Two complete migration cycles of an adult Hobby tracked by

The Hobby Falco subbuteo breeds acrossEurope and Asia and is a long-dis-tance, trans-equatorial migrant. Euro-

pean (and probably Asian) birds winter incentral and southern Africa (Brown et al.1982; Pepler 1993; Mendelsohn 1997) and

the species’ main wintering area is believed tobe the Zambezi Basin between 10° and 20°S(Chapman 1999). According to Pinto (1983)and Dean (2000), the Hobby is anuncommon migrant in Angola from Octoberuntil March, in Acacia and Miombo wood-

2 © British Birds 104 • January 2011 • 2–15

Two completemigration cycles of an adult Hobby tracked by satelliteBernd-Ulrich Meyburg, Paul W. Howey, Christiane Meyburg and Klaus Dietrich FiuczynskiAbstract A prototype of the smallest satellite transmitter produced so far,weighing just 5 g, was fitted to an adult Hobby Falco subbuteo in Germany in August2008. Two autumn and two spring migrations were recorded successfully from theunit carried by this particular Hobby. All four migration routes were to the westof a direct line between breeding site and wintering area. The migration route inspring 2010 was up to 2,150 km farther west than that in autumn 2009, effectivelyforming a ‘migration loop’. This was much less pronounced in 2008/09. The directdistance from the breeding site to the southernmost point reached in Zimbabwein 2008/09 was 10,065 km. The fastest flight speeds on migration were recorded inspring 2010 in Mali and Morocco, when 1,243 km was covered in two days. Also inspring 2010, during migration from Morocco to southern France (1,032 km in twodays), the falcon migrated at night, when a fix was made over the Mediterranean inthe vicinity of Gibraltar. Migration across the Sahara took 4–4.5 days on eachmigration. The West African equatorial rainforest appears to be a significantecological barrier, and the significance of this is discussed. Migration was noticeablyrapid there with distances of up to 580 km flown per day – also partly at night.During both wintering periods the falcon spent the majority of its time in theAngolan Miombo woodlands, but in winter it also travelled large distances: from16th October 2008 to 7th April 2009, the bird covered a total distance of at least9,025 km between identified night roosts. In 2009, the bird spent half the year inthe wintering area, a third on the breeding grounds and the remaining 18% of thetime on migration; i.e. 65% of its time in Africa and 35% in Europe.

This paper is dedicated to Robin Chancellor, who contributed so much to raptor research and conservation byediting the Proceedings of all Birds of Prey World Conferences, and who died in October 2010 (see pp. 42–43).

lands from southern areas north across thecentral plateau to Bié.Very little is known about the Hobby’s

migration. Only a small number of birds areobserved at the well-known bottlenecks suchas Gibraltar. A total of 5,720 Hobbies wereringed in ten European countries between1909 and 1998 (including over 1,000 inBerlin and Brandenburg, Germany), of which203 (3.5%) were subsequently recovered,although none south of the Sahara Desert(Chapman 2002). Since then, we know ofonly two ring-recoveries from Africa south ofthe Sahara. At present, mapping the win-tering areas of long-distance migrants isbased mainly on ring-recoveries, satellitetelemetry, stable-isotope analysis of feathersor other tissues and through the use ofgenetic markers. Satellite tracking using theArgos system (Argos 1996) is now anaccepted technique.

Study site and methodsThe Hobby has been studied in Berlin and itsenvirons for decades (Fiuczynski 1978, 1987,2007; Fiuczynski & Nethersole-Thompson1980). A nest-site in a disused CommonRaven Corvus corax nest in pine trees north-west of Berlin (52°50’N/13°0’E) was in a ter-ritory occupied each year between 2005 and2009, although young fledged from the siteonly in 2005 and 2008. On 9th August 2008,an adult female (weighing 265 g) was caughtat this nest-site, using an adult White-tailedEagle Haliaeetus albicilla as a decoy. TheHobby (which had raised two offspring) wasfitted with a new type of satellite transmitter(Platform Transmitter Terminal, or PTT),which was at that time still in a developmentphase1. The device was solar-powered andweighed 5 g (1.9% of the Hobby’s bodymass); it was attached as a ‘backpack’ using aharness with neck and body loops. Theoverall weight of the harness was approxi-mately 1 g. Satellite data were received through the

Argos satellite-based positioning system.

