Final Report, Habitat Associations, Reproduction, and Foraging Ecology of Audubon's Crested Caracara in South-central Florida

Humphrey, Stephen; Morrison, Joan

ABSTRACT: The crested caracara (Caracara plancus) is a unique raptor/scavenger with a limited North American distribution. An isolated population occurs in south-central peninsular Florida where the species inhabits open grassland habitats. The status of this population has long been subject of concern. In recent decades, grassland and prairie habitats in this region have undergone extensive conversion to urban and agricultural development. Concomitant with this habitat loss has been the apparent contraction of the caracara's historic range and the population is believed to be in a long-term decline. We studied the reproductive ecology, habitat associations and foraging ecology of crested caracara in south central Florida from August 1993 through June 1996. The purpose of this research was to provide basic ecological information for Florida's caracara population, particularly information that is relevant to management. Our research focused on documenting the dispersion and reproductive success of breeding pairs across the population's range and on assessing relationships between the species' distribution and cattle ranches, where most caracaras now apparently persist. We monitored nesting activity in 65 territories during the 3 years of the study. Florida's caracaras exhibited high territorial occupancy and breeding rates, nesting success, and productivity. Although caracaras may breed from September through June, the breeding cycle is strongly tied to the annual precipitation cycle and the peak of egg laying occurs in January. Pairs can make several nesting attempts per year. Renesting occurred predictably following an early season failure. Pairs that successfully raised two broods in a season may incur higher inclusive fitness. Estimated probability of survival to recruitment was highest for young from first of two broods. Estimates of home range size and local nesting density determined using telemetry were considerably smaller and higher, respectively, than previously published estimates based on observations of unmarked individuals. Home range size for 25 breeding adult crested caracaras ranged from 551 to 2778 ha, and maximum local density found in Highlands County was 1 pair per 555 ha. Caracaras are highly territorial around the nest but apparently tolerate conspecifics in foraging areas, as home ranges overlapped as much as 35%. Caracaras apparently prefer open, structurally simple habitats for nesting and foraging. Differences in management regimes between private and publicly owned lands result in differences in vegetation structure. These differences translate further into differences in occupancy rate and nesting success within caracara territories. Habitat analyses indicated a positive association of caracara home ranges with improved pastures. The size of individual caracara home ranges was strongly inversely related to the proportion of improved pasture. Caracaras are generalist predators that tolerate some human activity as long as the nest site is left intact. They are diet generalists, feeding on live prey as well as carrion and use wetlands for foraging more than originally believed. A conservation strategy for this population should be based on protecting known nest sites and areas where juveniles congregate, and should focus at a regional scale. Management plans must address effects of habitat loss and degradation, particularly conversion of pastures to citrus and sugar cane. Because most suitable habitat is in private ownership, habitat protection must involve cooperative efforts between land management agencies and private landowners.