Brood Patches of American Kestrels: An Ecological and Evolutionary Perspective

Abstract

We investigated variation in the number and size of brood patches of female (n = 133) and male (n = 81) American Kestrels Falco sparverius in northcentral Saskatchewan, Canada. We analyzed brood patch size with respect to characteristics of individual birds such as sex, age, size, condition, and clutch volume. All incubating birds developed brood patches but females tended to have larger patches than males. The size of the brood patch was correlated significantly only with the mass of the female. Birds with large eggs or large clutches did not necessarily have large brood patches, and patch size was not associated with laying date or hatching success. In a comparison with other avian taxa, we found kestrels to be unusual in that their three discrete brood patches did not correspond to the modal clutch size of five eggs. Kestrels potentially have difficulty heating all their eggs simultaneously.