Further studies of wintering crag martins

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Further studies of winteringcrag martinsN. Elkins a & B. Etheridge ba 10 Oakbank Place, Elgin, Morayshire, IV30 2LZb 1 Thornhill Crescent, Forres, Morayshire, IV36OHVPublished online: 11 Apr 2011.

To cite this article: N. Elkins & B. Etheridge (1977) Further studiesof wintering crag martins, Ringing & Migration, 1:3, 158-165, DOI:10.1080/03078698.1977.9673720

To link to this article: http://dx.doi.org/10.1080/03078698.1977.9673720

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158

Further Studies of Wintering Crag Martins

by N. Elkins and B. Etheridge

The behaviour of Crag Martins Hirundo rupestris in winter quarters at Gibraltar has beendescribed previously by Elkins and Etheridge (1974). Trapping and ringing at this largewinter roost were continued by BE during a further winter, and a total of 46 visits weremade during the months October 1974 to March 1975. Methods and description of thehabitat and roost may be found in the previous paper but some of the earlier results givenin the appendix to that paper are now superseded by the fresh data obtained.

PLUMAGESBirds were separated into juveniles (first winter birds) and adults (all others).

Separation was easier at the beginning of the winter when adult plumage was new ormoulting, with uniform brown-grey upperparts, and all birds in wing and tail moult wereadults, with one exception. Early in the season, the majority of juveniles showed adistinctive plumage, in which the buff-edged feathers of the upperparts give a scalyappearance. Juveniles which had moulted these feathers could be distinguished by thepresence of whitish-buff edges to the tertials and greater coverts, and also by the abrasionto the tips of the remiges and rectrices in early winter when adult feathers were hew. Onlyin late February and March, when most young birds had completed the post-juvenilebody moult, could abrasion of these pale feather edgings cause confusion with adults.There was no sexual dimorphism in plumage colouration.

During the two winters of trapping, measurements were taken of the length of the whitetail spots to determine their use as ageing criteria. There are normally four on each side,on rectrices 2 to 5, although there were examples of as few as two spots and as many asfive. That on the 3rd or 4th rectrix is the longest. Of 154 juveniles, the mean length of the

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20

16

16

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12

10

8

6

Juveniles

LJ

Adults

11

11

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20 10 10 20 30

Figure 1. Percentage distributions of length of longest tail spots of Crag Martins.(Ringing and Migration 1: 158-165, 1977)

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CRAG MARTINS 159

longest spot was 11.3mm ±2.1, whilst that of 84 adults was 14.0mm ± 1.8. There washowever considerable overlap (Figure 1). Three juveniles retrapped the following winterhad increased this length by 3mm, 3mm and 4mm respectively.

POPULATION AND MIGRATION1,332 Crag Martins were trapped and ringed between 11 October 1974 and 27 March1975, and 60 birds ringed during the previous winter were retrapped. The winteringpopulation had increased once again from previous years. Direct counts of birds arrivingat the roost revealed an early January peak of 3,100.

A possible large passage was observed at dusk on 5 November 1974, when 1,500 birdsdisappeared southwards towards the Strait of Gibraltar. A roost was present in themountains of North Morocco, only about 30km SSW of Gibraltar, which the birds maysubsequently have utilised (J. Pineau in liti). A temporary reduction at the roostimmediately after this date, was followed by a steady increase, reaching a peak by lateDecember. No other passage was observed. It is not known whether there was1 anymovement between this roost and adjacent Spanish roosts (if any existed).

53 316 223 113 111 243 69 147 77 100 70

60

20

Oct Kov Dec Jan Feb Mar

Figure 2. Percentage of adults in the wintering population of Crag Martins atGibraltar. Sample sizes shown above.

