REPRODUCTIVE SUCCESS OF AMERICAN KESTRELS NESTING ALONG AN INTERSTATEHIGHWAY IN CENTRAL IOWA

We studied the reproductive success of American Kestrels (Falco sparve rius) nesting in nest boxes attached to the backs of highway signs alo ng Interstate 35 (1-35) in central Iowa, 1988-1992. Nest box occupancy averaged 45.1%. All nest boxes faced either north or south, and there was no significant association between nest box occupancy and nest bo x orientation. European Starlings (Sturnus vulgaris) built nests in al most every nest box not occupied by kestrels. Apparent nesting success , the percentage of nests fledging at least one young, averaged 68.9%. There was no significant association between apparent nesting success and nest box orientation. Using the Mayfield method, we detected a si gnificantly lower probability of survival during the incubation stage than during the brood-rearing stage. Clutch size averaged 4.8 over the five years of the study, and mean hatching success was 62.5%. Mean br ood size was 3.1, and mean number of young in a brood to fledge was 2. 9 (90.9% fledging success). The kestrels in this study had reproductiv e success similar to that of kestrels nesting in nest boxes in other a reas of North America.