Yellow-shouldered Blackbird

Conservation History.  In the mid-1800s, the Yellow-shouldered Blackbird was described as “excessively abundant” around San Juan and thrived in various habitats across Puerto Rico and Vieques.  A combination of human persecution as a perceived agricultural pest, nest predation by rats and mongoose, and brood parasitism by Shiny Cowbirds drastically reduced its numbers to a low of approximately 300 in 1982, almost all in the far southwest, and none on Vieques.  Conservation efforts, including cowbird control measures, helped stem the decline and have resulted in significant increases—to approximately 1,000 birds in recent years—although its numbers continue to fluctuate significantly from year to year.

In the 1980s and 90s, three breeding populations remained on Puerto Rico, all nesting colonially on mangrove islands.  By far the largest occupied several sites along the southwest coast.  A second group remained in the southeast in the Jobos Bay National Estuarine Research Reserve between Salinas and Guayama.  In 2012, the southwestern population was estimated at 650, and the Jobos Bay population was approximately 100.

The third Puerto Rican population was a small flock that nested at the eastern tip of the island in the Ceiba Natural Reserve State Forest (formerly part of Roosevelt Roads Naval Station), but reportedly vanished in the late 1990s.  Recent sightings around Ceiba and Fajardo suggest that the species is recolonizing that area, or that this tiny population never disappeared entirely.

On Mona Island, censuses of known roosting sites during the 1990s counted between 153 and 310 individuals, and the overall population estimate was 400.  Counts on Monito during the breeding season have been approximately 25 birds (i.e., about ten to twelve nesting pairs).

Although the remnant populations of Yellow-shouldered Blackbird have peculiar nesting habits that make the species as a whole appear highly specialized, this appears to be a recent development that arose because its other breeding strategies proved more vulnerable to predation, parasitism, and human interference.  Apart from being a social breeder, the Yellow-shouldered Blackbird is not as limited as its small range suggests.  It has recently shown a high tolerance for human development, which may provide a path to long-term recovery.