, K, R, STinkling Cisticola Cisticola rufilatus 41 41 2Rattling Cisticola Cisticola chiniana 34 15 3 G, RBlack-chested Prinia Prinia flavicans 354 298 115Crimson-breasted Shrike Laniarius atrococcineus 23 18 6 D, SBrown-crowned Tchagra Tchagra australis 68 34 4Wattled Starling Creatophora cinerea 26 45 0 E, G, L, N, P, Q, SCape Glossy Starling Lamprotornis nitens 45 50 12 O, SMarico Sunbird Cinnyris mariquensis 45 65 2 C, H, L, R, SWhite-bellied Sunbird Cinnyris talatala 19 40 1 C, H, R, SRed-billed Buffalo-weaver Bubalornis niger 9 4 0 A, G, SSouthern Masked-weaver Ploceus velatus 82 81 0 A, E, G, J, L, S, ULesser Masked-weaver Ploceus intermedius 12 0 0Red-billed Quelea Quelea quelea 272 18 0 A, E, F, G, L, SAfrican Quailfinch Ortygospiza atricollis 61 25 0 E, F, G, R, SGolden-breasted Bunting Emberiza flaviventris 34 20 0 E, S

References are published sources that indicate movements or drought-related changes in numbers for the species (A = Tree 1972, B =Hawker 2003, C = Herremans 1992, D = Ashby 1992, E = Brewster 1992, F = Wilson 1984, G = Brewster 1991, H = Borello 1992, I = Brewster1993, J = Dawson 1975, K = Brewster 1996, L = Pausch 1998, M = Muller 2002, N = Liversidge 1980, O = Liversidge 1984, P = Maclean1970a, Q = Maclean 1970b, R = Brooke 1994, S = Harrison et al. 1997, T = Maclean 1993, U = Herremans 1994b)

Table 3: Wet season visitors

91 dry 92 wet 92 dry ReferencesKittlitz’ Plover Charadrius pecuarius 0 26 0 B, F, MTemminck’s Courser Cursorius temminckii 0 12 2 C, F, H, MLaughing Dove Streptopelia senegalensis 3 79 1 A, C, F, L, MNamaqua Dove Oena capensis 3 74 0 A, C, F, I, J, K, L, MRed-capped Lark Calandrella cinerea 0 37 0 B, D, E, H, L, M, NPink-billed Lark Spizocorys conirostris 0 16 0 J, K, L, M, NCape Penduline Tit Anthoscopus minutus 0 25 1 G, MCapped Wheatear Oenanthe pileata 3 18 2 B, C, D, E, F, J, K, MBarred Wren-warbler Calamonastes fasciolatus 4 14 1 MPlain-backed Pipit (*) Anthus leucophrys 0 51 0 C, E, F, L, MRed-headed Finch Amadina erythrocephala 27 628 0 A, B, G, F, H, J, K, L, M

References are published sources that indicate movements or drought-related changes in numbers for the species (A = Brewster 1992, B =Wilson 1984, C = Brewster 1991, D = Brewster 1993, E = Brewster 1996, F = Pausch 1998, G = Muller 2002, H = Tree 1972, I = Maclean1987, J = Maclean 1970a, K = Maclean 1970b, L = Brooke 1994, M = Harrison et al. 1997, N = Maclean 1970c)(*) The counts were conducted before Richard Liversidge described two new migratory pipit species from Kimberley: Long-tailed Pipit Anthuslongicaudatus (Liversidge 1996) and Kimberley Pipit Anthus pseudosimilis (Liversidge 2002). It is unknown if (or how) the present data mayrelate to these new species subsequently described

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Table 2: Species of which fewer were recorded either from when the rains failed (1992 wet) or during the drought (1992 dry)

91 dry 92 wet 92 dry ReferencesCrested Francolin Dendroperdix sephaena 10 7 0Red-crested Korhaan Lophotis ruficrista 61 29 8 ANorthern Black Korhaan Afrotis afraoides 54 51 18 SCape Turtle-dove Streptopelia capicola 130 122 13 E, G, R ,SEmerald-spotted Wood-dove Turtur chalcospilos 8 8 0 E, SSwallow-tailed Bee-eater Merops hirundineus 13 13 0 E, G, L, R, SAcacia Pied Barbet Tricholaema leucomelas 25 23 9 P, SRufous-naped Lark Mirafra africana 29 20 4 ESabota Lark Calendulauda sabota 55 22 18 SAshy Tit Parus cinerascens 22 14 9 SAnt-eating Chat Myrmecocichla formicivora 22 31 9Kalahari Scrub-robin Cercothrichas paena 221 157 147 B, MYellow-bellied Eremomela Eremomela icteropygialis 53 25 19 G, S, TDesert Cisticola Cisticola aridulus 90 68 0 E, I, K, R, STinkling Cisticola Cisticola rufilatus 41 41 2Rattling Cisticola Cisticola chiniana 34 15 3 G, RBlack-chested Prinia Prinia flavicans 354 298 115Crimson-breasted Shrike Laniarius atrococcineus 23 18 6 D, SBrown-crowned Tchagra Tchagra australis 68 34 4Wattled Starling Creatophora cinerea 26 45 0 E, G, L, N, P, Q, SCape Glossy Starling Lamprotornis nitens 45 50 12 O, SMarico Sunbird Cinnyris mariquensis 45 65 2 C, H, L, R, SWhite-bellied Sunbird Cinnyris talatala 19 40 1 C, H, R, SRed-billed Buffalo-weaver Bubalornis niger 9 4 0 A, G, SSouthern Masked-weaver Ploceus velatus 82 81 0 A, E, G, J, L, S, ULesser Masked-weaver Ploceus intermedius 12 0 0Red-billed Quelea Quelea quelea 272 18 0 A, E, F, G, L, SAfrican Quailfinch Ortygospiza atricollis 61 25 0 E, F, G, R, SGolden-breasted Bunting Emberiza flaviventris 34 20 0 E, S

