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

To investigate time, energy, and temperature constraints on hatching asynch rony in Eurasian Kestrels (Falco tinnunculus), we observed females during t he laying period and quantified the time spent hunting to see whether this might limit time spent incubating. We predicted that females would hunt mor e in years when the density of voles was low in spring. Although females sp ent more time outside the nest box in poor-food years, there was only a wea k trend for increased hunting. Only 22 of 68 (32%) of females either perch- or flight-hunted and they caught four prey in 389 hours of observation. Th ere was no relationship between the tendency of females to hunt and the del ivery rate of their mate. Time outside the box was not correlated with ambi ent temperature and the proportion of time hunting was not correlated with prey abundance on the territory. Females did not seem to increase their ene rgy intake by being outside the box, but may still conserve energy by delay ing incubation. We conclude that there are not time or temperature constrai nts on incubation, but we can not rule out energy constraints. It is also p ossible that delaying incubation when food is scarce is adaptive for kestre ls.