Conservation and Management

Shooting And Trapping

Minimal impacts (Sprunt 1945).

Pesticides And Other Contaminants/Toxics

Sykes (1985b), 1970–1977, found measurable levels of DDE (0.03–0.34 parts per million [ppm]), DDD (ND–0.20 ppm), and DDT (ND–0.06 ppm) in 9 eggs; dieldrin and PCB residues were < 0.1 ppm. PCBs ranged from trace to 0.11 ppm in muscle tissue. J. A. Rodgers (unpubl. data, 1992–1993) also found low concentrations of DDD (ND–0.05 ppm), DDE (ND–0.05 ppm), lead (ND–0.17 ppm), and mercury (ND–0.35 ppm) in 11 eggs; no detectable levels of DDT, dieldrin, heptachlor, trans-nonachlor, or PCBs were found. These pesticides and heavy-metal concentrations are considered baseline levels and probably pose no immediate hazard to Snail Kites in Florida. Arsenic detected in relatively high levels (0.02–0.08 ppm) in apple snails near Palm Beach Water Catchment Area marsh where Snail Kites breed and feed (Solid Waste Authority Palm Beach Co. 1991); effects unknown but merit further investigation.

Environmental Contaminants

All contaminant residues (DDT, DDD, DDE, dieldrin, PCBs, mercury, lead, and arsenic) reported from tissues (whole carcass, muscle, brain, liver, and kidney) of Snail Kites (adults, nestlings, and eggs) and apple snails in Florida (1966–1993) have been low, with no significant accumulations; all considered baseline readings in the environment at that time (Stickel et al. 1969, 1970, 1984, Lamont and Reichel 1970, Wiemeyer et al. 1980, Pattee et al. 1981, Sykes 1985b, N. J. Thomas, D. J. Forrester, and M. G. Spalding unpubl. data, JAR). Other chemical contaminants tested for but not detected in Snail Kites in Florida include chlordane, trans-nonachlor, oxychlordane, cis-chlordane, cis-nonachlor, endrin, toxaphene, heptachlor epoxide, mirex, and hexachlorobenzene (Sykes 1985b, D. J. Forrester and M. G. Spalding unpubl. data, JAR). Sodium pentachlorophenol (NaPCP) used in Surinam rice fields in 1971 to control freshwater snails (Pomacea glauca and P. lineata) resulted in a die-off of Snail Kites, and analysis of bird carcasses (n = 17) attributed mortality to the chemical (Vermeer et al. 1974).

Ingestion Of Plastics, Lead, Etc

No known impact.

Collisions With Stationary/Moving Structure Or Objects

Rare. Can safely negotiate objects, but 3 cases of collisions with vehicles reported (REB).

Fishing Nets

No known impact.

Degradation Of Habitat: Breeding And Wintering

Degradation of breeding and wintering foraging habitat is primary negative impact in Florida. Alteration of natural hydrocycle, dewatering wetlands, and eutrophication cause breeding failure and decreased productivity. Alteration of natural hydrocycles and water quality reduced area of littoral-zone marsh for foraging on Lake Kissimmee. Similar activities on Lake Okeechobee have increased frequency of lower lake levels, resulting in less foraging habitat, forcing Snail Kites to nest frequently in nonwoody vegetation (e.g., cattail), which is more susceptible to nest collapse. Run-off and back-pumping from surrounding agricultural areas have resulted in eutrophic waters at Lakes Kissimmee and Okeechobee and water conservation areas. This has brought rapid growth of cattail, water hyacinth, water bonnets, and hydrilla (Hydrilla verticillata), causing loss of foraging habitat. Indirect application of herbicides to these aquatic plants has caused the collapse of nests in nonwoody substrates (e.g., cattail) at Lakes Kissimmee and Okeechobee during latter 1980s. Low lake levels force Snail Kites to nest near open water, increasing interaction with humans (e.g., fishing, boating, frog hunting, aquatic plant control, etc.).