References are published sources that indicate movements or drought-related changes in numbers for the species (A = Tree 1972, B =Hawker 2003, C = Herremans 1992, D = Ashby 1992, E = Brewster 1992, F = Wilson 1984, G = Brewster 1991, H = Borello 1992, I = Brewster1993, J = Dawson 1975, K = Brewster 1996, L = Pausch 1998, M = Muller 2002, N = Liversidge 1980, O = Liversidge 1984, P = Maclean1970a, Q = Maclean 1970b, R = Brooke 1994, S = Harrison et al. 1997, T = Maclean 1993, U = Herremans 1994b)

Table 3: Wet season visitors

91 dry 92 wet 92 dry ReferencesKittlitz’ Plover Charadrius pecuarius 0 26 0 B, F, MTemminck’s Courser Cursorius temminckii 0 12 2 C, F, H, MLaughing Dove Streptopelia senegalensis 3 79 1 A, C, F, L, MNamaqua Dove Oena capensis 3 74 0 A, C, F, I, J, K, L, MRed-capped Lark Calandrella cinerea 0 37 0 B, D, E, H, L, M, NPink-billed Lark Spizocorys conirostris 0 16 0 J, K, L, M, NCape Penduline Tit Anthoscopus minutus 0 25 1 G, MCapped Wheatear Oenanthe pileata 3 18 2 B, C, D, E, F, J, K, MBarred Wren-warbler Calamonastes fasciolatus 4 14 1 MPlain-backed Pipit (*) Anthus leucophrys 0 51 0 C, E, F, L, MRed-headed Finch Amadina erythrocephala 27 628 0 A, B, G, F, H, J, K, L, M

References are published sources that indicate movements or drought-related changes in numbers for the species (A = Brewster 1992, B =Wilson 1984, C = Brewster 1991, D = Brewster 1993, E = Brewster 1996, F = Pausch 1998, G = Muller 2002, H = Tree 1972, I = Maclean1987, J = Maclean 1970a, K = Maclean 1970b, L = Brooke 1994, M = Harrison et al. 1997, N = Maclean 1970c)(*) The counts were conducted before Richard Liversidge described two new migratory pipit species from Kimberley: Long-tailed Pipit Anthuslongicaudatus (Liversidge 1996) and Kimberley Pipit Anthus pseudosimilis (Liversidge 2002). It is unknown if (or how) the present data mayrelate to these new species subsequently described

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present programme used a strict procedure, but used loweffort counts covering a single day at each site during threeconsecutive seasons; the question remains whether anythingnew can be detected in this way. The remark by Liversidge

(1980), that the Kalahari system is so variable that variationsshould be studied during many years and no conclusions bedrawn from a one-year study, is most relevant here. His owndata and those of Maclean (1970a, 1970b, 1970c) support

Table 4: Drought (1992 dry) visitors to the Kalahari basin

91 dry 92 wet 92 dry ReferencesRed-faced Mousebird Urocolius indicus 1 2 54 A, G, IFiscal Flycatcher Sigelus silens 0 0 8 B, C, D, E, F, ICommon Fiscal Lanius collaris 4 2 13 B, D, H, J

References are published sources that indicate movements or drought-related changes in numbers for the species (A = Herremans andHerremans-Tonnoeyr 1994, B = Brewster 1992, C = Wilson 1984, D = Anonymous 1989, E = Brewster 1993, F = Pausch 1998, G = Tyler2001, H = Brooke 1994, I = Harrison et al. 1997, J = Herremans 1994a)

91 dry 92 wet 92 dry ReferencesCrowned Lapwing Vanellus coronatus E, H, J, L, M

Kutse 0 8 22Nata 8 12 4Kgoro 0 10 0

Fawn-coloured Lark Calendulauda africanoides A, D, L, NKutse 51 27 56Kgoro 10 2 12Sekoma (s) 32 10 17Sekoma (g) 16 15 3Phuduhudu 44 47 15

Grey-backed Sparrowlark Eremopterix verticalis A, C, D, E, F, H, K, L, M, OKutse 0 93 5Nata 74 2 100

African Red-eyed Bulbul Pycnonotus nigricans A, C, D, G, I, K, MSekoma (s) 20 38 1Phuduhudu 26 19 38

Chestnut-vented Tit-babbler Parisoma subcaeruleum B, GKutse 4 1 40Kgoro 19 8 19Sekoma (s) 33 18 7Phuduhudu 38 31 19

Marico Flycatcher Bradornis mariquensis LKutse 12 6 13Kgoro 24 40 17Phuduhudu 35 41 11

African Pipit Anthus cinnamomeus D, E, H, L, MKutse 0 18 0Nata 28 9 12Kgoro 4 2 20

