Itinerant lifestyle and congregation of lesser kestrels in West Africa

Trans-Saharan migrants often spend a large proportion of their annual cycle wintering in the Sahel. Advances in fieldwork and tracking technology have greatly enhanced our ability to study their ecology in these areas. Using GPS-tracking we aimed to investigate the little-known non-breeding movements of the lesser kestrel Falco naumanni in sub-Saharan Africa. We segment non-breeding tracks (n = 79 tracks by 54 individuals) into staging events (131± 25 days per non-breeding cycle), itinerant movements between staging sites (11 ± 10 days), and non-directed exploratory movements (6 ± 5 days). We then describe timing and directionality of itinerant movements by male and female kestrels throughout the non-breeding season. Regardless of sex, lesser kestrels spent on average 89% of the non-breeding season staging at 2 (range = 1–4) sites in West Africa. At the end of September, kestrels arrived along a broad front throughout the northern Sahel. By December, however, they congregated into two distinct clusters in Senegal and along the Malian-Mauritanian border. The birds stayed for longer periods and showed greater daily activity in the latter areas, compared to their first and intermediate ones. Among 24 individuals tracked along multiple annual cycles, 20 individuals consistently used the Senegalese or Malian-Mauritanian cluster. The remaining four birds used these clusters only after 2-3 years of tracking or switched between clusters across years. The eastward and westward itinerant movements of lesser kestrels during the non-breeding season, coupled with their tendency to cluster geographically towards the end, differ from the southward movements of other insectivorous raptors in West Africa. While 31% of Spanish lesser kestrels converged in Senegal, where roosts of > 20,000 birds are known, 68% moved into the Malian-Mauritanian border region where more groundwork is needed.