Abstract
Sterna hirundinacea (Lesson, 1831) is a migratory seabird that breeds in the Pacific Coast (from Peru to Chile) and along the Atlantic coast of South America from Espírito Santo (Brazil) to Terra del Fuego (Argentina). This paper describes the reproductive success of South American Terns on Cardos Island, Florianopolis, Brazil in the breeding seasons of 2003, 2005 and 2006. The colony was formed in mid-May in 2003 and early April in other years, with the total number of nests ranging from 1,852 in 2006 to 2,486 in 2005. Hatching success was estimated at 76.39% in 2006, 62.73% in 2003 and 41.1% in 2005, the lowest value that could be attributed to predation by hawks Caracara plancus, lizards Tupinambis merianae and black vulture Coragyps atratus. The chicks hatched in July in 2003, and in June 2005 and 2006, and fledging success was 50.94%, 35.96 and 53.47% respectively. Cardos Island has been constantly used as a breeding site by South American Terns, and therefore represents an important area for conservation of this species. This success could be attributed to low pressure of Kelp gulls (Larus dominicanus), the main predator of seabirds along the Brazilian coast.
Highlights
The reproductive success of coastal seabirds is often low, but varies between and within sites and seasons due to the influence of climate, availability of food, predation, occurrence of catastrophic events (Mcnicholl 1982), vegetation succession, competition with other species, pollution and human development (Hébert 1985)
Marine terns are usually more vulnerable than other coastal species such as gulls, because they are more specialized in terms of breeding and foraging grounds, and have
Despite the extensive coastline in both countries, breeding of both species is concentrated in only a small number of sites (Yorio and Efe 2008)
Summary
The reproductive success of coastal seabirds is often low, but varies between and within sites and seasons due to the influence of climate, availability of food, predation, occurrence of catastrophic events (Mcnicholl 1982), vegetation succession, competition with other species, pollution and human development (Hébert 1985). South American and Cabot’s Terns (Thalasseus sandvicensis eurygnathus (Saunders, 1876) breed together mostly in Brazil and Argentina (Gochfeld and Burger 1996). The main threats faced by these two species in both countries appear to be human disturbance, fisheries, egging and expanding Kelp Gull (Larus dominicanus) populations (Yorio and Efe 2008), but the information regarding brazilian colonies is largely limited to regional reports on status and distribution (Sick and Leão 1965, Soares and Schiefler 1995, Sick 1997, Efe et al 2000, Branco 2003a, b, Alves et al 2004, Campos et al 2004, Krul 2004)
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