Timing of migration and residence areas during the non-breeding period of barn swallows Hirundo rustica in relation to sex and population

We investigated sex- and year-dependent variation in the temporal and spatial movement pattern of barn swallows Hirundo rustica during the non-breeding period. Hundred and three individuals equipped with miniaturized light-level geolocators at three different breeding areas in southern Switzerland and northern Italy provided data for the analysis. We identified a region 1000 km in radius centred in Cameroon as the main non-breeding residence area of these three geographical populations. Five residence areas of males only were in southern Africa, south of 19°S. Most individuals occupied a single site during their stay south of the Sahara. The timing of migration broadly overlapped between sexes and all geographical breeding populations. Between the two study years there was a distinct difference of 5 to 10 d in departure dates from and arrival at the breeding sites. Remarkably, the period of residence in sub-Saharan Africa was very similar (157 d) in the two study years, but their positions in the first year (2010-2011) were about 400 km more to the north than in the second (2011-2012). Independent of the year, individuals with sub-Saharan residence areas further north and east had a shorter pre-breeding migration and arrived earlier than those staying further south and west. In addition, birds breeding in southern Switzerland arrived at their breeding colony 7-10 d later than those breeding only 100 km south, in the Po river plain. Our study provides new information on the variance in migration phenology and the distribution of residence areas in sub-Saharan Africa in relation to sex, population and year. It supports the usefulness of light-level geolocators for the study of annual routines of large samples of small birds.