Disturbance At Nest And Roost Sites

Most pairs nest in dense isolated marshes, so disturbance is generally low. Pairs that nest along boat trails are frequently flushed from their nests (Sykes 1987c), however, and occasionally nests are run over by airboats. Fires set on Lake Okeechobee can destroy nests (Sykes 1987c). Low water levels on lakes force Snail Kites to nest near open water, where they are more vulnerable to disturbance by fishing activities. Roosts occasionally are disturbed by frog hunting at night in water conservation areas and Lake Okeechobee. Roosts or nests during drought can be close to human development.

Human/Research Impacts

This species is generally tolerant of researchers and fishing/boating activities while foraging, but can be sensitive to disturbance near nests, particularly during early stages of nesting.

Conservation Status

Protected by the Migratory Bird Treaty Act (federal), Endangered Species Act (federal), and Chapter 39, Florida Administrative Code (state) which prohibit taking or harassing adults, nests, eggs, or nestlings. Federal and state listing as Endangered affords species additional protection from development and environmental impacts.

Measures Proposed And Taken

Snail Kite Recovery Plan approved in 1983 and revised in 1986 (U.S. Fish Wildl. Serv. 1983, 1986). Section 7 Consultation (Federal agencies required to consult with U.S. Fish and Wildlife Service to avoid jeopardizing continued existence of Threatened/Endangered species) occurs when Snail Kites are potentially jeopardized by impacts to habitat in Florida. Statewide surveys conducted since late 1960s provide good index of Snail Kite population trends. New breeding and wintering range generally detected because of continuous coverage by researchers from 1960s to 1990s and interest by birders and breeding bird atlas work in Florida. Seminal work by Roderick Chandler, National Audubon Society, placed Snail Kite nests in protected structures at Lake Okeechobee in early 1970s, greatly increasing productivity when population was low (Sykes and Chandler 1974).

Species benefitted from prolonged impoundment schedules in the water conservation areas (= Everglades habitat) and Upper St. Johns Water Management Areas. Will also benefit from planned higher water levels on Lake Kissimmee if implemented in later 1990s. Should benefit from restoration of littoral zone/riparian habitat along Kissimmee River in 1990s. Would benefit from fewer water releases and higher water levels at Lake Okeechobee; levels of 4.65 m would inundate 90% of littoral zone and allow nesting in flooded woody vegetation (reducing nest collapse) and provide more foraging habitat (higher nestling survivorship). Species has benefitted from aquatic plant control of water hyacinth, water bonnets, and hydrilla; control maintains shallow open-water foraging habitat. Maintenance of areas closed to herbicide application around nests in nonwoody substrates, however, is an important cooperative program between South Florida Water Management District and Florida Game and Fresh Water Fish Commission on Lakes Kissimmee and Okeechobee. Infrequent late fall-winter lake drawdowns to improve water quality and littoral zone vegetation benefit Snail Kites. Primary environmental need is to reduce nutrient loads contributing to eutrophication of water quality and invasion of undesirable aquatic plants that affect foraging habitat.

Effectiveness Of Measures: The Species’ Response

Species recolonized Lake Kissimmee, Lake Tohopekaliga, E. Lake Tohopekaliga, St. Johns marshes, and West Palm Beach Water Management Area after low water levels associated with drought conditions at Lake Okeechobee and water conservation areas forced dispersal from traditional habitats in 1980s. Snail Kites respond well in wetlands with prolonged inundation schedules (e.g., water conservation areas) and after lake drawdowns (e.g., Lakes Tohopekaliga, Kissimmee, and Okeechobee). Higher lake levels allow Snail Kites to nest farther back in marshes away from human activities and in more stable woody vegetation, but high lake levels kill woody vegetation. Furthermore, periodic drying of marshes is a necessary part of the maintenance of Snail Kite habitat and occurs naturally in some years.