Age at First Breeding
Approximately one third of Snail Kites breed at one year of age. By 5 years of age, there is over a 50% chance that any given Snail Kite has attempted to breed and by 25 years of age that chance is approximately 75% (Reichert, 2009).
Lifespan and Survivorship
Snail Kites have been reported to live up to 25 years of age, and can successfully reproduce until they are about 18 years old (Reichert, 2009). Annual adult survivorship is approximately 0.9, suggesting an average life expectancy of 9.5 years (Brownie et al., 1985; Bennetts et al., 1999). Annual survival of juvenile Snail Kites is significantly lower than that of adults, approximately 0.66. The greatest drop in survivorship of juvenile Snail Kites occurs in late spring. This may be attributed to the period in which parents stop attending their fledged young and the young must disperse and search for food on their own (Bennetts, 1999). While the primary changes in response to localized drought (1-5 years) is only behavioral, widespread and long-term droughts can make habitats be less suitable and thus local population survivorship and reproduction rates decline (Sykes, 1983).
Diseases and Body Parasites
Two specimens collected in Florida in 1993 were infected with Bothrigaster variolaris, a trematode flatworm (Cole et al., 1995). Other flatworms, such as those of the genus Athesmia, have also infected Snail Kites (Lunaschi et al., 2009). Ornithonyssus mites have been found on Snail Kite chicks in the nest (Phillis et. al., 1976). No blood parasites have been found in Snail Kites (Sykes et al., 1983).
Snail Kites are nonmigratory, although nonbreeding birds disperse widely on a frequent basis. However, in Florida they tend to move towards the south part of their range during cold winters (U.S. Fish and Wildlife Service, 1999). In addition to seasonal changes in temperature, Snail Kites may also move in response to changes in water depth, food availability, and hydroperiod (Sykes, 1978, 1983; Beissinger et al., 1983, Bennetts et al., 1994). For example, in Lake Okeechobee, Florida, in 1983, the resident Snail Kite population dispersed throughout the Florida peninsula in response to a drought event (Beissinger et al. 1983).
Juvenile dispersal typically occurs after 30-60 days after fledging (Bennetts et al., 1999).