Partial Incubation During the Egg-Laying Period in the BlackcapSylvia atricapilla

Abstract

Partial incubation refers to short bouts of incubation during the egg laying period. I determined the occurrence of partial incubation and its association with the number of eggs in the nest at its onset, in the Blackcap Sylvia atricapilla. Additionally, I studied the relationships between the occurrence of partial incubation at a given number of eggs, air temperature and time of day. At each stage of egg-laying, two nest checks were done each day to establish if the clutch was incubated, until 5 eggs were laid; in this study, a clutch of five was a complete clutch. Incubation of one-, two-, three- and four-egg clutches was observed in 0.0%, 34.2%, 72.2% and 95.8%of the nest checks, respectively. Of the two daily checks, incubation was observed only once in 51.8%, 37.0% and 8.3% of two-, three- and four-egg clutches, respectively, for nests with confirmed incubation. There was no relationship between either air temperature or the time of the nest check and whether or not a clutch was incubated. A significant increase in temperature of the eggs occurred only after the fourth egg was laid.