These data were decoded and processed usingsoftware produced by Microwave Telemetry,Inc. (USA) and displayed via Google EarthPro, ArcView GIS 3.2b (ESRI GIS andMapping Software, USA), and Animal Move-ments Extension to ArcView GIS. To displaymigration routes, only location classes (LCs)3, 2, 1 and 0 were used. LCs of inferior andpoor quality (LC A, B and Z) were mostlyexcluded. The deviations indicated by Argosfor class LC 3 (best quality) are 150 m, LC 2up to 350 m and LC 1 up to 1 km. Unlessstated otherwise, transmitter data are given inco-ordinated universal time. Only whereimportant data points were missing were LCsof lesser quality used in our results.We could not detect any effect of the

transmitter on the Hobby’s behaviour. Thetransmitter was programmed to operate on aduty cycle of 10 hours on/48 hours off. Eco-logical digital Google Earth maps were usedto evaluate the data. They are based on orig-inal publications such as Olson et al. (2001)and DeFries et al. (2000). Where possible, the falcon’s night roosts

were established in order to record habitatuse and changes in location in the winteringarea. As a rule, because of the transmitter’sprogramming, it was possible to localise onlyevery second roost (but most of themthrough several good fixes: LC 1–3). Otherfixes made in daylight hours were disre-garded. The distances between the individualnight roosts were measured and the respec-tive habitat determined by overlaying withdigital maps.The home ranges were determined with

the help of fixed kernel techniques (Worton1989) and the ‘Minimum Convex Polygon’(MCP) method (Kenward 2001; Selkirk &Bishop 2002; Laver & Kelly 2008). The evalu-ation of the fixes was made using the home-range extension for ArcView from Rodgers &Carr (1998) as well as the home-range toolsfor ArcGis from Rodgers et al. (2007). Amongother features, this computer programpermits calculation of the MCP. The Floating

3British Birds 104 • January 2011 • 2–15

Migration of an adult Hobby tracked by satellite

1 Dimensions of the transmitter were 24 x 14 x 7.5 mm – antenna hard nylon-coated flexible-strandedmarine-grade stainless steel, 178 mm long, potted in high-grade epoxy resin – with sensors to measure tem-perature and its own battery voltage with each parameter relayed by Argos on each transmission. Micro-processor-controlled battery charging with a power output of 200mW and an operating frequency of401.650 MHz +/- 36 kHz.

Amean method (‘proximity to recalculatedmean of selected fixes’) was used to calculatethe 95% and 80% MCPs. By this method, thearithmetical mean of all fixes is calculated,the point farthest away determined anddeleted, and the arithmetical mean of all fixesrecalculated. This procedure is repeated untilonly 95% or 80% of the fixes remain. Winterhome ranges are calculated in surface areaand presented here over a background of theglobal tree cover derived from remotesensing. Climate data from a large number ofmeteorological stations along the migrationroutes was obtained from the internet.

ResultsThe satellite transmitter fitted to the Hobby,the smallest and lightest unit available at thetime, delivered astoundingly high numbers ofgood Argos Doppler fixes. The completedataset comprised over 2,000 positions, ofwhich 49% were high-quality locations (LC1–3). There were fewer fixes in Europe (onaverage 65 per month) than in Africa (80 per

month), the lowest number being recorded inthe Mediterranean region, which is explainedby interference in this area (Gros & Malardé2006). The percentage of high-quality fixes inEurope (22%) was much lower than that inAfrica (72%). Signal transmission lasted for21.5 months.Altogether, two spring and two autumn

migrations, as well as two wintering periods,were recorded (fig. 1). In 2009 the bird spent49.3% of the year in the wintering area, 7.2%on spring migration, 32.3% in the breedingarea and 11.2% on autumn migration (fig. 2).

Behaviour at the breeding sitebefore departure on migrationAfter being fitted with the transmitter, thefemale behaved completely normally; it keptto its favoured lookout tree and remainedclose to the young birds. On 28th August2008 the bird was located in the vicinity of itsnest for the last time and on 30th August a fixwas made in southern Germany, nearMunich. The male parent remained in the

breeding area and fed the younguntil 18th September. On 22ndSeptember the male and theyoung had also departed onmigration.

