Lizard provisioning and breeding success of kestrels inhabiting an island xeric environment

Abstract

Parental provisioning and breeding success of Eurasian Kestrel (Falco tinnunculus) has been widely studied in some continental populations but not in their island-dwelling counterparts. We studied breeding success of kestrels nesting in natural rocky cavities in southern xerophytic scrub of the oceanic island of Tenerife during eight breeding seasons and its relationships with the endemic Gallot's Lizard (Gallotia galloti). We examined lizard provisioning to assess some hypotheses regarding parental provisioning (e.g. central place foraging, parental investment and territory quality). Kestrels nesting in better quality territories (i.e. better habitats for lizards) advanced laying date and increased clutch and brood size at hatching. This did not result in higher number of fledglings. Lizard biomass provided to the chicks did not decrease with increasing nestling age and was correlated positively with the number of nestlings and chick age. These findings support the hypothesis of parental investment. On considering nestling-rearing period in three 10-day phases, we found significantly lower mean mass of lizards delivered in the first phase than in the other two phases together, with no differences between the last two phases. We suggest that kestrels respond to enhance breeding success and fitness keeping a stable number and quality of fledglings.