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Breeding Diet of Eurasian Kestrels Falco tinnunculus on the Oceanic Island of Tenerife

The diet of Eurasian Kestrels Falco tinnunculus during the breeding season is well documented in continental populations, but not in their island-dwelling counterparts. The subspecies F. tinnunculus canariensis is a habitat-generalist on the oceanic island of Tenerife, one of its southernmost breeding sites in the Western Palaearctic. We analysed trophic diversity and diet in its main five habitat-types by identifying 5284 prey items in regurgitated pellets from nest sites and roosting sites collected during two consecutive breeding seasons. Secondly, we analysed 2585 prey remains collected from nest sites during 19 breeding seasons. In terms of numbers, insects (mainly Orthoptera and Coleoptera) predominated in pellets: 71% in chicks and 89% in adults, with variation in taxa according to habitat. This reflects opportunistic predation of insects, with grasshoppers being the staple diet in subalpine scrub (above 2000 m a.s.l). The endemic Gallot's Lizard Gallotia galloti provided the greatest biomass in pellets (58% in chicks, 55% in adults) and comprised the most abundant source of prey remains found at nest sites (92% in terms of numbers). Chick diet showed broader trophic diversity than adults. We found high overlap in diet composition between habitats in Tenerife (71% chicks; 66% adults). Kestrels inhabiting anthropogenic environments and northern scrub showed broader trophic diversity; those inhabiting subalpine scrub showed the lowest values. Kestrels inhabiting different habitats in Tenerife showed broad trophic diversity which suggests opportunistic and flexible foraging strategies, as expected of a generalist species. Regardless of habitat, trophic diversity showed high overlap in adult diet composition not only between the Canary Islands (87%), but also between insular and continental reference populations, especially the Iberian Peninsula (81%). Thus, the generalist habits of the Eurasian Kestrel seem to predominate over any expected ecological adaptations associated with island populations.