Snail Kite (Rostrhamus sociabilis)

Snail Kite

[order] ACCIPITRIFORMES | [family] Accipitridae | [latin] Rostrhamus sociabilis | [authority] Vieillot, 1817 | [UK] Snail Kite | [FR] Milan des marais | [DE] Schneckenweih | [ES] Caracolero Comun | [NL] Slakkewouw

Subspecies

Monotypic species

Genus

The Snail Kite, Rostrhamus sociabilis, is a bird of prey within the family Accipitridae, which also includes the eagles, hawks, and Old World vultures. Its relative, the Slender-billed Kite, is now again placed in Helicolestes, making the genus Rostrhamus monotypic. Usually placed in the milvine kites, the validity of that group is under investigation. This genus has a uniform dark plumage and a highly specialized beak.

Physical charateristics

The snail kite is a medium-sized raptor, with a total body length for adult birds of 36 to 40 cm and a wingspan of 109 to 116 cm. In both sexes, the tail is square-tipped with a distinctive white base, and the wings are broad, and paddle-shaped. Adults of both sexes have red eyes, while juveniles have brown eyes. The slender, decurved bill is an adaptation for extracting the kite’s primary prey, the apple snail; the bill is a distinguishing character for field identification in both adults and juveniles. Sexual dimorphism is exhibited in this species, with adult males uniformly slate grey and adult females brown with cream streaking in the face, throat, and breast. Most adult females have a cream superciliary line and cream chin and throat. Females are slightly larger than males. Immature snail kites are similar to adult females but are more cinnamon-colored with tawny or buff-colored streaking rather than cream streaking. The legs and cere of females and juveniles are yellow to orange; those of adult males are orange, turning more reddish during reeding.
Non-breeding snail kites use communal roosts throughout the year in association with other birds, particularly anhingas (Anhinga anhinga), herons, and vultures. The snail kite can nest solitarily, but more often in uneven clusters, and often hunts in close proximity without defending a foraging territory. However, defense of feeding territories, outside of the breeding season, occurs more often than previously thought; typically, however, these birds display no territorial behavior and feeding areas overlap.

Listen to the sound of Snail Kite

[audio:http://www.planetofbirds.com/MASTER/ACCIPITRIFORMES/Accipitridae/sounds/Snail Kite.mp3]

Copyright remark: Most sounds derived from xeno-canto


wingspan min.: 109 cm wingspan max.: 116 cm
size min.: 36 cm size max.: 40 cm
incubation min.: 24 days incubation max.: 30 days
fledging min.: 28 days fledging max.: 30 days
broods: 1   eggs min.: 2  
      eggs max.: 5  

Range

North America, Latin America : South Florida and Caribbean to Northeast Argentina

Habitat

Snail kite habitat consists of freshwater marshes and the shallow vegetated edges of lakes (natural and man-made) where apple snails can be found. These habitats occur in humid, tropical ecoregions of peninsular Florida and are characterized as palustrine-emergent, long-hydroperiod wetlands often on an organic peat substrate overlying oolitic limestone or sand or directly on limestone or marl. Suitable foraging habitat for the snail kite is typically a combination of low (< 3 m) marsh with shallow (0.2-1.3 m deep) open water, which is relatively clear and calm.

Reproduction

Pair bonds are formed by a series of behaviors with each nesting. Males often begin construction of the nest prior to attracting a mate. Materials are gathered with feet or bill and are carried in the bill one piece at a time to the nest site. The nest is a bulky loosely woven structure of dry sticks and other dry plant
material. Thirty-two species of plants are known to be used in construction, with sticks from willow and wax myrtle the most common material. Snail kites often use green nest material, especially the upper lining that forms a cup for holding the eggs; this functions to insulate the otherwise porous structure of dry sticks. Males display either in the air or at perch near the chosen nest site. Aerial displays often include carrying a stick in the bill and vocalizing; these displays may include skydance or undulating flight, deep wing beats, pendulum, mutual soaring, tumbling, and grappling.
The male may feed the female a snail or bring her a stick. In Florida, most pair bonds form from late November to early June. Once a pair bond is established, the female may spend time at or near the nest site and may assist the male in completing the nest. Copulation can occur from early stages of nest construction, through egglaying, and during early incubation if the clutch is not complete. Egg laying begins soon after completion of the nest or is delayed a week or more. An average 2-day interval between laying each egg results in the laying of a three egg clutch in about 6 days. The clutch size is 1 to 5 eggs, with a mode of three. Incubation may begin after the first egg is laid, but generally after the second egg. In Florida, the incubation period lasts 24 to 30 days. Incubation is shared by both sexes, but the sharing of incubation time between sexes varies among nests.
The breeding season varies widely from year to year in relation to rainfall and water levels. Ninety-eight percent of the nesting attempts are initiated from December through July, while 89 percent are initiated from January through June. Snail kites often renest following failed attempts as well as after successful attempts, but the actual number of clutches per breeding season is not well documented.
The mating system of snail kites is characterized by sequential polygamy (ambisexual mate desertion). Desertion occurs in years with abundant food supply, but not during drought years. The deserted mate continues to tend the nest until independence of the chicks, which is for another 3 to 5 weeks. Young are fed through the nestling period and after fledging until they are 9 to 11 weeks old. Chicks assume food begging postures and vocalizations when the tending adult approaches the nest with a snail. As the chicks mature, the food progresses from pieces of torn snail fed bill to bill, whole snails removed from the shell and with operculum removed, to completely intact snails. When food is scarce, larger siblings may dominate the food supply brought to the nest. While rearing young, the adults forage no more than six km from the nest, and generally less than a few hundred meters.

Feeding habits

The snail kite feeds almost exclusively on snails. The snail kite uses two visual foraging methods: course-hunting, while flying 1.5 to 10 m above the water surface, or still-hunting from a perch. While course-hunting, the flight is characterized by slow wing beats, alternating with gliding; the flight path is usually into the wind, with the head oriented downward to search for prey. Snails are captured with the feet at or below the surface, to a maximum reach of approximately 16 cm below the surface. Snail kites do not plunge into the water to capture snails and never use the bill to capture prey. Individuals may concentrate hunting in a particular foraging site, returning to the same area as long as foraging conditions are favorable. Capture rates are higher in summer than in winter, with no captures observed at a temperature less than 10 degrees C. Snail kites frequently transfer snails from the feet to the bill while in flight to a perch. Feeding perches include living and dead woodystemmed plants, blades of sawgrass and cattails, and fence posts. The snail kite is known to feed on the introduced snail Pomacea bridges. On rare occasions, snail kites in Florida prey on small turtles. Snail kites have also been observed feeding upon crayfish and a speckled perch.

Video Snail Kite

httpv://www.youtube.com/watch?v=ILc9sytFl0o

copyright: A. Garca


Conservation

This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
Snail Kite status Least Concern

Migration

Southernmost populations migratory, although transition between migratory and resident populations not documented; otherwise nomadic in response to droughts or drainage of feeding areas. Leaves South Brazil in April, returning in September, some birds moving to Pantanal, where large numbers move South in loose flocks. Occasionally wanders to lower temperate zone in Andes. Will commute over large distances between feeding and nesting areas.

Distribution map

Snail Kite distribution range map

Literature

Title Notes on the Snail Kite in Surinam.
Author(s): F. HAVERSCHMIDT
Abstract: The coastal plain of Surinam the Snail Kite (Rostr..[more]..
Source: The Auk 87(3):580-584

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Title Snail Kite Kleptoparasitism of Limpkins
Author(s): BRUCE W. MILLER AND RONALD L TILSON
Abstract: Kleptoparasitism is defined as the stealing of foo..[more]..
Source: The Auk 102: 170-171

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Title SOME ASPECTS OF THE BREEDING BIOLOGY OF THE SNAIL KITE IN FLORIDA
Author(s): PauI W. Sykes, jr
Abstract: The breeding biology of the Snail Kite was studied..[more]..
Source: J. Field Ornithol., 58(2):171-189

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Title MOLLUSK PREDATION BY SNAIL KITES IN COLOMBIA
Author(s): NOEL F. R. SNYDER AND HERBERT W. KALE
Abstract: Snail Kites (Rostrhamus sociabilis sociabilis) obs..[more]..
Source: The Auk 100: 93-97. January 1983

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Title HUNTING BEHAVIOR, PREY SELECTION, AND ENERGETICS OF SNAIL KITES IN GUYANA: CONSUMER CHOICE BY A SPECIALIST
Author(s): STEVEN R. BEISSINGER
Abstract: The hunting behavior, snail size selection, and ti..[more]..
Source: The Auk 100:84-92 January 1983

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