1 3 Oecologia (2013) 173:1217–1225 DOI 10.1007/s00442-013-2726-4 BEHAVIORAL ECOLOGY - ORIGINAL RESEARCH Strong migratory connectivity and seasonally shifting isotopic niches in geographically separated populations of a long-distance migrating songbird Steffen Hahn · Valentin Amrhein · Pavel Zehtindijev · Felix Liechti Received: 29 June 2012 / Accepted: 26 June 2013 / Published online: 10 July 2013 © Springer-Verlag Berlin Heidelberg 2013 Irrespective of origin, their isotopic niches were surprisingly similar within a particular period, although sites of residence were distant. However, niche characteristics differed mark- edly between breeding and non-breeding periods, indicat- ing a consistent seasonal isotopic niche shift in the sampled populations. Although nightingales of distinct breeding pop- ulations migrated to different non-breeding areas, they chose similar foraging conditions within specific periods. However, nightingales clearly changed resource use between breeding and non-breeding periods, indicating adaptations to changes in food availability. Keywords Ecological niche · Annual cycle · Non-breeding period · Geolocator · Stable isotopes Introduction The extent to which migratory animals exploit similar habi- tats and resources throughout their annual cycles is impor- tant with regard to population dynamics (Sherry and Hol- mes 1996; Norris and Taylor 2006; Taylor and Norris 2010) as well as other processes such as disease transmission (e.g. Hoye et al. 2011). Until recently, tracking small migrants like songbirds and identifying their areas of residence have been insurmountable challenges (Bridge et al. 2011). The development and application of miniature geoloca- tion data loggers has now partly solved this problem (e.g. Stutchbury et al. 2009; Baechler et al. 2010; Tottrup et al. 2012). Although the use of miniature geolocation data log- gers is becoming more and more widespread, we are still at the beginning of comprehending the complexities of bird migration, especially with regard to larger-scale patterns as inferred from many studied individuals and/or several pop- ulations over longer periods of time. Abstract Whether migratory animals use similar resources during continental-scale movements that characterize their annual cycles is highly relevant to both individual perfor- mances and population dynamics. Direct knowledge of the locations and resources used by migrants during non-breed- ing is generally scarce. Our goal was to estimate migratory connectivity of a small Palaearctic long-distance migrant, the common nightingale Luscinia megarhynchos, and to com- pare resources used in non-breeding areas with resources used at the breeding grounds. We tracked individuals of three geographically separated populations and characterised their stable isotope niches during breeding and non-breeding over 2 years. Individuals spent the non-breeding period in popu- lation-specific clusters from west to central Africa, indicat- ing strong migratory connectivity at the population level. Communicated by Scott McWilliams. Electronic supplementary material The online version of this article (doi:10.1007/s00442-013-2726-4) contains supplementary material, which is available to authorized users. S. Hahn (*) · F. Liechti Department of Bird Migration, Swiss Ornithological Institute, Seerose 1, 6204 Sempach, Switzerland e-mail: Steffen.Hahn@vogelwarte.ch V. Amrhein Zoological Institute, University of Basel, Vesalgasse 1, 4051 Basel, Switzerland V. Amrhein Research Station Petite Camargue Alsacienne, 68300 Saint-Louis, France P. Zehtindijev Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, 2 Gagarin Street, 1113 Sofia, Bulgaria