Audubon's Crested Caracara

Polyborus plancus audubonii

Description

The Audubon's crested caracara is a large raptor with a crest on the top of its head, a naked face, heavy bill, elongated neck, and unusually long legs. Its body length is 20-25 in (50-64 cm) and the wingspan is about 47 in (120 cm). The adult is dark brownish black on the crown, wings, back, and lower abdomen. The lower part of the head, throat, upper abdomen, and under tail coverts are white, sometimes tinged with yellow. The breast and upper back are whitish, heavily barred with black. The tail is white with narrow, dark crossbars and a broad, dark terminal band. Prominent white patches are visible near the tips of the wings in flight. The large white patches in the primaries and the white tail, broadly tipped with black, are both conspicuous in flight and can be recognized at a long distance. Juveniles have a similar color pattern but are brownish and buffy with the breast and upper back streaked instead of barred. Sub-adults resemble adults but are more brownish in color. Adults have yellow orange facial skin and yellow legs. Facial skin of juveniles is pinkish in color, and the legs are gray. The full adult plumage is obtained sometime after age two, and age at first breeding is unknown.

Behavior

The bare skin on the face of this bird is an interesting and distinctive feature. When the bird is at rest, preening or being preened, or engaged in other non-aggressive behaviors, the facial skin is bright orange-red. When threatened, the color of the facial skin changes to a pumpkin color and finally to pale yellow. Apparently, threat or fear causes blood to bypass the subepidermal blood vessels, resulting in a change in facial skin color. The caracara's crest is also used for communication. When a caracara is comfortable and not threatened, the crest lies flat. The crest is raised if it feels threatened, frightened, or is on alert.

The feet and flight behavior are also notable. The feet are clearly those of a raptor; however, the talons are flatter, enabling the caracara to run and walk more easily than other raptors. The flight resembles that of a northern harrier, but caracaras fly faster and more gracefully. Caracaras are strong fliers and may reach speeds of 40 mph (64 kph). They also soar in large circles at great heights.

Caracaras are often seen perched on fence posts, power poles, or other high positions. Since this sub-species is diurnal, the caracara can be easily observed by scientists and the public. Not much information is available on vocalizations; however, in the morning or evening, the caracara may throw its head back until it almost touches its shoulders and emit a high, cackling cry that resembles its Brazilian name. Observations of caracaras in Costa Rica and Mexico indicate that this call may be a part of pair formation or courtship. The only other vocalizations heard in Costa Rica were a one-syllable greeting and an alarm call.

Caracaras are non-migratory, although juvenile birds are nomadic. Adult caracaras may be found in the home range year-round. Occasionally large groups of individuals are encountered, which can be attributed to the carrion-feeding habit.

Caracaras are relatively long-lived birds. One caracara was kept in captivity for at least 30 years. The breeding behavior is relatively unknown. Courtship behavior may involve the pair perching next to each other, almost touching, and uttering a cackling call with their head thrown back. Males may occasionally fight in the air.

Caracaras are some of Florida's first raptors to begin nesting. Egg laying begins in early December and the height of the nesting season is in January and February. Nests with eggs have also been found as late as April; caracaras may nest year-round in Florida.

Caracaras construct a new nest each nesting season, often in the same tree as the previous year. The nest is well concealed, and is most often found in the top of a cabbage palm, although nests have been found in live oaks, cypress, Australian pine, saw palmetto, and black gum. Caracaras usually construct their nests 13-59 ft (4-18 m) above the ground; their nests primarily consist of haphazardly woven vines trampled to form a depression. Both adults participate in nest construction.

Clutch size is two or three eggs, but most often two. Incubation lasts for about 28 days and is shared by both sexes. Ordinarily only one brood is raised in a season. If the eggs are taken, a second or even third set may be laid. The young fledge at about eight weeks of age. Double brooding (two clutches successfully reared in one breeding season) has been documented in the Florida population, particularly for pairs that initiate nesting early in December or January.

Caracaras do not vigorously defend their nest site although they are aggressive toward other adult caracaras intruding near the nest. One female remained on the nest until approached to within 4 ft (1.2 m), when she flew to a stub about 12 ft (3.6 m) away and watched. The male soon joined her and they together uttered rasping, cackling noises with their heads bent back upon their backs.