Scaly-feathered Finch Sporopipes squamifrons H, K, L, MKutse 220 430 331Kgoro 63 73 31Sekoma (s) 70 47 29Sekoma (g) 11 15 2Phuduhudu 12 20 136

Violet-eared Waxbill Granatina granatina H, MKutse 59 70 16Sekoma (s) 27 14 3Phuduhudu 27 36 44

References are published sources that indicate movements or drought-related changes in numbers for the species (A = Brewster 1992, B =Wilson 1984, C = Brewster 1991, D = Brewster 1993, E = Brewster 1996, F = Pausch 1998, G = Muller 2002, H = Tree 1972, I = Maclean1987, J = Liversidge 1984, K = Maclean 1970b, L = Brooke 1994, M = Harrison et al. 1997, N = Bishop et al. 1992, O = Maclean 1970c)

Table 5: Species with inconsistent, complex changes

Herremans224

present programme used a strict procedure, but used loweffort counts covering a single day at each site during threeconsecutive seasons; the question remains whether anythingnew can be detected in this way. The remark by Liversidge

(1980), that the Kalahari system is so variable that variationsshould be studied during many years and no conclusions bedrawn from a one-year study, is most relevant here. His owndata and those of Maclean (1970a, 1970b, 1970c) support

Table 4: Drought (1992 dry) visitors to the Kalahari basin

91 dry 92 wet 92 dry ReferencesRed-faced Mousebird Urocolius indicus 1 2 54 A, G, IFiscal Flycatcher Sigelus silens 0 0 8 B, C, D, E, F, ICommon Fiscal Lanius collaris 4 2 13 B, D, H, J

References are published sources that indicate movements or drought-related changes in numbers for the species (A = Herremans andHerremans-Tonnoeyr 1994, B = Brewster 1992, C = Wilson 1984, D = Anonymous 1989, E = Brewster 1993, F = Pausch 1998, G = Tyler2001, H = Brooke 1994, I = Harrison et al. 1997, J = Herremans 1994a)

91 dry 92 wet 92 dry ReferencesCrowned Lapwing Vanellus coronatus E, H, J, L, M

Kutse 0 8 22Nata 8 12 4Kgoro 0 10 0

Fawn-coloured Lark Calendulauda africanoides A, D, L, NKutse 51 27 56Kgoro 10 2 12Sekoma (s) 32 10 17Sekoma (g) 16 15 3Phuduhudu 44 47 15

Grey-backed Sparrowlark Eremopterix verticalis A, C, D, E, F, H, K, L, M, OKutse 0 93 5Nata 74 2 100

African Red-eyed Bulbul Pycnonotus nigricans A, C, D, G, I, K, MSekoma (s) 20 38 1Phuduhudu 26 19 38

Chestnut-vented Tit-babbler Parisoma subcaeruleum B, GKutse 4 1 40Kgoro 19 8 19Sekoma (s) 33 18 7Phuduhudu 38 31 19

Marico Flycatcher Bradornis mariquensis LKutse 12 6 13Kgoro 24 40 17Phuduhudu 35 41 11

African Pipit Anthus cinnamomeus D, E, H, L, MKutse 0 18 0Nata 28 9 12Kgoro 4 2 20

Scaly-feathered Finch Sporopipes squamifrons H, K, L, MKutse 220 430 331Kgoro 63 73 31Sekoma (s) 70 47 29Sekoma (g) 11 15 2Phuduhudu 12 20 136

Violet-eared Waxbill Granatina granatina H, MKutse 59 70 16Sekoma (s) 27 14 3Phuduhudu 27 36 44

References are published sources that indicate movements or drought-related changes in numbers for the species (A = Brewster 1992, B =Wilson 1984, C = Brewster 1991, D = Brewster 1993, E = Brewster 1996, F = Pausch 1998, G = Muller 2002, H = Tree 1972, I = Maclean1987, J = Liversidge 1984, K = Maclean 1970b, L = Brooke 1994, M = Harrison et al. 1997, N = Bishop et al. 1992, O = Maclean 1970c)

Table 5: Species with inconsistent, complex changes

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this, but unfortunately nowadays long-term studies are limit-ed by finance or other factors.

My approach had the advantage that several sites atgreat distances could be compared in a short period of time,but the low intensity sampling resulted in low numbers formany species (some 40% of all), precluding any furtherassessment for these at species level. Furthermore, countsin different seasons inevitably have to cope with changes inbird behaviour (territoriality, singing, flocking etc.) and vege-tation-dependent differences in visibility, meaning that evencounts with a strict procedure result at best in semi-quanti-tative data. To convert these to densities has some furtherrisks but, as an indication, it is estimated that in this studyapproximately 35ha were more or less effectively surveyedper transect count. The chance of detecting a bird from astationary point decreases with distance from the observer,and current wisdom and practice for standardisation of tran-sect counts is to calculate densities based on a species-spe-cific detection probability function (see, for example, pro-gramme ‘distance’ at http://www.ruwpa.st-and.ac.uk/dis-tance/). No matter how correct this approach may be in the-ory, in practice variances on density estimates may becomeso large that it is difficult to maintain statistically that anybirds were indeed present at all (see, for example, alsoDean and Milton 2001).

