On Guam, the Mariana crow's decline is primarily due to predation by the introduced brown tree snake ("Boiga irregularis"). In spite of protection of nesting-sites by electrical tree barriers, the remaining birds are considered to be reproductively senescent. On Rota, many other threats endanger the crow, including homestead development, resort and golf-course construction, agricultural settlement, nest-predation from introduced rats, the mangrove monitor lizard ("Varanus indicus"), typhoons, predation from feral cats, disease, and competition with the black drongo ("Dicrurus macrocercus"). More recently, the brown tree snake has also been detected on Rota, likely leading to serious declines in the Mariana crow population there if the snake population establishes itself. The Mariana crow is also persecuted by residents of both islands who see it as an obstacle to development.