82 



Birds — Our Living Rcsotincs 



Audubon's 

 Crested 

 Caracara in 

 Florida 



by 



James N. Layne 



Anhbold Biological Station 



A. 



Audubon's crested caracara 

 (Caracara plaiuiis audiibonii) in 

 Florida. 



Lidiibon's crested caracara iCanuani plau- 

 cus aiiduhouii) is a species characteristic of 

 the grassland ecosystems of central Florida and 

 is one of the state's most distinctive birds. The 

 Florida population is threatened and widely 

 separated from the main species' range, which 

 extends from extreme southwestern Louisiana, 

 southern Texas, and southern Arizona to the tip 

 of South America, including Tierra del Fuego 

 and the Falkland Islands. Another isolated pop- 

 ulation occurs on Cuba and the Isle of Pines. 



The number of Florida caracaras is believed 

 to have undergone a substantial decline from the 

 early historic level in the 1950"s and I960"s 

 (Layne in press), with the total state population 

 estimated at 250 in the early I950"s (Sprunt 

 1954) and fewer than 100 birds in the late 

 I960's (Heinzman 1970). Based on the appar- 

 ent continuing decrease in its numbers. 

 Florida's population of Audubon's crested 

 caracara was federally listed as threatened in 

 1987 (Federal Register 1987). As part of a gen- 

 eral study of the life history, ecology, and 

 behavior of the caracara in Florida, I monitored 

 its distribution and population status from 1972 

 to 1991. 



Information was obtained from road and off- 

 road searches in all parts of the known range; 

 systematic roadside and aerial surveys in a 

 5,116-k.m- (1,975-mi-) area within the core 

 portion of the range; published records; muse- 

 um specimens; and sighting reports from over 

 500 cooperators. Logistical limitations prevent- 

 ed surveying the entire potential Florida range 

 thoroughly enough in any given year to obtain a 

 reasonably accurate picture of the distribution 

 and total population. Thus, estimates of the 

 statewide distribution and numbers were based 

 on records combined over 5-year periods: 1972- 

 76, 1977-81, 1982-86. and 1987-91. Searches 

 were most intensive from 1972 to 1981 and in 

 the final period 1987-91. Because areas along 



public roads were surveyed more intensively 

 than those remote from highways, there was a 

 lower probability of detecting caracaras whose 

 territories did not overlap roads than those 

 whose teixitories included roads. This bias 

 appeared to be at least partially compensated for 

 by a tendency of caracaras to concentrate along 

 highways because of the attraction of roadkills 

 as a food source. 



Status and Trends 



The breeding range of Audubon's crested 

 caracara in Florida (Fig. I), based on records 

 from the most recent 5-year period of the study 

 ( 1M87-9I ), did not differ significantly from that 

 during 1973-76 (Layne 1978). Caracaras were 

 documented in 20 counties in central peninsular 

 Florida, with most locations in the same 5- 

 county area as in the earlier years. Counties 

 with 10% or more of the 183 estimated loca- 

 tions during 1987-91 included (number of loca- 

 tions in parentheses) Glades (41), Highlands 

 (34), Okeechobee (23), and Osceola (18). The 

 data indicate no obvious change has occun'ed in 

 the overall range or core area of the distribution 

 of the caracara in Florida from that shown by 

 Howell ( 1932). As there had been relatively lit- 

 tle alteration of the natural habitats of the state 

 up to that time, Howell's range map is assumed 

 to reflect the early historical distribufion. 



The estimated number of adult caracaras 

 during 5-year intervals from 1972 to 1991 

 ranged from 196 to 312 (Fig. 2). The variation 

 between periods reflects differences in sam- 

 pling effort rather than changes in actual num- 

 bers. Thus, the adult population over the 20- 

 year period appears to have been stable with a 

 minimum of about 300 individuals in 150 terri- 

 tories. Further evidence that the population 

 remained generally stable between 1972 and 



Breeding range 

 ■ Core area 



Overall limits 

 - - - Range boundaries 



Ivlain species' range 



Fig. 1. Breeding range of Audubon's crested caracara in 

 Florida based on records from 1987 to 1991: range bound- 

 aries shown by Howell ( 1932), and main species' range in 

 western United States. 