ChangesLiversidge (1966) recorded a drop in the bird breeding pop-ulation of 31% in numbers and 28% in species between adrought and wet year in a moderately drought-sensitive areain the Eastern Cape. The Kalahari data show much largerchanges, 37–81% in numbers, and are more similar to thoseobtained between a wet and dry cycle in the more aridsouthern Karoo: 70% of bird numbers and 63% of species(Dean and Milton 2001). Maclean (1970b) considered morethan half the bird species in the Kalahari to be nomadic. Inthis study, some 60% of the species with sufficiently largesamples showed considerable changes from dry to wet sea-son or from wet season to drought. Such changes may,however, have several causes: (1) mere chance effects dur-ing sampling — the present programme with counts on asingle day covering only c. 35ha may be particularly sensi-tive to such effects. Low density species, particularly whenlikely to flock at some stage during the year are especially atrisk; (2) changes in conspicuousness and visibility; (3) a realdecline or increase in numbers, which can be the result ofmortality or breeding; (4) emigration or immigration. The firsttwo points reflect sampling variation and error while the lat-ter two are more interesting for population dynamics, butunfortunately with the present method mortality and emigra-tion cannot be distinguished. Breeding was limited duringthe dry summer of 1992, so reproductive output will hardlyhave had a major impact on numbers. Chance effects haveprobably mostly been avoided by selecting only the 60% ofspecies with larger samples. Changes in conspicuousnessmay to some extent affect the data for many species, but inthe final selection (Tables 2–5) it appears that only forCrested Francolin and Barred Wren-warbler Calamonastesfasciolatus might this be the principal factor for the recordedchanges. Both species are very unobtrusive when not call-

ing, and the numbers in the samples are fairly low.Furthermore, for neither of the species did I find literaturereferences indicating the possibility of movements. Similarconsideration could be made for Tinkling Cisticola Cisticolarufilatu, Rufous-naped Lark Mirafra africana and Brown-crowned Tchagra Tchagra australis, except that here goodnumbers were recorded during the 1991 dry season as well,making the decline probably real. Furthermore, the cisticolaresponds well to Pearl-spotted Owlet calls and is thus rela-tively easy to record; it also fits the pattern of congenericspecies, which all lose the grassy component of their habitatduring drought in the Kalahari. I consider it unlikely thatthese species suffered such a high mortality rate so sooninto a drought period; the drought continued well into 1994,and if mortality would already have such an impact duringthe first months of a drought, there would not be many leftduring prolonged droughts. I suggest that these speciesshould be watched more closely in future for (local) move-ments. The Ant-eating Chat Myrmecocichla formicivora isanother species for which I did not find literature evidencefor movements, but because it is conspicuous and respondswell to Pearl-spotted Owlet calls, the counts are reliable, andmovements are a likely explanation. The korhaans also forman intriguing case. Red-crested Korhaan Lophotis ruficristacan be very unobtrusive in dense shrubland when not call-ing, and I accept that I failed to record them during thedrought when not calling. However, Tree (1972), duringmonths of observation from a bush camp, also noted thatthis species became much less common in the northernKalahari in a severe drought. It is likely that some move intonearby moister woodlands during dry cycles. Northern BlackKorhaans Afrotis afraoides were mostly recorded at thegrassland sites; when these become bare during drought,the species would still be fairly conspicuous, so the changesare thought to be real, and the birds most likely move todenser shrubland habitat during drought. Possibly, with time,the great majority of species in the Kalahari will at one oranother time or place be found to undertake some (local)movements. For most of the other species, there is a gooddeal of literature (see Tables 1–4) confirming that theyindeed undertake movements during droughts.

Not surprisingly, the grasslands, which have the lowestvegetation structural diversity, and during drought have thelargest proportional loss of structure in the vegetation, alsolost the most birds during the drought. This was evident atthe worst hit area (Sekoma) in the southern Kalahari. Birdpopulations at Kutse in the central Kalahari, on the otherhand, where there was a carry-over of very abundant rainsthe previous season, remained much more stable withimportant influxes of species (e.g. Chestnut-vented Tit-bab-bler). The particular situation of the Red-faced Mousebirdsconcentrating during the drought here on Grewia berries hasbeen dealt with separately (Herremans and Herremans-Tonnoeyr 1994).

Probably many species that are forced to leave an areathrough drought explore the Kalahari over relatively shortdistances in search of a better patch. The nature of locallyvariable rainfall during dry cycles with localised storms ishelpful in this respect. Even during the worst droughts thereare somewhere greener places where rains have been bet-

Ostrich 2004, 75: 217–227 225

this, but unfortunately nowadays long-term studies are limit-ed by finance or other factors.

My approach had the advantage that several sites atgreat distances could be compared in a short period of time,but the low intensity sampling resulted in low numbers formany species (some 40% of all), precluding any furtherassessment for these at species level. Furthermore, countsin different seasons inevitably have to cope with changes inbird behaviour (territoriality, singing, flocking etc.) and vege-tation-dependent differences in visibility, meaning that evencounts with a strict procedure result at best in semi-quanti-tative data. To convert these to densities has some furtherrisks but, as an indication, it is estimated that in this studyapproximately 35ha were more or less effectively surveyedper transect count. The chance of detecting a bird from astationary point decreases with distance from the observer,and current wisdom and practice for standardisation of tran-sect counts is to calculate densities based on a species-spe-cific detection probability function (see, for example, pro-gramme ‘distance’ at http://www.ruwpa.st-and.ac.uk/dis-tance/). No matter how correct this approach may be in the-ory, in practice variances on density estimates may becomeso large that it is difficult to maintain statistically that anybirds were indeed present at all (see, for example, alsoDean and Milton 2001).

