Delivery of Common Lizards (Zootoca (Lacerta) vivipara) to nests of Eurasian Kestrels (Falco tinnunculus) determined by solar height and ambient temperature

Recent development in video monitoring has allowed collecting of data on prey deliveries at raptor nests, and this offers an opportunity to relate prey selection to short-term changes in environmental factors on a scale of hours. Whereas raptors may specialize on ectothermic prey at southern latitudes, only some generalist raptors may include such prey in their diet at northern latitudes. In particular, at northern latitudes the activity pattern of ectothermic reptiles is strongly dependent on the prevailing weather conditions. To test whether this dependence affects the exposure of reptiles to raptors, we used video recording of prey deliveries at nests of the Eurasian Kestrel ( Falco tinnunculus L., 1758) at 61°N in Norway, where the Common Lizard ( Zootoca ( Lacerta ) vivipara (Jacquin, 1787)) is the only lizard available to kestrels. The probability that a prey item delivered at a kestrel nest was a lizard increased towards midday and also increased independently with increasing ambient temperature, which on average, was 20.2 °C when lizards were delivered compared with 15.7 °C when other types of prey were delivered. Thus, the delivery of lizards by kestrels in our study may be regarded as a functional response, where the abundance of lizards is determined by solar height and ambient temperature.