Reproduction and demographic trends of Sula Leucogaster at the Moleques do Sul Archipelago, Santa Catarina, Brazil

Abstract

The Brown Booby, Sula Leucogaster, is one of the most common species of marine birds of the Brazilian coast and, in spite of being a viable subject for long-term studies, in Brazil there are scarce demographic descriptions of this species obtained from observations made in sets of consecutive years. This paper presents breeding information collected in monthly samples taken in the Moleques do Sul Island, Florianópolis, Santa Catarina, during a five year period. The main island was divided into three different study areas, in which adult censuses were conducted, along with counts of number of nests, eggs, chicks and incubating adults. No significant change was found in these numbers during the sampled years and the breeding season extended over the entire year, with a peak production of eggs and chicks from August to November. The flatter areas II and I were preferentially used, where a higher number of nests with two eggs were found. A certain number of individuals abandoned the colony outside the breeding season during some of the sampled years, which may be related to an alternation between abandonment and permanence, non-exclusive phenomena possibly associated with food availability and favorable environmental conditions. The long term knowledge of the demographic patterns and of occupation parameters of this Brown Bobby colony is essential for the conservation of the species and its habitats.