Snail Kite Life History

Habitat

Snail Kites occur chiefly in freshwater marshes, lakes, retention ponds, sloughs, wet prairies, borrow pits, and canals. In southern Florida, typical aquatic vegetation includes sawgrass (the classic Everglades plant), duckweed, water lettuce, white water-lily, pickerel weed, floating heart, spikerush, maidencane, arrowhead, water fern, and water hyacinth, while emergent vegetation at the edges is often cattail, giant bulrush, or Phragmites. If aquatic vegetation is extensive, kites, which hunt visually, cannot see the snails and sometimes abandon otherwise suitable habitats. Similarly, they avoid areas with murky water. Surrounding their foraging wetlands are often tropical woodlands with willow, holly, cypress, wax myrtle, and other trees. Snail Kites rest and roost together, usually in clumps of coastal-plain willow at the water’s edge. During droughts, when snails become more difficult to find, Snail Kites sometimes wander in search of other wetlands.

Food

Snail Kites feed almost entirely on freshwater apple snails (genus Pomacea). These include both the native Florida apple snail (P. paludosa) and non-native snails recently introduced to Florida, such as the island apple snail (P. maculata) and spike-topped apple snail (P. diffusa). Snail Kites forage from perches or while flying slowly above shallow, clear, open water, watching for snails. They drop onto snails and seize them in the talons (never the bill), then perch before extracting the snail with the bill. Snail Kites sometimes try to steal apple snails from Limpkins. On rare occasions, Snail Kites take other prey such as small freshwater turtles, crayfish, snakes, or fish. In South America, Snail Kites eat other types of snails as well as small crabs.

Nesting

Nest Placement

The male appears to select the nest site, in trees beside (or growing in) shallow water, usually adjacent to feeding areas. Trees are usually less than 30 feet tall; some kites also build nests on shrubbery or emergent vegetation such as sawgrass. Pairs also use pole-mounted nest baskets placed in marshes by biologists.

Nest Description

The male constructs the bulky nest, but the female helps maintain it, a mass of dry sticks and other plant materials, usually willow and myrtle branches, and lined with green leaves, reeds, and grasses. Nests average about 16 inches across and 9 inches tall, with interior cup about 6 inches across and 2.4 inches deep.

Nesting Facts

Behavior

As the nesting season approaches, male Snail Kites begin aerial courtship displays. They perform undulating “roller coaster” flights and exaggeratedly slow “butterfly” flights near prospective mates, often while carrying a stick in the bill and calling. Females sometimes join males in the sky, occasionally locking talons and tumbling downward. Males also entice females with courtship feeding and by giving them sticks. On rare occasions, small groups of kites display together—these are probably younger birds learning and practicing. Snail Kites are monogamous, and both male and female share incubation duties and nest defense. Both mates chase away other kites that approach the nest too closely, even though this species nests in loose colonies when nesting habitat and snails are plentiful. Males often feed incubating females. Both parents also feed and defend the young; however, once the young approach the age of fledging, one parent often stops attending the nest, and in many cases, this parent then re-partners and nests again. This mating system is termed “sequential monogamy.” Careful studies of nesting kites in Florida have demonstrated that females and males abandon partners in equal proportions and that young birds fledge successfully whether one parent or two parents attend them. After nesting, most kites roost in the evening with herons, ibises, vultures, Wood Storks, or Anhingas. Occasionally, hundreds of kites roost together. Some kites disperse long distances after the nesting season, but most return to nest near whey they hatched (called “natal philopatry”). During very cold winters, some kites in central Florida move southward into southern Florida, but otherwise the species is not migratory.

Conservation

The U.S. population of Snail Kites is estimated at 1,000 birds and is listed as endangered both federally and in Florida. The size of the Florida population has varied greatly, from a low of about 65 birds in 1972 to a high of about 3,000 in 1999. These numbers represent a tiny fraction of this species’ population in Florida prior to widespread destruction of freshwater wetlands in the nineteenth and twentieth centuries. In Central and South America, Snail Kites are common, but populations still tend to vary greatly according to water levels and apple snail numbers. Partners in Flight estimates a global breeding population of 2 million and rates the species a 9 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. The Florida population is possibly at risk from chemical pollutants (from agriculture and industry) and from bacterial disease, a subject of ongoing research. Although the species was nearly extirpated in the United States during the twentieth century by the draining of the Everglades, the Comprehensive Everglades Restoration Plan has restored some of the area’s natural water flow north of Everglades National Park. This massive conservation effort may continue to benefit kite populations in years to come.

Credits

Lutmerding, J. A. and A. S. Love. Longevity records of North American birds. Version 2015.2. Patuxent Wildlife Research Center, Bird Banding Laboratory 2015.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Reichert, Brian E., Christopher E. Cattau, Robert J. Fletcher, Jr., Paul W. Sykes Jr., James A. Rodgers Jr. and R. E. Bennetts. (2015). Snail Kite (Rostrhamus sociabilis), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, USA.

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