Behaviour on migrationAll migration routes were clearlywest of a direct line between thebreeding site and the winteringarea. The fixes recorded farthestfrom this line on migration (andthe respective distances from it)were as follows: 10°30’N 4°40’Eduring the 2008 autumn migra-tion in Nigeria (1,100 km);14°20’N 10°5’E during the 2009autumn migration, also in Nigeria(510 km); 29°30’N 1°33’E duringthe 2009 spring migration inAlgeria (1,230 km); and 18°15’N8°55’W during the 2010 springmigration in Mauritania (2,500km).The spring migration route in

2010 passed over the Strait ofGibraltar but all other migrationroutes crossed the centralMediterranean. North of the

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British Birds 104 • January 2011 • 2–15

1. The female Hobby Falco subbuteo tracked in this paper,shown here after being fitted with the satellite tag at the nest-site, northwest of Berlin, in August 2008.

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border between Nigeria and Cameroon (7°N12°E), the four routes traced were fairly wideapart but were quite similar between 7°N andthe wintering area (fig. 1). In Africa, thespring 2010 route was noticeably farther westthan the other routes, being up to 2,150 kmwest of the autumn 2009 route and up to1,500 km west of the spring 2009 route. Thisresulted in a ‘migration loop’ for 2009/10,which was not the case in 2008/09 (fig. 1). The autumn migration in 2008 (8,525

km) took 49 days, that in 2009 (7,793 km)took 42 days. Spring migration in 2009(7,640 km) took 35 days, while the muchlonger spring 2010 route (8,678 km as far asthe German border) took 38 days. In spring2010 the bird’s migration speed slowed dra-matically in southern Germany and no fixeswere received after this time.

Autumn migration 2008After departure on 28th/29th August, theroute initially took a SSW direction and, aftera short rest from 6th–13th September on theisland of Elba, off the west coast ofItaly, continued in a SSE directionas far as North Africa. From Libya(20th September, 29°50’N13°38’E) migration resumed againin a SSW direction, reaching itsmost westerly point (10°30’N4°40’E) on 30th September inwestern Nigeria, near the borderwith Benin. After an initial 90°switch in direction to the south-east, from 8th October on theNigeria–Cameroon border (7°N12°E) the falcon took an almostsoutherly course. It held thiscourse until arrival at its mainwintering area in southern Angolaon 17th October, after a total flightof some 8,525 km.

Spring migration 2009 Spring migration began some 27km southeast of Quibala (10°50’S15°11’E) and covered a distance of259 km on that day. From north -ern Nigeria it flew progressivelywest of its route the previousautumn, covering daily flight dis-tances of up to 380 km in the rain-

forest region and 395 km over the Sahara. Atthe beginning of May, after some 35 days ofmigration, the bird reached its breeding site(where a male had been observed during thelast few days of April). In total, 7,640 kmwere covered at an average of 218 km/day.Some 5,169 km in 21 days (246 km/day) werecovered as far as Algeria. During the Saharacrossing, 1,184 km were covered in just threedays towards the end of April.

Autumn migration 2009Departure from the breeding area took placeon 29th or 30th August, the bird initiallyheading almost due south. After resting onthe Mediterranean coast in the vicinity of theTunisia–Algeria border from at least 7th to14th September, no other rest stop wasrecorded. The bird’s speed was quickest whencrossing the Sahara and the equatorial rain-forest, with 850 km being covered in Niger on21st–22nd September and 913 km on 26th–27th September in the rainforest region. Incontrast, daily flight distances of only 70–220



2. The breeding site of the Hobby Falco subbuteo discussed in this paper, northwest of Berlin, August 2008.

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km were made in Nigeria andAngola. Around midday on 9thOctober, having covered a total ofat least 7,795 km, it arrived in itswintering area in central Angola(13°41’S 15°52’E).

