Doi: https://doi.org/10.13157/arla.72.2.2025.ra5
Authors: José CARRILLO-HIDALGO and Enrique GONZÁLEZ-DÁVILA
E-mail: josechidal@gmail.com
Published: Volume 72.2, July 2025. Pages 241-261.
Language: English
Keywords: birds of prey, Canary Archipelago, dietary niche width, Falco tinnunculus, fitness, foraging strategies, oceanic islands and xeric environments
Summary:
Classical explanations about evolutionary mechanisms regarding island-dwelling birds include expanded trophic niche width and changes in trophic strategies. Although the relationship between trophic niche width and fledging success in raptors is variable, research on this remains scarce for the island-dwelling species. Over seven breeding seasons, we studied intraspecific variation in the trophic niche width and its relation to fledging success of the Eurasian Kestrel Falco tinnunculus canariensis population inhabiting a xeric environment on the oceanic island of Tenerife. Island kestrels behaved as a generalist species with a wide trophic niche due to the large variety of captured insects. Interannual diet width differences were not significant. Dietary overlap between different pairs was high, and unrelated to the distance between them. Trophic diversity showed a significant increase as breeding cycle progressed, i.e. from incubation to chicks older than 15 days old. Fledging success showed a tendency to increase as trophic diversity increased; and was positively correlated with the temperature in May and provision of mammals (especially mice) as well. We found no differences in fledging success between generalist and more specialist pairs, which suggests that both trophic strategies could be quite similar in terms of evolutionary fitness, probably due to both having similar advantages under diverse conditions of prey abundance and availability/predictability. Expanding the trophic niche could ultimately make island-dwelling kestrels less vulnerable to changes in food resource availability, especially under rainfall fluctuations in xeric environments. The generalist trophic strategies of island kestrels may favour a capability for expansion and settlement in new island hábitats.
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