The Breeding Ecology of Sea Birds on Monito Island, Puerto Rico

Abstract

Monito Island, a 15 ha plateau surrounded by steep undercut cliffs, lies halfway between Puerto Rico and the Dominican Republic. Of the 9 sea birds [Phaethon lepturus, Sula dactylatra, S. leucogaster S. sula, Fregata magnificens, Larus atricilla Sterna anaethetus, Sterna fuscata and Anous Stolidus], are known to breed and 2 (blue-faced booby [S. dactylatra] and laughing gull [L. atricilla] are here recorded as breeders in Puerto Rico for the 1st time. The Pelecaniformes are represented by 5 spp., the white-tailed tropicbird, the 3 pan-tropical boobies, and the magnificent frigatebird. The boobies all have long but annual breeding seasons, from fall through spring, showing a distinct breeding hiatus in the hot summer months, although some latenesters may care for chicks during this period. The magnificent frigatebird has the most synchronous breeding, with a laying peak from late Oct. to early Dec., when 70% of the population lays eggs. Four larids (laughing gull, bridled tern, sooty tern, and brown noddy) are summer residents vacating the island in Aug.-Sept. and returning again in March-April. In general, they nest during the pelecaniform non-breeding season. The sea birds show a great range in nest site preference, with little overlap among them. Their diversity results from a combination of isolation, rugged cliffs, and the structural diversity of Monito Island. Although currently one of the outstanding sea bird colonies in the West Indies, Monito is threatened, and the colonies could be lost unless they are legally protected.