title: The annual cycle of a trans-equatorial Eurasian-African passerine migrant: different spatio-temporal strategies for autumn and spring migration.
abstract: The small size of the billions of migrating songbirds commuting between temperate breeding sites and the tropics has long prevented the study of the largest part of their annual cycle outside the breeding grounds. Using light-level loggers (geolocators), we recorded the entire annual migratory cycle of the red-backed shrike Lanius collurio, a trans-equatorial Eurasian-African passerine migrant. We tested differences between autumn and spring migration for nine individuals. Duration of migration between breeding and winter sites was significantly longer in autumn (average 96 days) when compared with spring (63 days). This difference was explained by much longer staging periods during autumn (71 days) than spring (9 days). Between staging periods, the birds travelled faster during autumn (356 km d(-1)) than during spring (233 km d(-1)). All birds made a protracted stop (53 days) in Sahelian sub-Sahara on southbound migration. The birds performed a distinct loop migration (22 000 km) where spring distance, including a detour across the Arabian Peninsula, exceeded the autumn distance by 22 per cent. Geographical scatter between routes was particularly narrow in spring, with navigational convergence towards the crossing point from Africa to the Arabian Peninsula. Temporal variation between individuals was relatively constant, while different individuals tended to be consistently early or late at different departure/arrival occasions during the annual cycle. These results demonstrate the existence of fundamentally different spatio-temporal migration strategies used by the birds during autumn and spring migration, and that songbirds may rely on distinct staging areas for completion of their annual cycle, suggesting more sophisticated endogenous control mechanisms than merely clock-and-compass guidance among terrestrial solitary migrants. After a century with metal-ringing, year-round tracking of long-distance migratory songbirds promises further insights into bird migration.
authors: Center for Macroecology, Evolution and Climate, Department of Biology, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark. aptottrup@bio.ku.dk
authors: Anders P
authors: AP
authors: Tøttrup
authors: Raymond H G
authors: RH
authors: Klaassen
authors: Roine
authors: R
authors: Strandberg
authors: Kasper
authors: K
authors: Thorup
authors: Mikkel Willemoes
authors: MW
authors: Kristensen
authors: Peter Søgaard
authors: PS
authors: Jørgensen
authors: James
authors: J
authors: Fox
authors: Vsevolod
authors: V
authors: Afanasyev
authors: Carsten
authors: C
authors: Rahbek
authors: Thomas
authors: T
authors: Alerstam
mesh_terms: D000349:Africa; D025041:Animal Migration; D000818:Animals; D005060:Europe; D005260:Female; D005843:Geography; D008297:Male; D046109:Passeriformes / Q000502:physiology*; D012621:Seasons; D013997:Time Factors