The Diet of Eleonora’s Falcons (Falco eleonorae) during the Autumn Migration of Passerine Birds across the Aegean Sea

Diversity Pub Date : 2024-09-02 DOI:10.3390/d16090538
Dietrich Ristow, Michael Wink
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Abstract

Every year, several hundred million birds cross the Mediterranean on their migration from Eurasia to their wintering quarters in Africa. As many migrants travel at night or at high altitudes, direct observations of bird migration are difficult and thus our information about migrating species, numbers and timing is incomplete. An indirect way to assess autumn migration is the analysis of prey remains of Eleonora’s Falcons (Falco eleonorae). These falcons breed in large colonies on islands in the Mediterranean and on the Canary Islands. Many migrants have to pass these islands on their flight to their African wintering quarters. Eleonora’s Falcons appear to be adapted to the autumn bird migration and raise their young between August and October, when migrating birds are abundant. When nestlings have to be fed, falcons exclusively hunt small birds of 10 to 150 g body mass, whereas they prey mostly on aerial invertebrates (Coleoptera, Hymenoptera, Diptera, Orthoptera, Hemiptera, Odonata, Lepidoptera) from November to July. We studied Eleonora’s Falcons from 1965 to 2001 on a rocky islet, north of Crete, which harboured a colony of about 200 breeding pairs. In 1969, 1971, 1977, and 1988 we systematically monitored and collected the pluckings and cached food items in 22 to 36 nest sites each year. Pluckings were systematically analysed later in Germany using a reference collection of bird feathers for identification. In total, we determined more than 111 prey species (mostly Passerines) comprising more than 13,450 individuals. The top 12 prey species were: Willow Warbler (27.8% of all prey items), Red-backed Shrike (10.7%), Spotted Flycatcher (9.9%), Whinchat (8.8%), Common Whitethroat (5.1%), Wood Warbler (3.8), Tree Pipit (2.9%), Icterine Warbler (2.5%), Greater Short-toed Lark (2.5%), Northern Wheatear (1.8%), Common Nightingale (1.6%), and European Pied Flycatcher (1.5%). Eleonora’s Falcons are selective hunters to some degree; thus, the phenology and abundance data derived from the plucking analyses are biased towards slow-flying species or smaller birds (only up to a body mass of 150 g). When the young falcons develop and grow, food demand increases concomitantly. Comparing the total weight of prey over time indicates a correlation with food demand and in consequence with the number of prey items brought to the nest sites by the falcons.
爱琴海秋季候鸟迁徙期间埃莉奥诺拉隼(Falco eleonorae)的饮食情况
每年都有数亿只鸟类穿越地中海,从欧亚大陆迁徙到非洲的越冬地。由于许多迁徙鸟类是在夜间或高海拔地区迁徙,因此很难对鸟类迁徙进行直接观察,因此我们对迁徙鸟类的种类、数量和迁徙时间的了解并不全面。评估秋季迁徙的一个间接方法是分析埃莉奥诺拉隼(Falco eleonorae)的猎物残骸。这些猎鹰在地中海和加那利群岛的岛屿上大量繁殖。许多迁徙者在飞往非洲越冬地的途中都要经过这些岛屿。埃莱奥诺拉隼似乎适应秋季鸟类迁徙,在迁徙鸟类大量出现的 8 月至 10 月间哺育幼鸟。当需要喂养雏鸟时,猎鹰只捕食体重 10 至 150 克的小型鸟类,而在 11 月至 7 月期间,它们主要捕食空中无脊椎动物(鞘翅目、膜翅目、双翅目、直翅目、半翅目、蝶形纲、鳞翅目)。1965 年至 2001 年,我们在克里特岛北部的一个岩石小岛上对埃莱奥诺拉隼进行了研究。1969 年、1971 年、1977 年和 1988 年,我们每年对 22 至 36 个巢穴进行系统监测并收集采摘物和贮藏食物。后来,我们在德国利用鸟类羽毛参考集对采摘物进行了系统分析,以进行鉴定。我们总共确定了超过 111 种猎物(主要是雀形目),数量超过 13 450 只。排名前 12 位的猎物种类是柳莺(占所有猎物的 27.8%)、红背伯劳鵙(10.7%)、斑蝶鴷(9.9%)、白喉莺(8.8%)、普通白喉莺(5.1%)、木莺(3.8)、树啄木鸟(2.9%)、Icterine 莺(2.5%)、大短趾云雀(2.5%)、北杓鹬(1.8%)、普通夜莺(1.6%)和欧洲灰背飞鸟(1.5%)。埃莱奥诺拉隼在某种程度上是选择性捕猎者;因此,拔毛分析得出的物候和数量数据偏向于飞行缓慢的物种或体型较小的鸟类(体重仅达 150 克)。当幼隼发育成长时,对食物的需求也会随之增加。比较一段时间内猎物的总重量表明,猎鹰对食物的需求与猎物被带到巢穴的数量有关。
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