ChangesLiversidge (1966) recorded a drop in the bird breeding pop-ulation of 31% in numbers and 28% in species between adrought and wet year in a moderately drought-sensitive areain the Eastern Cape. The Kalahari data show much largerchanges, 37–81% in numbers, and are more similar to thoseobtained between a wet and dry cycle in the more aridsouthern Karoo: 70% of bird numbers and 63% of species(Dean and Milton 2001). Maclean (1970b) considered morethan half the bird species in the Kalahari to be nomadic. Inthis study, some 60% of the species with sufficiently largesamples showed considerable changes from dry to wet sea-son or from wet season to drought. Such changes may,however, have several causes: (1) mere chance effects dur-ing sampling — the present programme with counts on asingle day covering only c. 35ha may be particularly sensi-tive to such effects. Low density species, particularly whenlikely to flock at some stage during the year are especially atrisk; (2) changes in conspicuousness and visibility; (3) a realdecline or increase in numbers, which can be the result ofmortality or breeding; (4) emigration or immigration. The firsttwo points reflect sampling variation and error while the lat-ter two are more interesting for population dynamics, butunfortunately with the present method mortality and emigra-tion cannot be distinguished. Breeding was limited duringthe dry summer of 1992, so reproductive output will hardlyhave had a major impact on numbers. Chance effects haveprobably mostly been avoided by selecting only the 60% ofspecies with larger samples. Changes in conspicuousnessmay to some extent affect the data for many species, but inthe final selection (Tables 2–5) it appears that only forCrested Francolin and Barred Wren-warbler Calamonastesfasciolatus might this be the principal factor for the recordedchanges. Both species are very unobtrusive when not call-

ing, and the numbers in the samples are fairly low.Furthermore, for neither of the species did I find literaturereferences indicating the possibility of movements. Similarconsideration could be made for Tinkling Cisticola Cisticolarufilatu, Rufous-naped Lark Mirafra africana and Brown-crowned Tchagra Tchagra australis, except that here goodnumbers were recorded during the 1991 dry season as well,making the decline probably real. Furthermore, the cisticolaresponds well to Pearl-spotted Owlet calls and is thus rela-tively easy to record; it also fits the pattern of congenericspecies, which all lose the grassy component of their habitatduring drought in the Kalahari. I consider it unlikely thatthese species suffered such a high mortality rate so sooninto a drought period; the drought continued well into 1994,and if mortality would already have such an impact duringthe first months of a drought, there would not be many leftduring prolonged droughts. I suggest that these speciesshould be watched more closely in future for (local) move-ments. The Ant-eating Chat Myrmecocichla formicivora isanother species for which I did not find literature evidencefor movements, but because it is conspicuous and respondswell to Pearl-spotted Owlet calls, the counts are reliable, andmovements are a likely explanation. The korhaans also forman intriguing case. Red-crested Korhaan Lophotis ruficristacan be very unobtrusive in dense shrubland when not call-ing, and I accept that I failed to record them during thedrought when not calling. However, Tree (1972), duringmonths of observation from a bush camp, also noted thatthis species became much less common in the northernKalahari in a severe drought. It is likely that some move intonearby moister woodlands during dry cycles. Northern BlackKorhaans Afrotis afraoides were mostly recorded at thegrassland sites; when these become bare during drought,the species would still be fairly conspicuous, so the changesare thought to be real, and the birds most likely move todenser shrubland habitat during drought. Possibly, with time,the great majority of species in the Kalahari will at one oranother time or place be found to undertake some (local)movements. For most of the other species, there is a gooddeal of literature (see Tables 1–4) confirming that theyindeed undertake movements during droughts.

Not surprisingly, the grasslands, which have the lowestvegetation structural diversity, and during drought have thelargest proportional loss of structure in the vegetation, alsolost the most birds during the drought. This was evident atthe worst hit area (Sekoma) in the southern Kalahari. Birdpopulations at Kutse in the central Kalahari, on the otherhand, where there was a carry-over of very abundant rainsthe previous season, remained much more stable withimportant influxes of species (e.g. Chestnut-vented Tit-bab-bler). The particular situation of the Red-faced Mousebirdsconcentrating during the drought here on Grewia berries hasbeen dealt with separately (Herremans and Herremans-Tonnoeyr 1994).

Probably many species that are forced to leave an areathrough drought explore the Kalahari over relatively shortdistances in search of a better patch. The nature of locallyvariable rainfall during dry cycles with localised storms ishelpful in this respect. Even during the worst droughts thereare somewhere greener places where rains have been bet-

