Negotiating an ecological barrier: crossing the Sahara in relation to winds by common swifts

Åkesson, S., Bianco, G. & Hedenström, A. (2016). Negotiating an ecological barrier: crossing the Sahara in relation to winds by common swifts. Phil. Trans. R. Soc. B 371: 20150393. doi: 10.1098/rstb.2015.0393

Abstract

The Sahara Desert is one of the largest land-based barriers on the Earth, crossed twice each year by billions of birds on migration. Here we investigate how common swifts migrating between breeding sites in Sweden and wintering areas in sub-Saharan Africa perform the desert crossing with respect to route choice, winds, timing and speed of migration by analysing 72 geolocator tracks recording migration. The swifts cross western Sahara on a broad front in autumn, while in spring they seem to use three alternative routes across the Sahara, a western, a central and an eastern route across the Arabian Peninsula, with most birds using the western route. The swifts show slower migration and travel speeds, and make longer detours with more stops in autumn compared with spring. In spring, the stopover period in West Africa coincided with mostly favourable winds, but birds remained in the area, suggesting fuelling. The western route provided more tailwind assistance compared with the central route for our tracked swifts in spring, but not in autumn. The ultimate explanation for the evolution of a preferred western route is presumably a combination of matching rich foraging conditions (swarming insects) and favourable winds enabling fast spring migration.

A Common Swift (Apus apus) equipped with a micro data logger that measures light (Susanne Åkesson / Lund University)

A Common Swift (Apus apus) equipped with a micro data logger that measures light (Susanne Åkesson / Lund University).

Map of stopover areas before initiating migration across the Sahara Desert (triangles), stopover areas on passage (filled yellow circles) and stopover or final wintering areas at arrival after crossing the barrier (squares), for different populations of common swifts breeding in north, central and south Sweden as recorded for spring and autumn by miniature geolocators.

Map of stopover areas before initiating migration across the Sahara Desert (triangles), stopover areas on passage (filled yellow circles) and stopover or final wintering areas at arrival after crossing the barrier (squares), for different populations of common swifts breeding in north, central and south Sweden as recorded for spring and autumn by miniature geolocators. Solid lines are connecting routes for birds recorded outside equinox periods, while dashed lines connect starting and endpoints for swifts passing the Sahara during the equinox period. Lines connecting departure, stopover and arrival events simplify the assumed migratory pathway of the birds (Åkesson et al. 2016 – DOI: 10.1098/rstb.2015.0393)

 

The migration of the Great Snipe (Gallinago media): intriguing variations on a grand theme

Lindström, Å., Alerstam, T., Bahlenberg, P., Ekblom, R., Fox, J. W., Råghall, J., & Klaassen, R. H. G. (2016). The migration of the great snipe Gallinago media: intriguing variations on a grand theme. Journal of Avian Biology 47: 321–334.
Free access (now)

Abstract:

The migration of the great snipe Gallinago media was previously poorly known. Three tracks in 2010 suggested a remarkable migratory behaviour including long and fast overland non-stop flights. Here we present the migration pattern of Swedish male great snipes, based on 19 individuals tracked by light-level geolocators in four different years. About half of the birds made stopover(s) in northern Europe in early autumn. They left the breeding area 15 d earlier than those which flew directly to sub-Sahara, suggesting two distinct autumn migration strategies. The autumn trans-Sahara flights were on average 5500 km long, lasted 64 h, and were flown at ground speeds of 25 m s−1 (90 km h−1). The arrival in the Sahel zone of west Africa coincided with the wet season there, and the birds stayed for on average three weeks. The birds arrived at their wintering grounds around the lower stretches of the Congo River in late September and stayed for seven months. In spring the great snipes made trans-Sahara flights of similar length and speed as in autumn, but the remaining migration through eastern Europe was notably slow. All birds returned to the breeding grounds within one week around mid-May. The annual cycle was characterized by relaxed temporal synchronization between individuals during the autumn–winter period, with maximum variation at the arrival in the wintering area. Synchronization increased in spring, with minimum time variation at arrival in the breeding area. This suggests that arrival date in the breeding area is under strong stabilizing selection, while there is room for more flexibility in autumn and arrival to the wintering area. The details of the fast non-stop flights remain to be elucidated, but the identification of the main stopover and wintering areas is important for future conservation work on this red-listed bird species.