Figure 2 shows low proportions of adults in autumn and the second half of March,indicating that the older birds had a shorter wintering period than juveniles, probablyreturning earlier to breeding sites. The presumed early exit of adults in March wasaccompanied by a noticeable reduction in the size of the roost in mid month, and onlythree adults ringed after 7 February were caught again. The lack of retraps of Octoberbirds suggested that the majority were on passage, with the resident population arriving inNovember and December, as birds ringed in these months gave a relatively highsubsequent retrap rate during the remainder of the winter. Migrant adults may have beenpresent in late January, as no adults ringed in the second half of the month wereretrapped. The first major period of bad weather at Gibraltar began on 11 January, andabnormally fine weather in November and December may have caused the increase in the

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160 RINGING AND MIGRATION

size of the roost over the previous winter, with fewer birds moving on into North Africa.Feeding range was indicated by four winter recoveries in the Spanish hinterland within

a 15km radius of the roost, although it cannot be certain that all these were roosting atGibraltar at the time of recovery. One of these was a November juvenile recovered in thefollowing March. The others were all January-ringed, one juvenile recovered two dayslater and the others, one juvenile and one adult, recovered in the following winter inNovember and January respectively. There were also two distant recoveries of adults inthe same area of NE Spain, some 550km from Gibraltar. The first was ringed inNovember and recovered the following June in Castellon province. It was found 600 to800m above sea-level and was almost certainly breeding. The second, a February-ringedbird, was recovered in late October in Valencia province. It was found in low land about65km from the coast.

MOULTAll individuals were inspected for moult. BTO moult cards were completed in thestandard manner(Snow 1967) for 129 adults and one juvenile in wing moult. Tail moultwas recorded when present, and although body moult was noted in many birds, catch sizefrequently precluded close study of moult other than of remiges and rectrices.

Adults. All adults arriving in early October were in advanced moult and by the secondweek of November, 50% had completed primary moult. Although several birds in lateNovember had a primary moult score of less than 40, 95% had fully grown primaries bythe first week in December. Secondary moult was about two-thirds complete in mid-October and generally finished by mid-December. Subsequently twenty birds (7.6%)showed suspended moult of the inner secondaries, usually the 5th and 6th. These

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30 5 10 15 20 25 30 sss

Figure 3. Relationship between primary and secondary moult scores of Crag Martins.Small dots, 1 bird; middle-sized dots, 2-4 birds; large dots, 4+ birds.

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CRAG MARTINS 161

appeared to be replaced in late winter. The tertials were new on all except three earlywinter birds with suspended moult. Tail moult was rather irregular, often asymmetrical,and mostly completed by December. Occasionally, several feathers were moultedtogether, and as a general rule, the outer rectrices were shed before the 5th, as in theSwallow Hirundo rustica (Medway 1973). The relationships of primary moult tosecondary and tail moult in the late stages are shown in Figures 3 and 4. Wing covertswere invariably new, as these were moulted before arrival in October. Body moult waswell advanced on arrival and generally complete by early December, although occasionaladults with old body feathers were caught in late winter.

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3020 30 60 tail

Figure 4. Relationship between primary and tail moult scores of Crag Martins. Smalldots, 1 bird: middle-sized dots, 2-4 birds; large dot, 4+ birds.

Juveniles. Post-juvenile moult was partial. Only one of 946 juveniles showed wingmoult and none showed tail moult. On 13 December a bird was trapped showing six newinner primaries, the innermost two on each wing, plus the 3rd on one side and the 4th onthe other. All other remiges were old. Body moult was in evidence throughout the winter,and appeared to be continuous and slow in many birds. Several individuals showingmoult in November were still moulting in February and March, and many birds stillshowed scaly upperparts in late winter (Figure 5). Those individuals showing no scalyfeathers had either completed or nearly completed (over two-thirds complete) bodymoult. Head feathers were the last feathers to be moulted. There were several instancesthroughout the winter of partial moult of wing and tail coverts, but not greater coverts.

MEASUREMENTSWing-lengths of both age groups are shown in Table 1. The overall mean was identical

to that given for the previous winter. However, further experience in ageing allowed acomparison between adult and juvenile birds, showing the adult wing to be significantlylonger than that of the juvenile. A small sample of twelve adults in their third or laterwinter, i.e. those aged as adults in the previous winter and retrapped in 1974/ 75, showed ahigh mean wing length of 136.2mm ± 1.98, significantly longer than that of the remainderof the population (p -^ 0.005). These older birds had increased their wing-length by a

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162 RINGING AND MIGRATION

60

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Oct Nov Dec Jan Feb >!ar

Figure 5. Proportion of juvenile Crag Martins at Gibraltar with unmoulted 'scaly'upperparts.

mean of 1.25mm between winters. Similarly, 34 birds originally ringed as juvenilesshowed a mean increase of 1.33mm by the next winter.

