The Length of Incubation in Relation to Nest Initiation Date and Clutch Size in Dabbling Ducks

Abstract

There are a growing number of studies which suggest that variable incubation periods may be the norm for waterfowl, and that this variation may be correlated with other life-history traits. I examined variation in length of incubation in relation to nest initiation date and clutch size in five species of dabbling ducks during 1995 and 1996. I also conducted a manipulative experiment to directly assess the relationship between clutch size and incubation period in Blue-winged Teal (Anas discors). The length of incubation declined seasonally for all species and in both years. After controlling for nest initiation date, incubation periods were positively correlated with clutch size in only one species during one of two years. Enlarged clutches were incubated two days longer than control or reduced clutches, although reduced and control clutches had similar incubation lengths. These results suggest that clutch size explains only a small amount of the total variation in incubation length, and the cost of incubation may operate with other factors to help limit clutch size in Blue-winged Teal.