Reproductive performance of American Kestrels laying replacement clutches

Abstract

Egg dimensions, nestling growth, and reproductive success were compared between first and second clutch nests of American Kestrels (Falco sparverius) to determine the influence of renesting on fledging success. Eggs were removed from 11 nests during 1982–1983. Eight nests served as controls. Most pairs (81.8%) renested on their original territory. We found no significant differences in egg dimensions, fertility, or hatchability between the two groups. Second clutch males (n = 6 clutches) were smaller at hatching than males from first clutches (n = 8 clutches). By day 24 these males (n = 5 clutches) were heavier, with significantly longer manus and antebrachia than first clutch males (n = 3 clutches). However, five of eight first clutch nests fledged all males before day 24. Males remaining in first clutch nests beyond day 24 were lighter with significantly smaller antebrachia by day 18 than males fledging before day 24. This may have biased our comparisons between first and second clutch males. No significant differences in growth were found between female groups. First-clutch progeny fledged significantly younger than second-clutch birds. Males fledged earlier than females in first clutches, but the sexes fledged simultaneously in second clutches.