Female kestrels acquired in Florida in winter as full-grown birds began laying eggs a month later than did those acquired as nestlings from northeastern United States. Egg laying dates of the two groups did not overlap in 1966 through 1968. The later nesting Florida-wintering females may have nested in captivity at a latitude farther south of their normal breeding range than did those from the Northeast. There was an apparent trend of earlier laying in successive years between 1965 and 1968 in our captive birds.....Time intervals between pairing of previously unpaired kestrels and initiation of their first clutches ranged from 8 to 17 days; time intervals between removal of first-clutch eggs and initiation of second clutches for kestrels whose first clutches failed to hatch ranged frosm 11 to 16 days, with the exception of an apparent anomaly of 40 days. Some females laid second clutches prior to fledging of first-clutch young. The egg laying interval averaged 2.4 days, and appeared to be greater between the first two and last two eggs of the clutch than between intervening eggs. Egg sizes differed only slightly between age groups, and no statistical correlation was evident between weights of female kestrels and the size of their eggs.....Although both sexes incubated the eggs, the female assumed a much greater role than the male. Incubation of clutches of five eggs usually began with the laying of the fourth egg. The incubation period (last egg laid to last egg hatched) averaged 27 days. The average interval between hatching of the first and last eggs of clutches containing five eggs was two days.....The average nestling period for the first young hatched in 29 nests was 28.4 days. An exact 1:l secondary sex ratio was recorded in 1967 for complete clutches in which all young fledged.
Additional publication details
Reproductive patterns in captive American kestrels (sparrow hawks)