Incubation behavior of Long-tailed Tits: Why do males provision incubatingfemales?

The incubation period of Long-tailed Tits Aegithalos caudatus is highly var iable, ranging from 14 to 21 days. Females alone incubate the eggs, but mal es provide females with some food during the incubation period, although fe males must also forage for themselves. Our aim was to investigate whether m ale provisioning of incubating females influenced female incubation behavio r and the length of the incubation period. Provisioning rates varied betwee n males, and female nest attentiveness was negatively related to short-term variation in the rate at which their partner fed them. However, the provis ioning rate of individual males also varied significantly through time, and there was no significant effect of male care on female incubation across t he whole incubation period. There was no evidence that variation in the beh avior of either males or females influenced the length of the incubation pe riod.