External factors affecting the duration of broody behavior in the ring dove (Streptopelia risoria).

The object of this study was to investigate factors which determine the duration of sitting in ring doves. This normally lasts ca. 19 days from laying, with very small variation. The period is made up of 15 days incubating eggs and 4-5 days brooding squabs. The duration of sitting is unaffected by substituting fresh or sterile eggs, and can only be slightly influenced by substituting foster squabs or new eggs just before or after hatching. The sitting period appears to be predetermined to run for 19 days following laying. The maintenance of sitting, however, requires the presence of the nest and eggs, and can be drastically varied by keeping subjects in continuous daylight or on a day of 6 hr light:6 hr dark (6 L:6 D). Birds kept on ahemeral cycles (11 L: 10 D; 13 L:14 D) displayed significantly different periods of incubation on infertile eggs and recycling, indicative of an endogenous circadian basis to the timing mechanism.