Spring migration 2010Spring migration began on 31stMarch at 10°37’S 15°8’E. The birdrested in northern Angola on2nd–4th April, before crossing therainforest region on the equatorwhere it made daily flight dis-tances of up to 380 km. On 15thApril the bird changed directionsharply to the northwest on theCameroon–Nigeria border (7°N12°E). It then flew in almost astraight line for 2,280 km towestern Mali, including a stretchof 334 km along the River Nigeron 22nd April. From Mali the birdheaded almost directly north andreached the southern fringe of theSahara on the evening of 24thApril. It reached the Strait ofGibraltar on 30th April and madea night crossing. In Mali andMorocco it migrated 1,243 km on28th–29th April; this averagespeed of 621 km/day is the fastestby this falcon on all the recordedmigration routes. It also movedquickly from Gibraltar to thesouth of France, covering 1,032km on 30th April and 1st May. In contrast, the bird migrated

very slowly from southern France(at an average of just 111 km/day)and did not reach the German–Swiss border at Schaffhausen untilthe evening of 7th May. Up to thispoint it had covered 8,678 km in38 days (228 km/day). Some 9.5days later the Hobby was locatedin southern Germany for the lasttime, in the vicinity of Nurem-berg. It had flown just 191 kmfurther and the distance to thenest-site was still 470 km. Itremains unknown whether or notthe female did reach the breeding

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Fig. 1. The autumn and spring migration routes of an adultHobby Falco subbuteo between its breeding site in Germanyand the wintering area in Angola, from autumn 2008 to spring 2010.

Fig. 2. The annual cycle of an adult Hobby Falco subbuteo asrevealed by satellite telemetry. In 2009 the bird spent 49.3%of the year in the wintering area (blue), 7.2% on springmigration (green), 32.3% of the time in the breeding area(yellow) and 11.2% on autumn migration (red).

area but then chose another site (which iscertainly possible since no male occupied theoriginal nest-site northwest of Berlin in2010).

Migration speedThe transmitter was programmed so that itwas generally possible to record the migra-tion distance for a total of two or more con-secutive days only. However, on ten occasionson spring migration the flight performanceon a single day was recorded. The minimumdaily flight distance was 95 km, themaximum 481 km and the average 248km/day. However, the values of two or moredays taken together indicate that on somedays the falcon flew considerably further than481 km, and must have covered at least 620km. On days with short flight distances thebird presumably adopted a fly-and-foragemigration strategy, especially between thesouthern fringe of the Sahara and thenorthern edge of the rainforest. This was alsothe case south of the rainforest, where thebird covered only about half the daily dis-tance flown over the key barriers of theSahara and the rainforest. On 7th October2008 in Cameroon, for example, the bird hadcovered only 40 km by midday, and from

then until evening it flew only a further 87km.

Crossing the SaharaCrossing the Sahara took some 4–4.5 days oneach occasion. In spring 2009, the birdcrossed some 2,100 km of the Sahara in Nigerand Algeria between the morning of 22ndApril and midday on 26th. On 23rd–25thApril the average daily distance covered inAlgeria was 400 km. In spring 2010, theSahara was crossed during 25th–29th April,mainly in Mauritania (and to a lesser extentin Mali and Morocco), a total distance of1,670 km. On five days the bird covered anaverage distance of 440 km, including thedesert fringes. The exact daily flight distancewas recorded on three days – 25th April (481km), 26th April (212 km), and 27th April(326 km) – followed by the remaining 1,240km on 28th–29th. At 08.18 hrs on 25th, thebird had already flown 123 km from its nightroost, while between 10.00 and 11.00 hrs itflew only a few kilometres. On 27th, the birdstarted migrating as early as 04.00 hrs (sometwo hours before sunrise) but rested from atleast 06.30 to 11.00 hrs. In three cases, averageflight speeds of 25, 30 and 42.5 kph overseveral hours of flight were calculated.



Fig. 3. The marked convergence of the migration routes against the background of the global treecover (derived from remote sensing) during the crossing of the West African evergreen rainforest.The use of the narrowest part of the forest north of Kinshasa is clearly distinguishable.

Kinshasa

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Table 1. Habitat use in the wintering area calculated on the basis of identified night roosts, andtaking account of the excursion into Zambia 2008/09.

