Breeding Biology and Productivity of Florida's Crested Caracaras

Abstract

I studied the breeding biology of Crested Caracaras (Caracara plancus) in south-central Florida from 1994 through 1996. Reproductive activity was monitored year-round on 30, 48, and 55 territories, respectively. Pairs remained on breeding territories throughout the year and exhibited strong fidelity to the nest site between years; however, annual turnover rate among known breeding individuals was approximately 18%. Territorial occupancy and breeding rates on known occupied territories averaged 95% and 98%, respectively. Observed patterns of breeding activity and nesting success suggested a link between reproduction and precipitation. Active nesis were found from September through June, but most nesting activity corresponded with the dry season. November through April. Egg laying in many pairs occurred following an abrupt decline in precipitation in the fall each year. The overall probability of a nest producing at least one independent young was 72%; however, nest success varied throughout the breeding season, being lowest and most variable for early- and late-season nests. Based on 98 nests with complete records, mean clutch size was 2.23 eggs, 61.2% of nestlings fledged successfully, and 48.4% of all eggs laid resulted in independent young. Clutches of three produced the most independent young per breeding attempt in all years. Annual population productivity was enhanced because pairs made more than one nesting attempt per breeding season, either by renesting following an early season failure or by producing second broods. Clutch size, probability of nest success, probability of renesting, and number of fledglings produced per attempt all declined as the breeding season progressed. Mortality factors included weather, predation, chicks falling out of nests, and vehicle collisions with fledglings. Environmental variability may influence spatial and temporal variation in timing of reproduction and nesting success of Crested Caracaras in Florida.