Incubation and brooding shift duration in the common murre, uria-aalge

Within- and between-year variation in incubation and chick-brooding shift duration were studied during the 1981–1983 breeding seasons in Common Murre, Uria aalge, pairs on the Gannet Islands, Labrador. Incubation shifts averaged 17 h (range: 1–38 h) and daytime brooding shifts, 4 h (range: 1–14 h). Brooding shifts that included the night, during which change-overs did not occur, averaged 12 h (range: 7–20 h). No differences in shift duration were detected between the sexes but females incubated more at night than did males and were more likely to initiate their incubation shifts in early morning or late evening than males. There was no evidence that pairs tended to change over at the same time each day or that change-overs of neighbouring pairs were synchronized. Shift duration during chick rearing showed significant differences between 1982 and 1983 and the possibility that this was in response to differences in food availability is discussed.