No. of night % No. of night %roosts 2008/09 roosts 2009/10

Angolan Miombo woodlands 38 50 45 58

Zambezian Baikiaea woodlands 28 37 19 24

Southern Miombo woodlands 3 4 - -

Kalahari Acacia-Baikiaea woodlands 3 4 12 15

Angolan montane forest-grassland mosaic 1 1 1 1

Angolan Mompane woodlands 1 1 1 1

Western Zambezian grasslands 1 1 - -

Southern African bushveld 1 1 - -

Migration across the rainforestThe West African equatorial rainforestappears to be a significant ecological barrier.All four routes across the rainforest (fromapprox. 5°45’N 12°33’E to 0°15’S 14°20’E)were very close to one another, and from theNigeria–Cameroon border to Angola therewas hardly any deviation. The routes passedthrough a large, roughly north–south cor-ridor (or ‘peninsula’) of more open habitatsdominated by farmland, degraded woodlandand moist savannah (fig. 3). This corridor issome 370 km long and 200 km wide andstretches north from Kinshasa, DR Congo, toabout 0°15’S 14°20’E. This significantlyshortens the distance to be flown over con-tinuous rainforest, to some 450–600 km. In autumn 2008, the lowland forest in

Congo was crossed in a 680-km-long stretch.Here the falcon travelled at a rate of about580 km/day, one of the highest daily dis-tances recorded. In autumn 2009 the distanceflown over the rainforest was c. 695 km,covered at a rate of about 450 km/day. Inspring 2009, a stretch of 730 km was flownover the rainforest between the afternoon of12th April and c. 01.00 hrs on 15th April atan average of 380 km/day. In spring 2010,daily distance covered over the rainforest andadjacent areas was c. 400 km.

Migration during twilight and at nightMigration at night was recorded repeatedlywhile crossing the Sahara and rainforestareas, but also in the Mediterranean. Forexample, in order to reach the northernperimeter of the rainforest in Cameroon, the

bird flew an additional 260 km after sunseton 14th April 2009, and arrived at its nightroost, clear of the rainforest, after midnight.On one part of the route, 57 km in length, itflew at an average speed of 34 km/h. Inspring 2010 the Hobby also covered part ofthe route in darkness until reaching thenorthern fringe of the rainforest. During theearly morning of 9th April, before sunrise, itcovered over 250 km; thereafter, untilmidday, it flew only 90 km. The fixes did notpermit us to establish whether it migratedthroughout the night.The bird migrated in the dark in at least

the early morning hours while crossing theSahara in 2010 (see above). Furthermore, on30th April 2010, the Hobby was located overthe Mediterranean near Gibraltar at 02.54hrs, some 2.5 hours before sunrise. From itssurmised night roost in Morocco it had atthis time already covered 122 km and somust have been on the move for at least threehours.

WinteringOn both occasions, the Hobby winteredmainly in the same regions (Cunene, Huilaand Cuando Cubango) of south and centralAngola and, to a lesser extent, in the farnortheast of Namibia, where it visited thesame areas in both winter periods. The ‘homerange’ in winter was very large with theactual size dependent on the method of cal-culation. In 2008/09 it comprised 406,000km² and in 2009/10 it covered 461,000 km²(Kernel 80%). Calculations based on theMCP method arrived at the following values.In 2008/09, MCP 95% equalled 280,000 km²

and MCP 80% was 226,000 km². In2009/2010, MCP 95% equalled278,000 km² and MCP 80% was248,000 km². An excursion to Zim-babwe in 2008/09 (see below) was notincluded in these calculations.The bird spent about half its time

in winter (50% in 2008/09, 58% in2009/10) in the Angolan Miombowoodlands (fig. 4 and table 1), ahabitat made up of alternating moist,large-leaved savannah and woods5–10 m high interspersed with grass-land, at an altitude mainly 1,000–1,500 m above sea level. The Miombois characterised by several unique eco-logical factors, including an abun-dance of termites, which are animportant food source for the Hobby.The second most important habitatwas the Zambezian Baikiaea woodlands.

Winter 2008/09From 17th October to 7th April therewere 543 fixes in the wintering area, ofwhich 392 were in the classes LC 1–3(fig. 5). Over two months afterarriving in southern Angola it movedfurther in a southeasterly directionand arrived in Zimbabwe on 29thDecember. On 1st January 2009 itreached the southernmost point ofthis winter movement (19°45’S29°45’E), between the cities of Bul-awayo and Harare in central Zim-babwe (fig. 6). The distance migratedfrom the breeding site, not includingregional movement in Angola, was10,065 km up to this point. TheHobby did not linger in Zimbabweand retreated almost immediately toits wintering area in Angola/Namibia.The total distance of this excursionfrom 25th December 2008 to 12thJanuary 2009 was some 2,785 km, atan average of 174 km/day. A total of76 night roosts were identified, ofwhich 66 (87%) were in Angola, threeeach in Namibia, Zimbabwe andZambia, and one in Botswana.In its main wintering area the

