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.

跨撒哈拉迁徙鸟类通常会将年度生命周期的大部分时间用于在萨赫勒（Sahel）地区越冬。野外调查与追踪技术的进步，极大提升了我们对该区域鸟类生态学的研究能力。本研究借助GPS追踪（GPS-tracking）技术，旨在探究鲜为人知的撒哈拉以南非洲地区黄爪隼（Falco naumanni）的非繁殖期移动模式。我们将54只个体共计79条非繁殖期追踪轨迹，划分为三类行为单元：停歇事件（每个非繁殖周期耗时131±25天）、停歇地间的巡游移动（耗时11±10天）以及非定向探索移动（耗时6±5天）。随后，我们分析了整个非繁殖季内，雌雄黄爪隼的巡游移动的时间特征与方向性。无论性别如何，黄爪隼平均会将非繁殖季89%的时间用于在西非的1至4个（平均2个）停歇地停歇。9月末，黄爪隼会以宽泛的战线分布于整个萨赫勒北部区域。但到了12月，它们会聚集至两个独立的集群区域：塞内加尔境内，以及马里-毛里塔尼亚边境沿线。相较于首个及中途停歇地，这些鸟类在这两处后续集群区域的停留时长更长，每日活动强度也更高。在24只被连续追踪多个年度周期的个体中，有20只始终使用塞内加尔或马里-毛里塔尼亚边境的集群区域。剩余4只个体仅在追踪的2至3年后才使用这两处集群区域，或是在不同年度间切换集群。黄爪隼在非繁殖季的东西向巡游移动，以及末期的地理集群倾向，与西非其他食虫猛禽的南向迁徙模式存在显著差异。尽管有31%的西班牙黄爪隼会聚集至已知存在超2万只个体栖息群的塞内加尔，但仍有68%的个体迁至马里-毛里塔尼亚边境区域，该区域仍需开展更多野外基础调查工作。