Reproductive success of American Kestrels: The role of prey abundance and weather

We investigated how natural variation in abundance and availability of the main prey of American Kestrels (Falco sparverius), small mammals, influence d provisioning rates by parents, and offspring size and survival. Provision ing behavior of kestrels was not constrained by the abundance of food in th e environment; however, the availability of food, mediated through variatio n in weather, appeared to significantly influence parental provisioning beh avior. Moreover, variation in weather had clear effects on reproductive suc cess because nestlings exposed to inclement weather were smaller and lighte r at fledging,, and less likely to survive to hedging, compared to nestling s raised during good weather conditions. Prey abundance was not related to offspring size or survival. Our results suggest American Kestrels are limit ed by the availability, as opposed to abundance, of food on territories. It is likely that during our study, prey abundance was above some minimum thr eshold necessary to support successful reproduction, and so variation in we ather affected reproduction more than variation in prey abundance.