Itinerant lifestyle and congregation of lesser kestrels in West Africa

Abstract

Migratory birds often spend a large proportion of their annual cycle in their non-breeding areas. While some species are sedentary after arriving in their non-breeding areas, others engage in itinerary or nomadic movements. Using GPS-tracking we aimed to investigate the little known non-breeding movements of the lesser kestrel Falco namumanni in sub-Saharan Africa. We segment non-breeding tracks (n = 78 tracks by 54 individuals) into staging events (131{+/-} 25 days), itinerant movements between staging sites (11 {+/-} 10 days), and non-directed exploratory movements (6 {+/-} 5 days). We then describe timing and directionality of itinerary movements by male and female kestrels, and explore shifts in habitat use throughout the non-breeding season. Regardless of sex, lesser kestrels spent on average 89% of the non-breeding season at 2-3 staging sites in West Africa. Upon arrival at the end of September, kestrels used disparate sites throughout the Sahel. By December, however, they congregated into two clearly delineated areas in Senegal and along the Malian-Mauritanian border. The birds stayed longer and showed greater daily activity in the latter areas, which were situated closer to wetlands compared to their first and intermediate ones. While 20 of 24 individuals tracked across multiple annual cycles showed consistent staging sites, a few switched between the Senegal and Mauritanian/Malian staging clusters. These results show that rather than tracking suitable climatic conditions southward, lesser kestrels survive the West African dry season by moving into wetland areas within the Sahelian climatic belt. Our findings match reports of lesser kestrel super-roosts in West Africa and stress the conservation value of wetlands along the Senegal River and the Inner Niger Delta in West Africa for the Spanish lesser kestrel population. These areas host 81% of lesser kestrels during 20% of their annual cycle.