The autumn (a) and spring (b) migration of great snipes travelling between the breeding site in Sweden and their winter quarters in central Africa

The autumn (a) and spring (b) migration of great snipes travelling between the breeding site in Sweden and their winter quarters in central Africa. Green dots show the breeding site according to the light geolocators, orange and yellow dots show stopover sites in Europe/northern Africa and sub-Saharan Africa, respectively, and blue dots the final wintering sites. Red solid lines mark the nonstop flights, and grey thin lines show shorter flights.

From Scotland to Algeria: Geolocators reveal migration and wintering areas of Ring Ouzel (Turdus torquatus)

Sim, I. M. W., Green, M., Rebecca, G. W. & Burgess, M. D. (2015). Geolocators reveal new insights into Ring Ouzel Turdus torquatus migration routes and non-breeding areas. Bird Study 62: 561–565.  doi: 10.1080/00063657.2015.1077779
PDF in ResearchGate.net

Abstract:

The first details of the migration pattern of a male Ring Ouzel Turdus torquatus, fitted with a geolocator on its Scottish breeding grounds, showed that it wintered in the Algerian Atlas Mountains, substantially east of the suspected main wintering area.

Ring Ouzel (Turdus torquatus - Merle à plastron - دج مطوق), Algeria

Ring Ouzel (Turdus torquatus – Merle à plastron – دج مطوق), Algeria, November 2015 (photo: Amine Djabari)

 

From Scotland to Algeria: Ring Ouzel (Turdus torquatus) migration and wintering areas

Median autumn stopover and wintering areas (ellipses) identified from geolocations from an ouzel tracked from Scotland, and recovery locations of British-ringed ouzels. Stopover and winter location ellipses represent the standard deviation of locations around the median point. British-breeding ouzels recovered in autumn (September–November: stars), winter (December–February: open circles) or spring (March–April: upward triangles) are shown alongside non British-breeding ouzels recovered during September–ovember (filled circles). http://dx.doi.org/10.1080/00063657.2015.1077779

Wintering and migration routes for Ortolan Buntings from Sweden determined with geolocators

Selstam, G., Sondell, J. & Olsson, P. (2015). Wintering area and migration routes for Ortolan Buntings Emberiza hortulana from Sweden determined with light-geologgers. Ornis Svecica 25: 3–14.
PDF in ResearchGate.net

Summary:

The decrease of Ortolan Bunting Emberiza hortulana in Western Europe over the last five decades has caused serious concern for the survival of this species in Sweden. In order to find out the migration routes and wintering location, we equipped several males with geologgers. Our data show annual cycles of migrations routes, wintering grounds and time schedules for seven re-trapped birds. The wintering area in West Africa is savannah woodland in a mountainous landscape in Mali and Guinea. The migration routes follow more or less the great circle between the breeding and wintering areas. Most birds were likely to have passed the well-known Ortolan catching area in les Landes south of Bordeaux in France during autumn migration.

During autumn migration, all the birds made stopovers on the Iberian Peninsula or in Morocco, lasting from 6 to 32 days.

The birds started their spring migration in late March or first half of April. All birds arrived a few days later to stopovers in Morocco or Spain, lasting from 5 to 18 days.

Migration routes for Ortolan Buntings (Emberiza hortulana) between Sweden and sub-Saharan Africa

Migration routes for Ortolan Buntings (Emberiza hortulana) between Sweden and sub-Saharan Africa. Longer stays are indicated with numbers (equalling the number of days spent there). Figures given with regular type represent autumn and bold figures represent spring periods. See the article for more details and other 5 birds.