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ter or are better captured in the landscape (drainage lines);birds just have to find them. Dean and Milton (2001) alsopoint out the importance of drainage lines with richer vege-tation for local movements at landscape level, particularlyduring droughts. Curiously enough, the largest changes andmost profound impact on avian diversity come from thenorthern periphery of the Kalahari (Nata and Phuduhudu).These sites are closest to reliably more lush and moistervegetations and more birds seem to have adapted here toregular tactics of moving in and out. The northern Kalaharihas the most distinct bird community during a wet cycle,caused by an influx of species from the moister woodlandsfurther north, but at the start of droughts, these more mesicelements move out again, and the bird community becomesentirely Kalahari (Figure 5), also enhanced by influxes fromtypical Kalahari birds (e.g. Table 5: Scaly-feathered Finch,Violet-eared Waxbill). Consequently, the typical Kalahari birdcommunity expands its range during drought into the moisterperiphery. Remarkably, even some of the more typicalKalahari birds appear to be more mobile in the northern andmore lush part of the Kalahari, and undergo unexpectedlysubstantial decreases during drought at Phuduhudu(Laughing Dove Streptopelia senegalensis, Cape Turtle-dove Streptopelia capicola, Namaqua Dove Oena capensis,Acacia Pied Barbet Tricholaema leucomelas, Fawn-coloured Lark, Chestnut-vented Tit-babbler, Kalahari Scrub-robin, Marico Flycatcher, Black-chested Prinia, Brown-crowned Tchagra). Probably because better habitat can soreliably be found somewhere relatively close to the northernperiphery of the Kalahari, it pays off for these populations toleave their territories and go and look for greener pasturesat a lower threshold of drought. A similar effect could alsohappen at the eastern periphery of the Kalahari with move-ments into the eastern Hardveld of Botswana, but the sitesin this study were not optimally chosen to demonstrate this(although the influx of species into Kgoro in the wet seasonis of note in this context).

Acknowledgements — I am grateful to the referees Ara Monadjemand Stephanie Tyler for their improvements.

References

Anonymous 1989. List of migrant bird species occurring inBotswana. Babbler 18: 51–52

Ashby N 1992. Some records from Nata. Babbler 24: 30–31Bishop D, Borello WD and Herremans M 1992. Interesting and

unusual sightings. Babbler 24: 59–61Borello WD 1992. An incidence of mass sunbird migration in north-

ern Botswana. Babbler 23: 18–21Brewster CA 1991. Birds of the Gumare area, north-west

Botswana. Babbler 21&22: 12–61Brewster CA 1992. Notes on the effects of drought on birds in the

Sefhare area from February–September 1992. Babbler 24: 31–32Brewster CA 1993. Notes on the birds of the Tswapong South area.

Babbler 25: 6–20Brewster CA 1996. Fluctuations in bird numbers on fallow land in

the Sefhare area of eastern Botswana. Babbler 31: 17–21Brooke RK 1994. Sub-speciation studies and our knowledge of

migration and other movements in southern African birds. Ostrich65: 49–53

Cain AJ and Harrison GA 1958. An analysis of the taxonomists’

judgement of affinity. Proceedings of the Zoological Society ofLondon 131: 85–98

Dawson JL 1975. The birds of Kutse Game Reserve. BotswanaNotes and Records 7: 141–150

Dean WRJ and Milton SJ 2001. The density and stability of birdsin shrubland and drainage line woodland in the southern Karoo,South Africa. Ostrich 72: 185–192

Gower JC 1985. Measures of similarity, dissimilarity and distance.In: Johnson NL, Kotz S and Read CB (eds) Encyclopaedia ofStatistics, Vol. 5. pp 397–405. Wiley, New York

Harrison JA, Allan DG, Underhill LG, Herremans M, Tree AJ,Parker V and Brown CJ 1997. The Atlas of Southern AfricanBirds, Vols 1 & 2. BirdLife South Africa, Johannesburg

Hawker R 2003. More Kalahari species in Maun. Babbler 43: 47Heck KL, Van Belle G and Simberloff D 1975. Explicit calculation

of the rarefaction diversity measurement and the determination ofsufficient sample size. Ecology 56: 1459–1461

Herremans M 1992. Indirect evidence for the existence of move-ments of sunbirds in Botswana. Babbler 24: 4–9

Herremans M 1993. Seasonal dynamics in sub-Kalahari bird com-munities with emphasis on migrants. In: Wilson RT (ed) Birds andthe African Environment. Proceedings of the 8th Pan-AfricanOrnithological Congress. pp 555–564. RMCA, Tervuren

Herremans M 1994a. Fifteen years of migrant phenology records inBotswana: a summary and prospects. Babbler 28: 47–68

Herremans M 1994b. Partial migration in the Masked WeaverPloceus velatus in south-eastern Botswana. Ostrich 65: 79–85

Herremans M and Herremans-Tonnoeyr D 1994. Evidence for theexistence of movements in the Red-faced Mousebird Coliusindicus in the Kalahari. Babbler 26–27: 7–10

Koen JH 1992. Medium-term fluctuations of birds and their poten-tial food resources in the Knysna forest. Ostrich 63: 21–30

Liversidge R 1966. Fluctuations in a breeding population in theEastern Cape. Ostrich supplement 6: 419–424

Liversidge R 1980. Seasonal changes in the use of avian habitat insouthern Africa. Acta Congressus Internationalis Ornithologici1980(2): 1019–1024

Liversidge R 1984. Changes in the avian population of the KalahariNational Park. In: Ledger J (ed) Proceedings of the 5th Pan-African Ornithological Congress. pp 163–177. SAOS,Johannesburg

Liversidge R 1996. A new species of pipit in southern Africa.Bulletin of the British Ornithologists’ Club 116: 211–215

Liversidge R 2002. The Kimberley pipit: a new African species.Bulletin of the British Ornithologists’ Club 122: 93–109

