Nest attendance during egg laying in pheasants.

As precocial bird species hatch synchronously, incubation during the egg-laying stage should be disadvantageous because it makes the embryos develop asynchronously. We established the patterns of nest attendance during egg laying and the start of incubation in ring-necked pheasants, Phasianus colchicus, and tested three hypotheses regarding the advantage of early incubation. To determine nest attendance, we measured egg temperatures in real pheasant nests. Females spent more time on the nest as laying progressed, with an average of 6.4 h at a clutch size of 10. At the start of incubation, nest attendance increased to over 20 h/day. On the day before full incubation, time spent on the nest was positively correlated with the female's condition and negatively with the number of breeding attempts she had already made that season. The hypothesis that an early start of incubation improves egg viability was rejected, as the predicted relationship between the number of eggs laid after the start of incubation and the number laid before the start of incubation was not significant. We also rejected the possibility that early incubation reduces the risk of nest parasitism, as it was negatively related to the number of females radiotracked around the nest. Our data supported the hypothesis that early incubation reduces the risk of nest predation by shortening the period of exposure, as the number of eggs laid after incubation started was positively related to the number of breeding attempts made by the female, and thus to the perceived predation risk, but was negatively related to the time of season. Copyright 1999 The Association for the Study of Animal Behaviour.