Annual cycle and migration strategies of Great Reed Warbler as revealed by a geolocator study

Lemke HW, Tarka M, Klaassen RHG, Åkesson M, Bensch S, Hasselquist D & Hansson.B. (2013) Annual Cycle and Migration Strategies of a Trans-Saharan Migratory Songbird: A Geolocator Study in the Great Reed Warbler. PLoS ONE 8(10): e79209. doi: 10.1371/journal.pone.0079209

Abstract:

Recent technological advancements now allow us to obtain geographical position data for a wide range of animal movements. Here we used light-level geolocators to study the annual migration cycle in great reed warblers (Acrocephalus arundinaceus), a passerine bird breeding in Eurasia and wintering in sub-Saharan Africa. We were specifically interested in seasonal strategies in routes and schedules of migration. We found that the great reed warblers (all males, no females were included) migrated from the Swedish breeding site in early August. After spending up to three weeks at scattered stopover sites in central to south-eastern Europe, they resumed migration and crossed the Mediterranean Sea and Sahara Desert without lengthy stopovers. They then spread out over a large overwintering area and each bird utilised two (or even three) main wintering sites that were spatially separated by a distinct mid-winter movement. Spring migration initiation date differed widely between individuals (1-27 April). Several males took a more westerly route over the Sahara in spring than in autumn, and in general there were fewer long-distance travels and more frequent shorter stopovers, including one in northern Africa, in spring. The shorter stopovers made spring migration on average faster than autumn migration. There was a strong correlation between the spring departure dates from wintering sites and the arrival dates at the breeding ground. All males had a high migration speed in spring despite large variation in departure dates, indicating a time-minimization strategy to achieve an early arrival at the breeding site; the latter being decisive for high reproductive success in great reed warblers. Our results have important implications for the understanding of long-distance migrants’ ability to predict conditions at distant breeding sites and adapt to rapid environmental change.

Great Reed Warbler Acrocephalus arundinaceus

Great Reed Warbler Acrocephalus arundinaceus (Vitaliy Khustochka on flickr, licence CC-by-nc)

Spatial patterns in North Africa:

The majority of males crossed the Mediterranean Sea and Sahara Desert without stopovers in a flight that exceeded 24 hours in duration, in a geographical window spanning from Tunisia/Algeria in the west to Libya in the east.

In spring, after crossing the Sahara desert, all great reed warbler males stopped just south of the Mediterranean Sea in northeast Algeria and western Tunisia. From the stopover in North Africa most males took off in a north-easterly direction towards Italy and Balkan, which allowed these birds to pass east of the Alps and to return more or less on the same track through Europe as taken in autumn.

A completely unexpected result was that all males spent 1-2 weeks at the end of April or beginning of May in a rather restricted area in north-eastern Algeria and western Tunisia, independent of where along the west–east axis of sub-Saharan Africa they had spent their second part of the winter.

Inferred migration routes, mid-winter movements and stopover sites from geolocator data of male great reed warblers

Inferred migration routes, mid-winter movements and stopover sites from geolocator data of male great reed warblers.
(A) Migration routes and mid-winter movements (blue: autumn; green: spring; yellow: mid-winter).
(B) Stopover sites (stays for more than 36-hours) in autumn (blue) and spring (green), and wintering sites (yellow). Breeding site is indicated (star). Data are for 8 males in autumn and winter, and 6 males in spring. doi:10.1371/journal.pone.0079209.g001

Short‐distance migration of Wrynecks from Central European populations

Wijk, R. E., Schaub, M., Tolkmitt, D., Becker, D. & Hahn, S. 2013. Short-distance migration of Wrynecks Jynx torquilla from Central European populations. Ibis 155 (4): 886–890.  doi: 10.1111/ibi.12083
PDF in ResearchGate.net

Abstract:

European Wrynecks Jynx torquilla torquilla have generally been considered to be long-distance Palaearctic–African migrants that spend the non-breeding season in Sahelian Africa, where they have been reported regularly. Results from tracking individual birds showed that Wrynecks from two Central European populations migrated only relatively short distances to the Iberian Peninsula and northwestern Africa (c. 1500 km and 3000 km, respectively), compared with a minimum distance of about 4500 km to Sahelian Africa. Additionally, differences in wing lengths of populations from Central and Northern Europe support the idea of leap-frog migration, populations from Northern Europe being long-distance migrants with a non-breeding distribution in Sahelian Africa.