Lloyd P 1999. Rainfall as a breeding stimulus and clutch size deter-minant in South African arid-zone birds. Ibis 141: 637–643

Maclean GL 1970a. The breeding seasons of birds in the south-western Kalahari. Ostrich Supplement 8: 179–192

Maclean GL 1970b. An analysis of the avifauna of the southernKalahari Gemsbok National Park. Zoologica Africana 5: 249–273

Maclean GL 1970c. The biology of the larks (Alaudidae) of theKalahari sandveld. Zoologica Africana 5: 7–39

Maclean GL 1987. Seasonal changes in the bird life of north-east-ern Botswana. Bokmakierie 39: 109–111

Maclean GL 1993. Roberts’ Birds of Southern Africa. 6th edn. JohnVoelcker Bird Book Fund, Cape Town

Magurran AE 1988. Ecological diversity and its measurement.Croom Helm, London

Monadjem A 2001. Population fluctuations of birds in Acaciasavanna in Swaziland. Durban Museum Novitates 26: 6–9

Monadjem A 2004. Population fluctuations of birds in riverine forestand broadleaved woodland in Swaziland. Durban MuseumNovitates 29: 50–56

Muller M 2002. Influx of Kalahari specials and other bird news inMaun. Babbler 41: 39–40

Herremans226

ter or are better captured in the landscape (drainage lines);birds just have to find them. Dean and Milton (2001) alsopoint out the importance of drainage lines with richer vege-tation for local movements at landscape level, particularlyduring droughts. Curiously enough, the largest changes andmost profound impact on avian diversity come from thenorthern periphery of the Kalahari (Nata and Phuduhudu).These sites are closest to reliably more lush and moistervegetations and more birds seem to have adapted here toregular tactics of moving in and out. The northern Kalaharihas the most distinct bird community during a wet cycle,caused by an influx of species from the moister woodlandsfurther north, but at the start of droughts, these more mesicelements move out again, and the bird community becomesentirely Kalahari (Figure 5), also enhanced by influxes fromtypical Kalahari birds (e.g. Table 5: Scaly-feathered Finch,Violet-eared Waxbill). Consequently, the typical Kalahari birdcommunity expands its range during drought into the moisterperiphery. Remarkably, even some of the more typicalKalahari birds appear to be more mobile in the northern andmore lush part of the Kalahari, and undergo unexpectedlysubstantial decreases during drought at Phuduhudu(Laughing Dove Streptopelia senegalensis, Cape Turtle-dove Streptopelia capicola, Namaqua Dove Oena capensis,Acacia Pied Barbet Tricholaema leucomelas, Fawn-coloured Lark, Chestnut-vented Tit-babbler, Kalahari Scrub-robin, Marico Flycatcher, Black-chested Prinia, Brown-crowned Tchagra). Probably because better habitat can soreliably be found somewhere relatively close to the northernperiphery of the Kalahari, it pays off for these populations toleave their territories and go and look for greener pasturesat a lower threshold of drought. A similar effect could alsohappen at the eastern periphery of the Kalahari with move-ments into the eastern Hardveld of Botswana, but the sitesin this study were not optimally chosen to demonstrate this(although the influx of species into Kgoro in the wet seasonis of note in this context).

Acknowledgements — I am grateful to the referees Ara Monadjemand Stephanie Tyler for their improvements.

References

Anonymous 1989. List of migrant bird species occurring inBotswana. Babbler 18: 51–52

Ashby N 1992. Some records from Nata. Babbler 24: 30–31Bishop D, Borello WD and Herremans M 1992. Interesting and

unusual sightings. Babbler 24: 59–61Borello WD 1992. An incidence of mass sunbird migration in north-

ern Botswana. Babbler 23: 18–21Brewster CA 1991. Birds of the Gumare area, north-west

Botswana. Babbler 21&22: 12–61Brewster CA 1992. Notes on the effects of drought on birds in the

Sefhare area from February–September 1992. Babbler 24: 31–32Brewster CA 1993. Notes on the birds of the Tswapong South area.

Babbler 25: 6–20Brewster CA 1996. Fluctuations in bird numbers on fallow land in

the Sefhare area of eastern Botswana. Babbler 31: 17–21Brooke RK 1994. Sub-speciation studies and our knowledge of

migration and other movements in southern African birds. Ostrich65: 49–53

Cain AJ and Harrison GA 1958. An analysis of the taxonomists’

judgement of affinity. Proceedings of the Zoological Society ofLondon 131: 85–98

Dawson JL 1975. The birds of Kutse Game Reserve. BotswanaNotes and Records 7: 141–150

Dean WRJ and Milton SJ 2001. The density and stability of birdsin shrubland and drainage line woodland in the southern Karoo,South Africa. Ostrich 72: 185–192

Gower JC 1985. Measures of similarity, dissimilarity and distance.In: Johnson NL, Kotz S and Read CB (eds) Encyclopaedia ofStatistics, Vol. 5. pp 397–405. Wiley, New York

Harrison JA, Allan DG, Underhill LG, Herremans M, Tree AJ,Parker V and Brown CJ 1997. The Atlas of Southern AfricanBirds, Vols 1 & 2. BirdLife South Africa, Johannesburg

Hawker R 2003. More Kalahari species in Maun. Babbler 43: 47Heck KL, Van Belle G and Simberloff D 1975. Explicit calculation

of the rarefaction diversity measurement and the determination ofsufficient sample size. Ecology 56: 1459–1461