Hobby showed a propensity for travel,illustrated by the recording of no



Fig. 4. Roost-site locations during both winteringperiods (2008/09 red, 2009/10 blue) in different habitats(A = Angolan Miombo woodlands, B = Zambezian Baikiaeawoodlands, C = Kalahari Acacia-Baikiaea woodlands, D = Angolan montane forest-grassland mosaic).

Fig. 5. The Kernel home range in winter 2008/09 basedon 69 night roosts in Angola and Namibia (plotted againstthe background of the global tree cover, derived fromremote sensing).

fewer than 543 different tracking fixes. From16th October 2008 to 7th April 2009, the birdnever spent as long as a week in the sameplace and covered a total distance of at least9,025 km. This calculation is based on thedistance between the 76 precise night-roostfixes, which amounted to somewhat less thanhalf of all overnight stops. Within Angola,these fixes, usually recorded at an interval of48 hours, were sometimes more than 300 km

apart. This means that the actual distancecovered by the bird during this winter periodwas significantly greater.

Winter 2009/10The Hobby remained in the same winteringarea from 9th October 2009 to 31st March2010 without any long-distance excursion inthis winter (fig. 7). Some 77 night roosts werelocated, 11 in northwest Namibia (1st–25th

January) and theremainder in Angola.The consecutive dis-tances from roost toroost totalled 6,432 km(fig. 8); as in the pre-vious winter, the realdistance coveredduring winter musthave been considerablygreater. The same areaswere visited repeatedly,some of them thesame as in the pre-vious winter period.

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3. Hobby Falco subbuteo, Tammisaari, Finland, July 2005.

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Fig. 6. The 2,785 km-long excursion to Zimbabwe during winter 2008/09.

Discussion With the advance of satellite-telemetry technology, informationon the ecology and life history ofraptors has been greatly increasedcompared with what could pos-sibly have been gathered duringdecades of conventional telemetryand ringing. However, when usingtelemetry as a study method, theweight of the transmitter (and itsharness) should not exceed 3% ofthe body mass of the studysubject, in order not to affect thebird’s behaviour and thus bias thestudy results (Meyburg & Fuller2007). This limitation has notbeen respected in several recentfalcon studies. The 3% rule stillexcludes 85% of all bird speciesfrom satellite telemetry studiesand, of nearly 10,000 species ofbirds alive today, only about 1,500are large enough to carry even thesmallest, 5-g transmitters. Theprototype of what is currently thesmallest transmitter, weighing just5 g, was first used successfully byus on the adult female Hobbydescribed in this paper.

Early departure of thefemale on migrationIn both years the female departedat the same time (28th/29thAugust), irrespective of whether ornot there were young to be caredfor. This early departure from thebreeding territory of the femaleHobby, long suspected to be thecase with females (Fiuczynski1987), was confirmed in thisstudy. In the first few weeks afterthe young fledge, the female playsan important role in territorialdefence and in the receipt and dis-tribution of prey (chiefly birds)brought back by the male. As theflight skills of the young improve,they reach the returning malebefore the female, so that sheincreasingly takes a lesser role inrearing the young (Fiuczynski



Fig. 7. The Kernel home range in winter 2009/10, based on77 night roosts (plotted against the background of the globaltree cover, derived from remote sensing).

Fig. 8. Changes in location between the 77 night roostsduring winter 2009/10.

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1987). The provision of small birds as foodfor the young is clearly an important precon-dition for the long-distance migration flightthat begins in September, and this, as well asterritorial defence, is reliably carried out bythe male as the young improve their flyingskills.

