Mariana Crows (Corvus kubaryi) on Rota Island
Mariana Crow in canopyPhoto by Kevin J. McGowan

The Mariana crow, known as Aga in the Chamorro language, is an endangered species living on the island of Rota, Commonwealth of the Northern Mariana Islands (CNMI). The Mariana Crow is endemic to Guam and Rota and is the only member of the corvid family in Micronesia. On Guam, crows were considered common into the early 1960s.

Aga in captivityThe US Fish and Wildlife Service (USFWS) has been monitoring the Mariana crow on Guam and Rota for many years. The last crow known to be born on Guam was observed in 2000. Predation by introduced brown tree snakes (Boiga irregularis) is considered the main reason for the local extinction. Although tree snakes have not inhabited Rota, crow numbers have declined drastically over the past 30 years. USFWS surveys estimated 1,348 crows in 1982, but only 592 crows in 1995, a 56% decline. In 1999, there were an estimated 110 breeding pairs on Rota, but recent estimates indicate only 60 breeding pairs.


The Mariana crow has been listed as endangered by the Guam Department of Environmental and Natural Resources, USFWS and CNMI Department of Fish and Wildlife (in 1979, 1984, and 1991 respectively). The National Research Council’s Committee on Scientific Bases for Preservation of the Mariana crow independently reviewed the existing data on the crow and published their findings in 1997. In the same year, a recovery team for the species was formed, leading to the publication of a draft revised recovery plan in 2005.

On Rota, crow habitat has been protected since 1994 in the Sabana Conservation Area and the I Chenchon Bird Sanctuary. Critical habitat for the species was designated by the USFWS in 2004 (roll over map below to see extent).

Rota location in south Pacific

Our Project

The Rota population of Mariana crows has been studied since 1996 by the USFWS, CNMI biologists, and researchers from the University of Washington. This research has focused on breeding success, life history, and population dynamics. IWS has been contracted to engage in the next phase of research, focusing on reducing impacts of non-native predators by removing them from the crow's core breeding habitat. This reduction in predators will hopefully result in greater fledgling success and reduce overall predation on the crow population. We are also using motion sensor trail cameras to monitor predator movements and track the progress of removal efforts, and will be using video cameras on active crow nests to determine their fate.

The people of Rota have been very welcoming to IWS staff. We have met several landowners within our project area who are eager to grant land access to aid the project in the hope that the Aga will survive on Rota for many more generations.