Northern Mariana Islands: Endangered Mariana Crow population rebounds on Rota

RNZ News

23-05-2025

Mariana Crow, known as 'Aga' in Chamorro.
Photo:
Marianas Press
The endangered Mariana Crow, known as "Aga" in Chamorro, is showing strong signs of recovery, with 70 breeding pairs now thriving in the wild on Rota.
That figure represents approximately 300 individual birds, a significant milestone toward the species' downlisting and eventual removal from the endangered species list.
Rota Avian Behavioral Ecology Program's primary investigator Sarah Faegre told
Marianas Press
that the conservation effort is in a critical and optimistic phase.
"This is a very exciting time to be here on Rota," Faegre said.
"We are seeing high rates of reproduction among the captive-reared birds that have been released into the wild."
Since 2017, the San Diego Zoo Wildlife Alliance and the University of Washington have collaborated to rear and release 90 captive-raised Mariana Crows.
Back in 2013, there were only 46 known breeding pairs.
Photo:
Supplied
These birds now make up 20 percent of the breeding population, and this year alone, they have already produced four fledglings.
"It's significant because it means the birds we rear and release are not only surviving, but they're also displaying normal social behavior-they're pairing and reproducing in the wild, which is exactly what we need them to do," Faegre said.
The Mariana Crow is a long-lived species, and Faegre noted that some of the birds released in 2017 are only now beginning to breed.
"We saw a long delay. For a while, we were concerned about lower rates of reproduction, but even if it takes five or six years, they are breeding now," she said. "We're expecting to see the population increase faster going forward."
Back in 2013, there were only 46 known breeding pairs.
The recent rise to 70 brings the Rota population within reach of the US Fish and Wildlife Service's criteria for downlisting: 75 stable or increasing breeding pairs on Rota.
"We could reach that 75-pair mark in just a few more years," Faegre said.
However, full delisting requires not only maintaining 75 pairs on Rota, but also establishing a second viable population on another island. That means future conservation efforts may include translocating birds to other locations within the Marianas.
While the progress is promising, challenges remain.
"The biggest threat to the Aga is a poorly understood inflammatory syndrome that's killing young birds," Faegre said.
Pathologists have been researching the syndrome since 2011 but have yet to determine its cause. One possibility is an autoimmune response triggered by mosquito-borne pathogens or high mosquito density.
Other risks include potential future land-use conflicts with local populations, and the looming danger of the brown tree snake being introduced to Rota-an invasive species that has devastated native bird populations in Guam.
Despite these concerns, Faegre said the focus remains on growth and recovery.
"We are on the cusp of something really important," she said. "This species has a chance-not just to survive, but to thrive again."
The San Diego Zoo Wildlife Alliance operates a rear-and-release facility on Rota in partnership with the University of Washington. Their joint program continues to play a critical role in the recovery of one of the Marianas' most iconic and culturally significant birds.