observed, the chewing louse (formerly classified as Mallophaga), with three species being observed: Philopterus agelaii; Machaerilaemus species; and Myrsidea species. The parasites predominantly occur in the head area with adult males having the highest infestation percentage and juveniles having a lower infestation rate than adults. The mites Ornithonyssus bursa and Androlaelaps casalis have also been observed in nests, but the information presently available does not indicate they are a threat. Another disease commonly experienced by yellow-shouldered blackbirds is fowlpox, also known as avian pox. Lesions caused by this disease occur in exposed areas such as the legs and the bend of the wings. Nest predation has been an important contributor to the decline of the yellow-shouldered blackbird. Known terrestrial predators include rats (Rattus rattus), mongooses and feral cats, all introduced species to Puerto Rico. Rats constituted the main nest predator eating both eggs and hatchlings. A 1983 report concluded that rat predation accounted for 48% of nest failures that year. The majority of the activity coincided with the recession of water from July to August which exposed the mangrove nesting area to dry land. Since the middle 1980s artificial PVC nesting structures have been created in mudflats surrounding mangrove forests to reduce rat predation. These structures replaced old wooden nesting boxes and were readily accepted by the species. Presently, few (one or two) natural nests are observed each year in the area. The loss of feeding and breeding habitat and brood parasitism by the shiny cowbird are among other threats that limit and endanger the yellow-shouldered blackbird populations. Natural predators, such as the pearly-eyed thrasher (Margarops fuscatus), also represent a threat, although minor, to the populations. These animals have been reported to steal eggs and young from nests and to also destroy or steal nesting materials which in many cases leaves the young as prey for the predators. See also Fauna of Puerto Rico List of birds of Puerto Rico List of endemic fauna of Puerto Rico List of Puerto Rican birds List of Vieques birds El Toro Wilderness References yellow-shouldered blackbird yellow-shouldered blackbird Endemic birds of Puerto Rico yellow-shouldered blackbird yellow-shouldered blackbird ESA endangered species