Herremans M 1992. Indirect evidence for the existence of move-ments of sunbirds in Botswana. Babbler 24: 4–9

Herremans M 1993. Seasonal dynamics in sub-Kalahari bird com-munities with emphasis on migrants. In: Wilson RT (ed) Birds andthe African Environment. Proceedings of the 8th Pan-AfricanOrnithological Congress. pp 555–564. RMCA, Tervuren

Herremans M 1994a. Fifteen years of migrant phenology records inBotswana: a summary and prospects. Babbler 28: 47–68

Herremans M 1994b. Partial migration in the Masked WeaverPloceus velatus in south-eastern Botswana. Ostrich 65: 79–85

Herremans M and Herremans-Tonnoeyr D 1994. Evidence for theexistence of movements in the Red-faced Mousebird Coliusindicus in the Kalahari. Babbler 26–27: 7–10

Koen JH 1992. Medium-term fluctuations of birds and their poten-tial food resources in the Knysna forest. Ostrich 63: 21–30

Liversidge R 1966. Fluctuations in a breeding population in theEastern Cape. Ostrich supplement 6: 419–424

Liversidge R 1980. Seasonal changes in the use of avian habitat insouthern Africa. Acta Congressus Internationalis Ornithologici1980(2): 1019–1024

Liversidge R 1984. Changes in the avian population of the KalahariNational Park. In: Ledger J (ed) Proceedings of the 5th Pan-African Ornithological Congress. pp 163–177. SAOS,Johannesburg

Liversidge R 1996. A new species of pipit in southern Africa.Bulletin of the British Ornithologists’ Club 116: 211–215

Liversidge R 2002. The Kimberley pipit: a new African species.Bulletin of the British Ornithologists’ Club 122: 93–109

Lloyd P 1999. Rainfall as a breeding stimulus and clutch size deter-minant in South African arid-zone birds. Ibis 141: 637–643

Maclean GL 1970a. The breeding seasons of birds in the south-western Kalahari. Ostrich Supplement 8: 179–192

Maclean GL 1970b. An analysis of the avifauna of the southernKalahari Gemsbok National Park. Zoologica Africana 5: 249–273

Maclean GL 1970c. The biology of the larks (Alaudidae) of theKalahari sandveld. Zoologica Africana 5: 7–39

Maclean GL 1987. Seasonal changes in the bird life of north-east-ern Botswana. Bokmakierie 39: 109–111

Maclean GL 1993. Roberts’ Birds of Southern Africa. 6th edn. JohnVoelcker Bird Book Fund, Cape Town

Magurran AE 1988. Ecological diversity and its measurement.Croom Helm, London

Monadjem A 2001. Population fluctuations of birds in Acaciasavanna in Swaziland. Durban Museum Novitates 26: 6–9

Monadjem A 2004. Population fluctuations of birds in riverine forestand broadleaved woodland in Swaziland. Durban MuseumNovitates 29: 50–56

Muller M 2002. Influx of Kalahari specials and other bird news inMaun. Babbler 41: 39–40

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

23:

26 2

2 N

ovem

ber

2014

Ostrich 2004, 75: 217–227 227

Pausch E 1998. Birds of Kutse Game Reserve, Botswana. Babbler33: 5–16

Penry H 1994. Bird Atlas of Botswana. University of Natal Press,Pietermaritzburg

Simberloff D 1972. Properties of the rarefaction diversity measure-ment. American Naturalist 106: 414–418

StatSoft, Inc. 2001. Statistica 6.0 (data analysis software system).StatSoft, Tulsa

Symes CT, Wirminghaus JO and Downs CT 2002. Species rich-ness and seasonality of forest avifauna in three South AfricanAfromontane forests. Ostrich 73: 106–113

Tree AJ 1972. Ornithological comparison between differing dry sea-sons at a pan in Botswana. Ostrich 43: 165–168

Tyler SJ 2001. Local movements by Red-faced Mousebirds Coliusindicus at Ruretse. Babbler 38: 17–18

Wilson JR 1984. The avifauna of the Lobatse area, south-eastBotswana. Babbler 8: 17–45

Received May 2004, accepted June 2004Editor: MD Anderson

Ostrich 2004, 75: 217–227 227

Pausch E 1998. Birds of Kutse Game Reserve, Botswana. Babbler33: 5–16

Penry H 1994. Bird Atlas of Botswana. University of Natal Press,Pietermaritzburg

Simberloff D 1972. Properties of the rarefaction diversity measure-ment. American Naturalist 106: 414–418

StatSoft, Inc. 2001. Statistica 6.0 (data analysis software system).StatSoft, Tulsa

Symes CT, Wirminghaus JO and Downs CT 2002. Species rich-ness and seasonality of forest avifauna in three South AfricanAfromontane forests. Ostrich 73: 106–113

Tree AJ 1972. Ornithological comparison between differing dry sea-sons at a pan in Botswana. Ostrich 43: 165–168

Tyler SJ 2001. Local movements by Red-faced Mousebirds Coliusindicus at Ruretse. Babbler 38: 17–18

Wilson JR 1984. The avifauna of the Lobatse area, south-eastBotswana. Babbler 8: 17–45

Received May 2004, accepted June 2004Editor: MD Anderson

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

23:

26 2

2 N

ovem

ber

2014