Migration routesFor most long-distance migrants, ring-recov-eries from Africa are far too few to properlyexplain the patterns and strategies associatedwith migration. We are aware of just twosuch ring-recoveries for the Hobby south ofthe Sahara. A Dutch bird, ringed as nestlingon the Wadden Sea Island of Texel on 26thJuly 1982 (53°03’N 4°43’E), was found deadon 26th November 1992 near Kabwe, Zambia(14°26’S 28°27’E), a recovery distance of7,820 km (Dowsett et al. 2008); while anestling ringed in Pälkäne, southern Finland,on 19th July 2006 was found electrocuted on7th March 2007 in South Africa, a recoverydistance of 9,650 km (Finnish RingingCentre, www.luomus.fi/english/zoology/ringing/index.htm). In addition, Strandberg etal. (2009a,b) published results obtained from

the satellite tracking of four Hobbies betweentheir breeding grounds in Sweden and theirwintering areas in southern Africa (althoughthey were not able to follow the birds inwinter or on their subsequent spring migra-tion).Our satellite-tracked Hobby showed no

clear preference for the shortest sea crossingwhen traversing the Mediterranean. Frequentsea crossings by the smaller falcons have beenreported by earlier radar studies at the southcoast of Spain, in both spring and autumn(Meyer et al. 2000, 2003).The four flight paths plotted were far

apart across much of Africa, the maximumeast–west separation being 2,150 km, a dis-tance that far exceeds the expected normalrange of vision. This suggests that the Hobbydid not navigate by following familiar land-marks but that it could find its target regionsafter extensive deviation, presumably by‘map-based’ navigation and possibly in com-bination with path integration. The fourroutes showed several distinctly non-randomfeatures, however. In particular, there was anoverall westerly bias to the routes, comparedwith a direct line between the breeding and

4. Hobby Falco subbuteo, Tammisaari, Finland, July 2005.

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wintering areas. The westerly deviation froma straight-line route was particularly pro-nounced over and to the north of Nigeriaduring spring migration, especially in 2010.Furthermore, there was a striking conver-gence of the four routes over an inland areaclose to the equator, well north of the bird’sfinal winter destination in Angola, whichclosely matches the findings of Strandberg etal. (2009b). Such convergence of migrationroutes is generally thought to occur inresponse to distinctive topography (forexample the bottlenecks of large soaringbirds at places such as Gibraltar and theBosporus) and/or reflect a species’ navigationto a particular target area, such as a well-defined winter range.The most challenging aspects of our find-

ings to explain are the extensive migrationloop, in particular the extreme westerlycourse, of the spring 2010 migration route;the convergence near the equator; and thevast distances that the bird covered in itswintering area. In particular, we have no con-vincing explanation for the 2010 springmigration route, especially given that mostspecies usually migrate more to the east inspring than in autumn (Newton 2008).Analysis of the data on wind direction andprecipitation from all meteorological stationsalong the migration routes provided us withno further clues, although Strandberg et al.(2009b) suggested that the westward shift ofroutes they observed over the Sahara was inresponse to drift in easterly crosswinds. Inter-estingly, two adult Eleonora’s Falcons F.eleonorae also migrated much farther to thewest in spring than in autumn (Gschweng etal. 2008). One contributory factor to thebird’s route could be the migration tracks ofBarn Swallows Hirundo rustica, HouseMartins Delichon urbicum, Common SwiftsApus apus and other important prey species(hirundines and swifts make up 55% of theavian prey species of the Hobby aroundBerlin; Fiuczynski et al. 2009). Barn Swallowsin particular have similar migration routesand wintering areas to the Hobby, and depar-ture and arrival times in Europe are also verysimilar to those of the Hobby (e.g. Sparks &Braslavská 2001). In France in recent years(2008–10), there has been a close similarityin terms of the passage periods in both

spring and autumn of these two species (seewww.hirondelle.oiseaux.net/migration.html),but the exact migration routes of hirundinesand swifts within Africa are unknown. Inspring, experienced Barn Swallows may beable to return north in about five weeks at aspeed of about 300 km/day (Mead 1970); thisagain is similar to the performance of theHobby, which may exploit the swallows as aconvenient prey species. This is also sup-ported by observations in Zambia (seebelow).The convergence of the Hobby’s routes

near the equator fit neatly with the hypoth-esis that the bird aimed to take advantage ofthe narrowest crossing of the equatorial rain-forest, and this suggests that this habitat isavoided by northern migrants not only forwintering but also during migration. Therainforest may be a barrier not only becausethe habitat structure of the forest isunfavourable for hunting, but also because ofthe weather conditions, with high rainfall.Our results thus support Strandberg et al.(2009b) that the continuous evergreen rain-forest constitutes an important barrier thataffects the major flyways and stopover strat -egies by which Hobbies, and perhaps othermigratory landbirds, travel to and from theirwinter quarters in southern Africa. It is mostimportant that we understand the role of therainforest as an ecological barrier of possiblycontinental-scale significance for the evolu-tion and future of the Palearctic–African birdmigration systems.

Migration speedThe flight speed of the Hobby tracked in ourstudy during outward migration was signifi-cantly faster (8,525 km in 49 days or 7,793km in 42 days, 174 and 185 km/day respec-tively) than the somewhat longer migrationsof the Swedish Hobbies tracked by Strand-berg et al. (2009a), which needed on average61 days for a mean distance of 9,223 km (151km/day). To date there are no other data forus to compare with the spring migrationroutes described here. The differences that wefound in migration speed during the Saharaand rainforest crossings, compared withother parts of the route, were also recordedfor the Swedish Hobbies. The daily rainsassociated with the rainforest may limit the



foraging possibilities for this species and thismay be one explanation of the increasedspeed over and close to the forest.In terms of other species, North American

Peregrine Falcons F. peregrinus flew at similarspeeds in autumn (172 km/day) over a routeof similar length (8,624 km on average)(Fuller et al. 1998). Two Eleonora’s Falconsalso covered somewhat similar daily distances(192 and 219 km) (López-López et al. 2009).The night flight of the Hobby is surprising,however, as this has so far been establishedfor very few species of raptor (Bildstein2006).

WinteringIn Zambia, the first Hobbies to arrive fromthe north often appear in early October(mean date 15th October over 30 years),while departure is in mid March (mean lastdate is 30th March for a 28-year sample);extreme dates are 22nd September and 23rdApril (Dowsett et al. 2008). The main passagesouth seems to be influenced by the arrival ofheavy rains, when the largest numbers of thisspecies are associated with flocks of BarnSwallows.The long distances covered by this indi-

vidual Hobby in the wintering area are sur-prising, as are the vast home ranges. The totaldistance travelled in winter was probablymore than that travelled in autumn or springon migration, at least in winter 2008/09. Itwas not possible to establish the cause ofthese extensive flights. A great deal of thefalcon’s diet probably consisted of energy-rich termites, which are particularly commonin the rainy season in the areas of Angolavisited by the bird. We are not aware of com-parative data for other falcons. However, aBlack Kite Milvus migrans tracked by GPStransmitter covered at least 14,000 km in itswintering area in West Africa (Meyburg &Meyburg 2009). That bird had three differenthome ranges of up to 88,000 km² in consecu-tive years.

Acknowledgments

Our thanks go the responsible authorities forpermission to trap the falcon and deploy thetransmitters. Rouven Polep and Holm Benning enabledus to test transmitter fastenings for long periods onHobbies in captivity. Paul Sömmer ran checks on thebreeding site and erected an artificial nest platform.

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Prof. Dr Bernd-Ulrich Meyburg, Wangenheimstr. 32, 14193 Berlin, Germany; e-mail [email protected]

Dr Paul W. Howey, Microwave Telemetry, Inc., 8835 Columbia 100 Parkway, Suites K & L,Columbia, MD 21045, USA; e-mail [email protected]

Christiane Meyburg, 31, Avenue du maine, 75015 Paris, France; e-mail [email protected] Klaus Dietrich Fiuczynski, Westfalenring 26, 12207 Berlin, Germany; e-mail [email protected]

Bernd-Ulrich Meyburg is chairman of the World Working Group on Birds of Prey (WWGBP). He has carriedout research on no fewer than 16 raptor species since 1992 using satellite telemetry. Paul Howey is presidentand owner of Microwave Telemetry, Inc. (USA), and a pioneer in producing satellite-tracking devices for birds.He built the first 5 g satellite transmitters. Christiane Meyburg worked as a researcher at the NationalInstitute of Statistics and Economic Studies (INSEE) in Paris. Since 1992 she has helped her husband analysethe satellite-tracking data from his projects. Klaus Dietrich Fiuczynski worked as a teacher, completed a PhDon the Hobby and has written a major monograph on this species (a new edition of which is almostcomplete).

Documents

Two complete migration cycles of an adult Hobby tracked by