breeding activity has been observed from February to November. The breeding season's start coincides with the start of the rainy season, thus explaining the fluctuation in the start and end of the breeding season. The species is believed to be monogamous with a single attempt at nesting per year and with nesting being performed in loose colonies. Nests of both the nominate form and the Mona subspecies contain from one to four eggs with an average of three. Eggs are blue-green with brown spots and are incubated for 13 days by the female. Both sexes reach sexual maturity at one year of age. As with other Agelaius species, it usually builds open, cup-shaped nests in trees, but nest locations and shapes may vary depending on location and availability of building materials. The Roosevelt Roads' population builds nests on hollows in dead mangroves, while the Mona subspecies builds nests in ledges or crevices near the coastal cliffs. In all, the species uses eight distinct nesting habitats: mudflats and salinas; offshore red mangrove cays; black mangrove forest; lowland pastures (dry coastal forest); suburban areas; coconut plantations; and coastal cliffs. Building of the nest is performed solely by females while feeding of the young is performed by both sexes. Nestlings leave the nest 13 to 16 days after hatching. Males defend small territories, usually around 3 metres, during the nesting period. Before the nesting period males defend slightly larger territories to repel other males. Yellow-shouldered blackbirds engage in anting, a rare behavior only observed in the Puerto Rican tanager among West Indian birds. Individuals were observed applying Pheidole species ants to their body and feathers for a short period of time (8 minutes). The species engages in mobbing, a behavior in which a pack of birds, from one or more species, attack a known predator (usually to defend eggs or hatchlings). Threats and conservation efforts The yellow-shouldered blackbird was listed as an endangered species on November 19, 1976, by the U.S. Fish and Wildlife Service. Critical habitat was subsequently established for the entire Mona and Monito islands, the Roosevelt Roads Naval Station in Ceiba, an area expanding from Cabo Rojo to Guánica in the southwest region of Puerto Rico, and a small area in San Germán. Diseases such as avian pox have been associated with extinction of bird populations such as Hawaiian honeycreepers. For this species only one type of parasite has been