Survival, Site Fidelity, and Population Trends of American Kestrels Wintering in Southwestern Florida

The winter population ecology of American Kestrel (Falco sparverius), one of the most abundant and widely distributed raptors in North America, is poorly understood. We systematically searched a 225-km(2) area in Cape Coral, southwestern Florida, for American Kestrels during 14 winters (1 Dec-15 Mar, 1994-2008) to measure their annual apparent survival and to see if individuals returned to the same wintering area. We recaptured 101 of 2,958 banded kestrels during the study. We estimated annual apparent survival of 75% for males and 74% for females using a Cormack-Jolly-Seber model. These estimates are considerably higher than previous estimates for American Kestrels, but are similar to estimates reported for other species of Falco. Forty-six percent of the kestrels estimated to have survived were observed in the study area I year after recapture, based on year-specific color banding. All but six of 101 kestrels were recaptured within 1 km of where they were banded. Four of five kestrels banded as nestlings and subsequently recaptured in the study area were banded in southeastern Pennsylvania, suggesting migratory connectivity. Eighty percent of the kestrels trapped were females, but the proportion of females decreased annually (-3 +/- 1% per year). Overall, the population decreased by an average of 7 +/- 2% per year. Recent land-use change accompanied by increased human density and suburban expansion may be causing the observed trends.