The onset of incubation in birds: can females control hatching patterns?

We investigated intraspecific variation in incubation behaviour of wild Eurasian kestrels, Falco tinnunculus, in Finland and tested whether patterns of hatching asynchrony could be predicted from patterns of incubation. The timing of the onset of incubation varied considerably for 17 female kestrels. Eggs generally hatched in the order they were laid, and both total hatching span of the clutch and the pattern of eggs hatching on certain days corresponded well with incubation behaviour. This result was consistent with the idea that females have much control over hatching patterns. In the majority (65%) of cases, the proportion of daily incubation increased monotonically with the laying sequence, a pattern described previously in other birds. Unusual patterns of incubation (35%) were most common in females with poor body condition during incubation and may be the result of energy constraints during laying. (C) 1998 The Association for the Study of Animal Behaviour.