Wryneck (Jynx torquilla)

Wryneck Jynx torquilla (Åsa Berndtss on flickr, license: CC-by)

First evidence of a 200-day non-stop flight in a bird

Liechti, F., Witvliet, W., Weber, R., & Bächler, E. (2013). First evidence of a 200-day non-stop flight in a bird. Nature Communications 4:2554. doi: 10.1038/ncomms3554

Abstract:

Being airborne is considered to be energetically more costly as compared with being on the ground or in water. Birds migrating or foraging while airborne are thought to spend some time resting on the ground or water to recover from these energetically demanding activities. However, for several decades ornithologists have claimed that some swifts may stay airborne for almost their whole lifetime. Here we present the first unequivocal evidence that an individual bird of the Alpine swift (Tachymarptis melba) can stay airborne for migration, foraging and roosting over a period of more than 6 months. To date, such long-lasting locomotive activities had been reported only for animals living in the sea. Even for an aerodynamically optimized bird, like the Alpine swift, flying requires a considerable amount of energy for continuous locomotive control. Our data imply that all vital physiological processes, including sleep, can be perpetuated during flight.

Alpine Swift (Tachymarptis melba)

Alpine Swift (Tachymarptis melba) (Ferran Pestaña on flichr, license: CC-by-sa)

Communiqués de presse de la Station ornithologique suisse (08.10.2013) :

Champion du monde en vol d‘endurance

Nouveau record : le martinet à ventre blanc six mois non-stop dans les airs

Maestro avéré du vol non-stop, le martinet à ventre blanc passe la moitié de l’année dans les airs. L’agile volatile doit son titre à une technique des plus modernes, qui a permis aux chercheurs de la Station ornithologique suisse de prouver ce dont on se doutait depuis longtemps.

Sempach – Les oiseaux aussi se voient obligés de poser « patte » à terre de temps en temps pour se nourrir ou tout simplement se reposer. Les martinets font pourtant exception. Parfaitement adaptés à la vie dans les airs, ces acrobates aériens se nourrissent d’insectes volants qu’ils prélèvent au passage. On se doutait bien qu’ils ne se posaient même pas pour dormir : l’observation au radar de martinets noirs tournant très haut dans le ciel nocturne avait déjà mis la puce à l’oreille des ornithologues.

Une performance désormais confirmée par les chercheurs de la Station ornithologique suisse de Sempach, qui ont prouvé que leur cousin le martinet à ventre blanc est capable de voler en continu pendant plus de six mois. En 2011, les chercheurs ont équipé des martinets à ventre blanc de géolocalisateurs après leur nidification. Développées en collaboration avec la Haute école spécialisée bernoise de Burgdorf, ces petites merveilles technologiques d’environ 1 g permettent de mesurer et d’enregistrer la luminosité de l’endroit où se trouve l’oiseau pendant une année. La longueur du jour, et ainsi la position géographique de l’oiseau, sont ensuite calculées à partir de ces données. Spécialité de cette étude, ces appareils étaient munis d’un capteur d’activité enregistrant et différenciant les phases de battement d’ailes de celles de repos.

Ainsi frétés d’un géolocalisateur, les martinets à ventre blancs prirent la direction de leurs quartiers d’hiver. Après y avoir passé la saison froide, ils réintégrèrent leurs sites de nidification suisses, où les ornithologues les délestèrent de leur petit sac à dos. « L’analyse des données de trois martinets a montré que ces oiseaux passent l’hiver surtout en Afrique de l’Ouest», explique Felix Liechti, responsable du département « migration des oiseaux » à la Station ornithologique et premier auteur de l’étude. « Révolutionnaire est la découverte que ces martinets volent en continu pendant leur migration et dans leur zone d’hivernage »

Ces résultats démontrent que les martinets à ventre blanc sont aussi capables de maintenir toutes leurs fonctions corporelles vitales pendant un vol d’endurance. Ils n’ont pas besoin du même type de sommeil que nous autres humains.

Migration routes and non-breeding range of three Alpine swifts breeding in Switzerland

Les martinets à ventre blancs suisses hivernent en Afrique de l’Ouest. Chaque couleur représente un individu différent. Les surfaces colorées indiquent les zones où les oiseaux ont séjourné un certain temps.
(Foto: © Station ornithologique suisse)

Geolocator (Felix Liechti)

Les géolocalisateurs ont été miniaturisés en continue ces dernières années.
(Foto: © Felix Liechti, Station ornithologique suisse)