Another possible artifact of the caracaras' non-migratory habit, is the nesting pair may be seen together year-round in the home range. The pair bond is relatively strong, lasting until one mate dies.

Caracaras are highly opportunistic in their feeding habits, eating carrion and capturing live prey. Their diet includes insects and other invertebrates, fish, snakes, turtles, birds, and mammals. Live prey also include rabbits, skunks, prairie dogs, opossums, rats, mice, squirrels, frogs, lizards, young alligators, crabs, crayfish, fish, young birds, cattle egrets, beetles, grasshoppers, maggots, and worms.

These raptors hunt on the wing, from perches, and on the ground. They will also regularly patrol sections of highway in search of carrion. They may be seen feeding on road kills with vultures. They are dominant over the vultures and may occasionally chase the larger raptor from the road kill.

Caracaras may also attack or harass other avian species in order to steal their food. They may also attack other caracaras, pelicans, gulls, vultures, and other large birds. They jump on the victim's back or strike from above with the talons; the victim usually drops its prey or regurgitates its food. The caracara then dives and snatches the prey before it hits the ground.

Habitat

The Florida population commonly occurs in dry or wet prairie areas with scattered cabbage palms. It may also be found in lightly wooded areas. Scattered saw palmetto, scrub oaks, and cypress may also be present. Widespread changes in land use may have forced a change in the type of habitat this subspecies will use. The caracara now uses improved or semi-improved pasture. The presence of seasonal wetlands may be an important factor in the attractiveness of these pastures to caracaras.

Adult home ranges include one nest tree per territory. Pasture comprises the highest percentage (more than 65%) of a 328-ft (100-m) radius area around the nest tree. Citrus, row crops, mixed forest, scrub, and various wetlands comprise the remaining area. Privately-owned parcels with caracara habitat are used primarily for cattle ranching and public lands were primarily managed natural communities. A study also showed that occupancy rate, breeding rates, and nesting success were consistently higher on private lands for the three years of the study. One of the variables that may contribute to this difference in success is vegetation height. This may be related to lower predation rates in areas with less cover, or it may simply be easier for caracaras to walk around and forage in shorter vegetation. Other factors contributing to nest success may be nest tree height, and distance to major roads or human activity.

Juvenile birds have been identified in post-fledging groups in three areas. One is along the Kissimmee River, one in Glades County, and one in northern Okeechobee County. The areas appear to be primarily pasture, but further analysis of the habitat associations is underway. The juveniles will occasionally leave these loose groupings and make long excursions throughout the landscape, then return to their aggregation area. These birds have been monitored with radios, however, the study has not gone on long enough to determine what happens when these immature birds enter the reproducing population.

Distribution

The overall range of the crested caracara is from Florida, southern Texas, southwestern Arizona, and northern Baja California, through Mexico and Central America to Panama, including Cuba and the Isle of Pines. It is accidental in Jamaica. Other subspecies range into South America as far as Tierra del Fuego and the Falkland Islands.

Historically, this subspecies was a common resident in Florida from northern Brevard County, south to Fort Pierce, Lake Okeechobee, and Hendry County. It has been reported as far north as Nassau County, and as far south as Collier County and the lower Florida Keys in Monroe County. Some of the birds sighted in the Florida Keys may have been released captive animals. Available evidence indicates that the range of this subspecies in Florida has experienced a long-term continuing contraction, with birds now rarely found as far north as Orlando in Orange County or on the east side of the St. Johns River. The region of greatest abundance now is a five-county area north and west of Lake Okeechobee, including Glades, DeSoto, Highlands, Okeechobee, and Osceola counties. Birds can still be found in Charlotte, Collier, Hardee, Hendry, Polk, and St. Lucie counties and occasionally occur in Indian River, Martin, Monroe, and Palm Beach counties, although little evidence exists for breeding in these areas.

