Blackbird, yellow-shouldered

Agelaius xanthomus

phylum: Chordata

class: Aves

order: Passeriformes

family: Icteridae

status: Endangered, IUCN Endangered, ESA

range: Puerto Rico

Description and biology

The rare yellow-shouldered blackbird is similar to its North American relative the red-winged blackbird. Its body is 7 to 9 inches (18 to 23 centimeters) long and dark gray in color. A distinctive yellow patch on its shoulder gives the bird its common name. Females are smaller than males. The bird eats mainly insects that it forages from plants and the leaves, branches, and bark of trees.

The birds nest in colonies and defend the immediate territory around their nests. Unlike many other blackbird species, the yellow-shouldered blackbird is monogamous (has just one mate for life). Mating usually takes place in April or May. The female lays 2 to 3 eggs and incubates (sits on or broods) them for 12 to 14 days before they hatch. After the nestlings are born, the female and male both share in gathering food.

There are two subspecies of yellow-shouldered blackbird: the Puerto Rico yellow-shouldered blackbird (Agelaius xanthomus xanthomus) and the Mona yellow-shouldered blackbird (Agelaius xanthomus monensis). Both subspecies are considered endangered.

Habitat and current distribution

Puerto Rico yellow-shouldered blackbirds nest in coconut palms and mangroves, most often on offshore islets (very small islands) around Puerto Rico. Approximately 400 of the birds exist on and around the island.

Mona yellow-shouldered blackbirds are found on Mona Island, which lies between Puerto Rico and Hispaniola (the island divided between Haiti on the west and the Dominican Republic on the east). These birds nest on the ledges or in the crevices of sheer coastal cliffs. Their population numbers between 400 and 900.

History and conservation measures

The Puerto Rico yellow-shouldered blackbird was once abundant throughout coastal areas of Puerto Rico. It was found in various habitats, including freshwater wetlands, open woodlands, and fields. In the 1970s, its population was estimated at over 2,000.

Biologists (people who study living organisms) believe habitat destruction—mainly the draining of almost all the wetland areas in its range—was the initial cause of the bird's decline. The Puerto Rico yellow-shouldered blackbird continues to be threatened by mongooses, rats, and other mammals that eat its eggs. A more recent threat is the shiny cowbird. This bird, introduced to the region in the 1950s, slyly lays its eggs in the blackbird's nest. When the female blackbird returns, she broods on both her eggs and the cowbird's eggs. After the eggs hatch, the larger cowbirds dominate the smaller blackbirds, eating more of their food and often pushing them out of the nest.

The Mona yellow-shouldered blackbird is also currently threatened by habitat destruction (caused by increasing human development of Mona Island) and the shiny cowbird.

Controlling the cowbird population in the region and developing protected areas such as Puerto Rico's Boquerón Commonwealth Forest are measures conservationists have undertaken to help the yellow-shouldered blackbird recover.