On the time of alternate incubation by bird

Abstract

Among birds it is generally believed that both the male and the female share the duty of incubation alternately. The reason why they do this is not yet well explained. The author experimented on this problem, and although it is by no means complete, revealed the following fact. Under the natural daylight and darkness the female incubates in a given box between about 4 p. m. and 10 a. m. the following morning, and the male during the remaining daylight hours. When the nest box is curtained and shuts out natural light to a certain extent the changing time becomes late in the morning and becomes early in the afternoon. The male, when the daylight is longer appears to be willing to sit longer.