Yellow-shouldered Blackbird Agelaius xanthomus

  • Order: Passeriformes
  • Family: Icteridae
  • Polytypic: 2 subspecies
  • Authors: William Post

The Yellow-shouldered Blackbird is a conspicuous songbird of coastal Puerto Rico. Its local name is "mariquita," which means "ladybird." Once common at lower elevations throughout Puerto Rico, it now is concentrated in the mangrove zone of southwestern Puerto Rico, and in xeric scrub on Mona Island; several small populations are scattered in other areas of the Puerto Rican mainland. The Yellow-shoulder is the primary host of a brood parasite, the Shiny Cowbird (Molothrus bonariensis), which arrived in Puerto Rico in 1955, or earlier. Cowbird numbers increased rapidly because of favorable (disturbed) habitats. By 1976, nearly all blackbird nests on the Puerto Rican mainland contained cowbird eggs. Brood parasitism caused significant reduction in Yellow-shoulder nesting success. Yellow-shoulder numbers on Puerto Rico were estimated to be 2400 in 1975, but had dwindled to less than half that number by 1983. The blackbird was classified as endangered in 1976. Cowbird control and habitat management, started in 1980, improved nesting success, and numbers in southwestern Puerto Rico have begun to recover. Cowbird eggs have not been found on Mona Island yet, and Yellow-shoulder numbers (about 700) have remained stable. Although most mainland birds now nest in mangroves, the Yellow-shoulder is a habitat generalist that also nests in suburbs, towns, coastal scrub and savannas. On Mona Island it nests on coastal cliffs. It is monogamous and nonterritorial; pairs defend only a small nest-centered area. The blackbird has many displays and vocalizations related to intersexual communication. This large repertoire is reflected by strong mate fidelity: even after repeated nest failures, pairs remain together, often moving to new, distant locations. Its varied diet is composed of arthropods, nectar, fruit and seeds, usually obtained in trees and shrubs, and also grains and human foods taken at ground level.


© José A. Colón López

  • Year-round
  • Migration
  • Breeding
  • Non-Breeding

Recommended Citation

Post, W. (2011). Yellow-shouldered Blackbird (Agelaius xanthomus), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA.