Florida Snail Kite

Rostrhamus sociabilis plumbeus

Description

The Rostrhamus sociabilis plumbeus (Florida snail kite), also known as the Everglade kite, is a snail-eating hawk with an average body size of 17 in (43 cm) and a wingspan of about 47 in (120 cm). The adult male is slate gray, shading into black, with black wing tips and head. The slightly larger female is dark brown above with a white forehead and throat. The squared tail of both sexes is white with a broad black band and lighter terminal band. Legs are red-orange and the eyes red. Immature birds of both sexes resemble the adult female.

The snail kite is in the subfamily Accipitrainae, comprising the true kites. Four subspecies were originally recognized: the Everglade snail kite (Rostrhamus sociabilis plumbeus ) of peninsular Florida; the Cuban snail kite (Rostrhamus sociabilis levis ) of Cuba and the Isle of Pines; the Mexican snail kite (Rostrhamus sociabilis major ) of eastern Mexico, northern Guatemala, and northern Belize; and the South American snail kite (Rostrhamus sociabilis sociabilis ) of Nicaragua, Honduras, Costa Rica, and the southern coast. In 1975, the populations in Florida, Cuba, and the Isle of Pines were combined into one subspecies (Rostrhamus sociabilis plumbeus ).

Behavior

The Florida snail kite feeds almost exclusively on one species of freshwater mollusk, the apple snail, which is found in shallow, open-water areas of the Everglades. The kite patrols low over the marsh with a great deal of wing-flapping as it searches for snails; it dives and captures snails by extending its feet before it into the water. The bird's hooked bill is ideally suited to removing the snail from its shell.

Kites nest over water in trees, shrubs, or cattails. Cattails are used when trees or shrubs are not available, and nests may fall if buffeted by winds. Although the kite can nest throughout the year, the main nesting period is from January through August. Kites reach breeding age at ten months. The usual clutch of three eggs is incubated by both parents for about 30 days. Young fledge in 23-28 days and are tended by both parents. Florida snail kites are not monogamous. One of a pair will usually abandon the young about three to five weeks before its mate. Birds are gregarious and somewhat nomadic, usually dispersing after nesting.

Habitat

The kite prefers areas of shallow open water, such as sloughs and marshes, that remain wet throughout the year. The depth of the water can fluctuate as long as the bottom does not dry out. The apple snail feeds on marsh plants among saw-grass or cattails, and regular seasonal flooding is needed to sustain an adequate snail population.

Distribution

The Florida snail kite once ranged throughout the Florida peninsula, Cuba, and the Isle of Pines in the Caribbean. The Caribbean populations are not considered to be in jeopardy.

The snail kite nests in Lake Okeechobee's western marshes, Loxahatchee National Wildlife Refuge, the St. Johns River headwaters reservoir, lakes Kissimmee and Tohopekalig in central Florida, and the northern part of the Everglades National Park.

Wandering birds have been recorded at other sites as far north as Duval, Wakulla, and Marion counties in Florida. During high-water years, kites have been observed in the Big Cypress National Preserve. During drought years, as in 1981-1982, kites disperse over much of Florida, ranging as far north as Dixie, Marion, and Hillsborough counties in search of food sources.

Populations were estimated at 668 birds in 1984, but after the drought of 1985 only 407 birds were surveyed. In the 1990s, surveys produced counts of from 378 to 996 individuals. The population of the Florida snail kite has stabilized since the 1970s, and in recent years, has shown evidence of an increase, due in part to wet habitat conditions.

Threats

The Everglade snail kite is threatened primarily by the destruction and degradation of its wetland habitat. Widespread drainage associated with agricultural and residential development has permanently lowered the water table in some areas, destroying kite habitat. In addition, large areas of formerly open-water wetlands have become heavily infested with the non-native water hyacinth (Eichornia crassipes ), which forms dense floating mats unsuitable for feeding by the Everglade snail kite. Other threats include shooting and excessive disturbance near its nests. It has also been affected by the degradation of its food supply by agricultural runoff containing pesticides and nutrients, and may have suffered direct toxicity from insecticides.

Conservation and Recovery

The main threat to the Florida snail kite is loss of its habitat and its principal food source. The draining of south Florida's wetlands for agriculture and for residential development began in the early 1900s and continues at a rapid pace today. Increased demand on the freshwater supply has lowered water levels and dried out wetlands, restricting the habitat of the apple snail, and, consequently, the snail kite.

While the kite is adapted to natural drought cycles, large-scale water control regimens worsen the effects of dry periods. Since 1925 Lake Okeechobee water levels, for example, have become more seasonal, variable, and significantly lower. Drought-flood cycles have been shortened from ten or more years to five or six years, and the snail population has declined.

Water pollution also poses a serious threat to the Florida snail kite and the apple snail. Pesticides applied from the air to orchards and fields often drift into the marsh. Toxins accumulate in the apple snail and are passed on to the kite.

Several species of introduced plants are also altering the habitat. An exotic water hyacinth that forms dense mats on the water surface makes it impossible for kites to hunt. The Australian punktree can rapidly invade snail kite habitat, changing it from open marsh to dense stands of trees.

The National Audubon Society leases about 11,330 hectares (28,000 acres) on the west side of Lake Okeechobee, containing one of the snail kite's principal nesting areas. The society has relocated kite nests to artificial nest structures to prevent loss to heavy wind and rain.

The U.S. Fish and Wildlife Service (FWS) does not believe that the Florida snail kite can ever be delisted because of the continuing loss of habitat. However, in its 1986 Recovery Plan the FWS stated that an average population of 650 birds for a 10-year period, with annual declines of less than 10%, would warrant reclassifying the Florida snail kite from Endangered to Threatened.

In June 1989, the Interior Department created a new wildlife refuge for the Florida panther and other endangered species in south Florida. The 12,140 hectare (30,000 acre) Florida Panther National Wildlife Refuge is adjacent to the Big Cypress National Preserve and provides protected habitat for the Endangered wood stork (Mycteria americana ), bald eagle (Haliaeetus leucocephalus ), peregrine falcon (Falco peregrinus anatum ), and eastern indigo snake (Drymarchon corais couperi ), as well as the Florida snail kite.

Overall, the FWS sees the recovery efforts for the Florida snail kite as a relative success. While the kite was primarily restricted to an area south of Lake Okeechobee in the late 1970s, it has reestablished itself in much of its historic range. Kites are now found breeding and feeding in the Kissimmeee Chain of Lakes area and the marshes of the Upper St. John's River. While the bird still requires Endangered Species Act protection, the FWS is working on criteria for reclassifying the bird to the improved category of Threatened.

Contact

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

References

Amadon, D. 1975. "Variation in the Everglade Kite." Auk 92:380-382.

Beissinger, S. R., and J. E. Takekawa. 1983. "Habitat Use by and Dispersal of Snail Kites in Florida During Drought Conditions." Florida Field Naturalist 11:89-106.

Sykes, P. W., Jr. 1984. "The Range of the Snail Kite and Its History in Florida." Bulletin of Florida State Museum, Biological Science 29(6):211-264.

U.S. Fish and Wildlife Service. 1986. "Florida Snail Kite Revised Recovery Plan." U.S. Fish and Wildlife Service, Atlanta.