Mean tail length in 1974/75 was 55.0mm compared with 51.7mm in the previouswinter. This discrepancy was partly attributable to the different periods over whichmeasurements were taken. In 1973/74, all measurements were taken in March, whereas in1974/75, most were taken in October to December, with none in March. Tails sufferedconsiderable abrasion during the winter. In one extreme case, a juvenile had a very worntail of length 43mm in January 1974, whjle its fresh tail-length the following Novemberwas 55m. As with wing-length, the adult tail was significantly longer than that of thejuvenile (p < 0.001,Table 1). The biomodal distribution of tail-length found in the winterof 1973/74 and attributed to sexual dimorphism is therefore now recognised as an agedifference. No bimodality was found in the separate adult and juvenile measurements.

TABLE I. WING AND TAIL LENGTH OF CRAG MARTINS

Wing

Tail

NumberMean (mms)s.d.Range

NumberMean (mms)s.d.Range

Adult391

134.02.82

125-142

4255.81.26

53-59

Juvenile946

132.82.89

124-141

7354.61.48

52-58

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CRAG MARTINS 163

WEIGHTSIn late winter the broad relationship of weight and air temperature was confirmed

(Elkins and Etheridge 1974), but in autumn and early winter, other influences dominatedweight changes.

The relatively low October weights (Table II) occurred after the passage from breedinggrounds and whilst moult was still in progress in the majority of adults. In November,with moult being completed, weights rose considerably, doubtless through theaccumulation of fat. Many birds at this time had large deposits of fat in the tracheal pit andon the belly. Weight changes shown by retrapped birds were of the same order as thosefound in the previous winter. Of 39 November-ringed birds which were retrapped inFebruary and March, 9 had lost over 20% of their original weight and the maximum losswas 39%. The low weight in March may partly have reflected the presence of newlyarrived migrants from North Africa. A lean juvenile trapped whilst feeding on 27 Marchweighed only 15.7g.

TABLE II. MEAN WEIGHTS (GMS) OF CRAG MARTINS AT GIBRALTAR.ADULTS AND JUVENILES COMBINED

1974/75Dawn catchesDusk catches

Oct22.622.9

Nov25.627.1

Dec24.525.5

Jan23.824.5

Feb24.223.4

Mar20.420.5

Comparisons of weights of different groups within the whole population revealed thatjuveniles weighed some 5 to 10% less than adults (see Figure 6). There were too fewexamples to perceive any difference in weight between moulting and non-moultingadults but this was not so in the juvenile population. Weights of birds at the height ofbody moult were compared with those in advanced stages or completed, i.e. those with noscaly upperparts. The latter were consistently heavier than the former. 13 samplescomprising 10 or more of each group showed differences ranging from O.lg to 1.8g(upto8%).

Of the birds ringed in 1973/74, 8.6% of adults and 9.5% of juveniles were retrapped in1974/ 75. There was no evidence that initial weight affected survival, as similar numbers oflight and heavy birds were amongst those retrapped in the following winter.

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a a aS •

o •D

D •

Oct I Nov I Dec ' Jan • Feb ' Ear

Figure 6. Weight of juvenile Crag Martins at Gibraltar shown as a percentage of theweight of adults in the same sample. Closed squares, dusk samples; open squares,

dawn samples.

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164 RINGING AND MIGRATION

DISCUSSIONDue to the extremely advanced state of moult on arrival, it is not possible to give any

definite data on its duration. However, with adult moult almost complete by October,onset must occur during the breeding season, and continue through the migration period.Cramp (1970) quotes moult to be most frequent in July and August, but lasting from Juneto November. Plate 40, accompanying this paper, shows an adult apparently in the firststages of moult, with a primary moult score of about 10. This bird was photographed inPortugal on 17 June. At this point, the nest was being lined, and by 25 June eggs werebeing incubated (Dr K. J. Carlson in tin).

