This range-restricted species is confined to the lowlands of southwestern Puerto Rico. Two races are recognized. This is the nominate subspecies found in mangroves and adjacent areas on the mainland. Another race (A. x. monensis) is confined to Mona Island off Western Puerto Rico. It has more extensive white rather than yellow median coverts and also paler yellow coloration. This photo shows that the nominate race may also show some white trim in the otherwise yellow median coverts.
The yellow is usually hidden under black scapulars, but is revealed in flight and in courtship display. Immatures have black median coverts and look entirely black when perched. Males and females are similar.
This species was formerly abundant but is now rare and critically endangered. The total population was reduced to only 300 birds by 1982 and current estimates are about 900 on the mainland (Cavalliery et al. 2011) with an additional 700 on Mona Island (HBW 2011).
The cause of the decline appears to be brood parasitism by Shiny Cowbirds which arrived in Puerto Rico from South America around 1955 (Oberle 2010). A conservation program started in 1980 has reduced the number of parasitized Yellow-shouldered Blackbird nests from 87% to 8% with fledging rates increasing from 0.3 to 2.3 birds per nest (Jaramillo and Burke 1999).
Digiscoped with Panasonic DMC-LZ5 | Nikon FieldScope III | 30XWA | hand-held (no adapter)