Snail Kite (Rostrhamus sociabilis) Science Article 3


The breeding biology of the Snail Kite was studied in Florida from 1968-1977 and intermittently from 1978-1980. Breeding occurred every month, but not in the same year. Peak egg-laying occurred from February through April or generally about 81 d before the onset of the rainy season in mid- or late May. Courtship displays, copulation, and duration of copulation are described. Mean egg-laying interval was 2.2 d, and clutch size ranged from 1-6 eggs ( = 2.92). The frequency of large clutches (4-6 eggs) was significantly greater before 1940 than after. Incubation, which was shared by both sexes, lasted 24-30 d ( = 27.4). Egg length and breath, the eggshell thickness and weight, and whole egg volume and weight are presented. Hatching success was 57.5%. Mean hatching success for all clutches was 1.7 young or 2.3 per successful clutch. Hatching success of 2- and 3-egg clutches did not differ significantly. The nestling period averaged 28.7 d (range 23-34). The interval between fledging of the first and last nestling in 1 brood was up to 5 d. An averageo f 2.0 young were raised per successful nest, and 50.5% of the nests were successful. The mean percent of successful nests per year for the 11-yr period( excluding the drought year 1971 in which there was no nesting) was 56.5 (range 17.1-84.6/yr). Nestling mortality was 37% overall, but was less during favorable high water conditions. Twenty-two factors are identified as causing nesting failure in kites, principal among these was predation (44%)

PauI W. Sykes, jr, J. Field Ornithol., 58(2):171-189

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