The Crag Martin wintering in Europe may be unable to rely on adequate feedingconditions for a winter moult. As in other species which need continuous full power offlight such as the Swift Apus apus or raptors, moult is necessarily protracted (Harrison1964). Thus it may have to begin early. Resident or short-range migrant Swallows fromthe southern parts of the breeding range (Egypt to the Himalayas) also begin moult asearly as June and July (Stresemann and Stresemann quoted by Pimm 1972), and earlymoult is also known from Swallows in southern Spain (Pimm 1970). The long-distancemigratory "Swallow populations moult in winter quarters in Africa, although some adultsbegin moult before migration (Mead 1975), presumably then suspending moult untilarrival in winter quarters. Another aerial species, the Alpine Swift Apus melba, shares asimilar breeding range and habitat with the Crag Martin, and has a similar moultingperiod. Moreau (1972) considered the Alpine Swift's early moult to be connected with itslate departure from breeding grounds. Both this species and the Crag Martin leave forwinter quarters some 6 weeks later than the Swift and the Swallow.

The post-juvenile moult of most long-distance migrant hirundines, which is complete,occurs in winter quarters along with the adults (Snow 1967). However, the juvenile CragMartin only undergoes a partial moult in its first winter. Those juveniles completingmoult by early winter may be from early broods, having moulted relatively quickly duringoptimum conditions. Those showing a protracted moult throughout the winter, whenenvironmental conditions are more severe, may have fledged later in the summer.

The difference in tail length between the two winters was attributed to abrasion on therough surfaces of cave roosts. Abrasion may be at a maximum when roosts are used forlonger periods during poor weather (Elkins and Etheridge 1974), so its degree could varywith the severity of the winter. The winter of 1974/75 was abnormally dry and slightlywarmer than the previous one. The major abrasion in 1973/74, noticed in someindividuals as early as January could be linked with the bad weather of early winter, whenrain fell on 34% of the days of November and December 1973. In contrast, the followingwinter had only one wet day during the same period (data from the Meterological Office,Gibraltar).

ACKNOWLEDGEMENTSWe wish to thank H. van Gils and J. C. Finlayson for assistance with field work.

Acknowledgement is due to the Meteorological Office for permission to publish weather data. Weare indebted to Dr K. J. Carlson for providing information on his photographs in Cramp (1970) andto Dr Ian Newton for valuable comments and advice.

SUMMARYFurther studies of plumage, population changes and weights of wintering Crag Martins at

Gibraltar are described. Biometrical data are given and differences between adult and juvenile birdsare shown. Certain results in our previous paper are corrected. Moult is described and related to thespecies' migratory habits.

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CRAG MARTINS 165

REFERENCESCRAMP, S. 1970. Studies of less familiar birds. 159. Crag Martin. Brit. Birds. 63: 239-243.ELKINS, N. and ETHERIDGE, B. 1974. The Crag Martin in winter quarters at Gibraltar. Brit. Birds. 67: 376-387.HARRISON, J. M. 1964. Moult. In Thomson A. L. (ed.). A New Dictionary of Birds. London.MEAD, C. J. 1975. Juvenile hirundines starting primary moult in Europe. Ring. and Migr., 1:57.MEDWAY, LORD. 1973. A ringing study of migratory Barn Swallows in west Malaysia, Ibis. 115: 60-86.MOREAU, R. E. 1972. The Palaearctic-African Bird Migration Systems. London and New York.PIMM, S. L. 1970. Swallows in wing moult in southern Spain. Bird Study, 17:49-51.

1972. Moult in the Swallow, Bird Study, 19, 116.SNOW, D. W. 1967. A Guide to Moult in British Birds. BTO Field Guide No. 11. Tring.

N. Elkins. 10 Oakbank Place, Elgin, Morayshire, IV30 2LZ.B. Etheridge, 1 Thornhill Crescent, Forres, Morayshire, IV36 OHV.

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