- Habitat loss
- Nest predation
- Mortality through parasites and diseases
The Yellow-Shouldered Blackbird is a Puerto Rican endemic blackbird species that also goes by the name la Mariquita de Puerto Rico or capitán.
This diurnal insectivore, which used to flourish within the coastal forests of Puerto Rico, is one of the few passerine birds which engage in a bird maintenance activity called ‘anting’ wherein ants are rubbed on its feathers and skin.
It also participates in anti-predatory adaptation activity called ‘mobbing’ wherein it unites with other bird species to attack a known predator as a way of defending its eggs or hatchlings.
Many parts of the lowlands where the Yellow-Shouldered Blackbird feeds have already been converted for sugar cane production and other agricultural activities since the early 20th century. There are also limited options for nesting habitats as more and more mangroves are being destroyed. The remaining mangrove areas are also heavily affected by pollution which makes it uninhabitable and puts the Yellow-Shouldered Blackbird in a vulnerable situation where it is defenseless against rats and other carnivore predators. Competition over nest habitats due to the presence of the Shiny Cowbird species also leads to low reproduction of the Yellow-Shouldered Blackbird. Population growth is also difficult due to the presence of avian pox disease.