Threats

The caracara has declined throughout its range, from the early 1900s until the 1980s. It was once plentiful in Texas, and was more numerous in Arizona than it is at this time. It was considered uncommon in New Mexico and extremely rare in Oklahoma. It would appear that the distribution of the bird presently is similar to the historic distribution; however, the population size is smaller. The status in most areas where the caracara is found is largely unknown; however, it is thought to be severely declining in Mexico. It is relatively unprotected except in Florida, and is actively shot in Argentina

Caracaras in Florida have undergone a severe decline in numbers and distribution since the early 1930s although reliable data from early in the twentieth century are lacking. In 1970, fewer than 100 individual caracaras at 58 localities remained in Florida. In 1985, a more accurate estimate suggested 150 active territories with 300 adults and approximately 200 immature birds. The caracara's decline, as described in historic literature, is primarily due to habitat loss, especially its dry prairie habitat, which had been destroyed or modified for agriculture and residential development.

In addition to population declines related to habitat loss, direct human-caused mortality may be a factor in the slow recovery of the species. Caracaras may still be killed in the false belief that they prey on newborn calves. In the past, large numbers of caracaras were killed in vulture traps. Illegal trapping of vultures probably continues today. Road mortality may be a significant cause of caracara decline, especially of juvenile birds within six months of fledging. The largest single cause of mortality (primarily in immatures) is through vehicle collision.

The estimate of 300 breeding pairs of caracara in Florida is cause for concern. Because the population is isolated and habitat-specific, it is susceptible to environmental catastrophes and potentially reduced reproductive rates because of demographic accidents, such as skewed sex ratios or disproportionate age-related mortality. The caracara may also be susceptible to mass poisonings because of its scavenging habits. Low numbers may also reduce the genetic viability through loss of heterozygosity, thereby increasing vulnerability to environmental stresses. Many of the occupied territories are located on private land, and the inaccessibility of these territories to surveyors makes it difficult to census the caracara and detect changes in its population size and distribution. This difficulty increases the possibility of not detecting a population decline that could result in extirpation.

Large areas of prairie have been lost in south-central Florida to citrus operations, tree farms, improved pasture, other forms of agriculture, and real estate development. The threat from habitat loss persists as these changes in the land use continue. Human development in this area has resulted in increased numbers of roads and motor vehicles. The increase in traffic as well as the caracara's predisposition for feeding on road killed animals has probably increased this type of mortality.

Cattle ranching on large tracts of land seems to be compatible with caracara survival. The number of territories occurring in improved or unimproved pasture is expected to increase as juvenile caracaras establish their territories in similar, adjacent settings. Conversion of these areas to citrus and residential development is expected to preclude their use as nesting habitat by caracaras.

Conservation and Recovery

To date, no active conservation measures have been undertaken for the caracara in Florida. Management activities are also lacking throughout its range. Avon Park Air Force Range has conducted caracara surveys in the past. A contract has allowed a biologist to perform research both on the Avon Park Air Force Range and in the surrounding region. In considering recent biological opinions and informal consultations, the U. S. Fish and Wildlife Service has recommended to: set aside home ranges, allow research and monitoring, perform surveys, avoid work during the nesting season, and formulate a management plan for protection of the resident pair. The type of projects covered in recent opinions and consultations included conversion of pasture to citrus, a Department of Transportation road improvement project, and construction of a juvenile detention center.

Caracaras may benefit from rangeland maintenance that keeps vegetation in nest stands low. Draft habitat management guidelines similar to those in place for the bald eagle are being developed. The bald eagle guidelines have been useful in preserving bald eagle nest sites in areas subject to development pressures.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

U. S. Fish and Wildlife Service
Jacksonville Ecological Services Field Office
6620 Southpoint Drive South, Suite 310
Jacksonville, Florida, 32216-0958
Telephone: (904) 232-2580
Fax: (904) 232-2404

Reference

U. S. Fish and Wildlife Service. 1991. U. S. Fish and Wildlife Service Division of Endangered Species Species Accounts: Crested Caracara (Polyborus plancus audubonii). U. S. Fish and Wildlife Service Endangered Species Program. (http://endangered.fws.gov/i/b/sab6e.html). Date Accessed: July 10, 2000.