Behaviour of female Eurasian Kestrels during laying: are there time constraints on incubation?

To investigate time, energy, and temperature constraints on hatching asynchrony in Eurasian Kestrels (Falco tinnunculus), we observed females during the laying period and quantified the time spent hunting to see whether this might limir time spent incubating. We predicted that females would hunt more in years when the density of voles was low in spring. Although females spent more time outside the nest box in poor-food years, there was only a weak trend for increased hunting. Only 22 of 68 (327o) of females either perch- or flight-hunted and they caught four prey in 389 hours of observation. There was no relationship between the tendency of females to hunt and the delivery rate of their mate. Time outside the box was not correlated with ambient temperature and the proponion of time hunting was not correlated with prey abundance on the territory. Females did not seem to increase their energy intake by being outside the box, but may still conserve energy by delaying incubation. We conclude that there are not time or temperature constraints on incubation, but we can not rule out energy constraints. It is also possible that delaying incubation when food is scarce is adaptive for kestrels.

Wiebe, K. L., Jonsson, K. I., Wiehn, J., Hakkarainen, H. & Korpimaki, E. 2000, Ornis Fennica 77:1-9