No apparent gain from continuing migration for more than 3000 kilometres: willow warblers breeding in Denmark winter across the entire northern Savannah as revealed by geolocators

Abstract

BackgroundFor most Afro-Palearctic migrants, particularly small songbirds, spatiotemporal migration schedules and migratory connectivity remain poorly understood. We mapped migration from breeding through winter of one of the smallest Afro-Palearctic migrants, the willow warbler Phylloscopus trochilus, using geolocators (n = 15).ResultsBirds migrated from North European breeding grounds to West Africa via the Iberian Peninsula following a narrow corridor along the West Coast of Africa. Birds then dispersed across the northern Savannah with termination of migration highly variable among individuals. The termination of migration appeared not to be related to timing, current and previous years’ vegetation conditions or biometrics. During winter, most birds moved southwards to improved vegetation.ConclusionThe willow warblers showed a large, unexpected longitudinal spread in winter sites of more than 3000 km between individuals breeding within a 500 m range resulting in a low degree of connectivity. The large wintering area may well be related to generalist behaviour in the species. Our findings contribute to understanding the link between breeding and wintering ecology in long-distance migratory birds.Electronic supplementary materialThe online version of this article (10.1186/s40462-017-0109-x) contains supplementary material, which is available to authorized users.

Weak migratory connectivity, loop migration and multiple non‐breeding site use in British breeding Whinchats Saxicola rubetra

“…Our study presents the first complete description of migration for the species, with a westerly detour of the Sahara in autumn and a direct route across the desert in spring, representing an anticlockwise loop migration. The pattern of migration around the western edge of the Sahara in autumn is also shown by recent tracking studies of several other small long‐distance Afro‐Palaearctic passerines, for example Pied Flycatcher Ficedula hypoleuca (Ouwehand et al 2016) and Willow Warbler Phylloscopus trochilus (Lerche‐Jørgensen et al 2017), and may be a common strategy for Afro‐Palaearctic passerines breeding in western Europe. Despite being greater in distance, this western detour may be less risky energetically, as it avoids the most adverse seasonal Saharan winds (Vansteelant et al 2017).…”

Climatic variation in Africa and Europe has combined effects on timing of spring migration in a long-distance migrant Willow WarblerPhylloscopus trochilus

“…Our choice of the Willow Warbler as a study species was motivated by the availability of detailed information about the timing of its spring migration to northern Europe at a stopover site on the Baltic Sea coast. Different populations of this species migrate to their breeding grounds in Scandinavia and the Baltic region 5,000-12,000 km from their wintering grounds south of the Sahara Desert in west, central, east and southeast Africa (Cramp & Brooks, 1992;Fransson & Hall-Karlsson, 2008;Zwarts et al, 2009;Valkama et al, 2014;Lerche-Jørgensen et al, 2017;Maciąg et al, 2017).…”

Phenotypic and genetic characterization of the East Siberian Willow Warbler (Phylloscopus trochilus yakutensis Ticehurst, 1935) in relation to the European subspecies

“…In contrast to other phenotypic traits, the migratory behaviour separates the European Willow Warbler subspecies relatively clearly, with little variation within populations but with clearly defined contact zones, referred to as migratory divides (Bensch et al 2009). Birds breeding in the range of trochilus migrate to western Africa in autumn, whereas birds from the range of acredula migrate to eastern and southern Africa, supported by ring recoveries (Hedenström and Pettersson 1987), stable isotopes (Bensch et al 2009) and tracking data for trochilus (Lerche-Jørgensen et al 2017). In the Scandinavian contact zone, clines in morphology and migratory behaviours are largely overlapping however east of the Baltic, these are displaced from each other by 1500 km.…”