Bird Conservation International

Research Articles

Reduction of first-year survival threatens the viability of the Mariana Crow Corvus kubaryi population on Rota, CNMI

JAMES C. HAa1 c1, ALYSSA BUTLERa1 and RENEE ROBINETTE HAa1

a1 Department of Psychology, University of Washington, Box 351525, Seattle WA 98195.

Summary

The Mariana Crow Corvus kubaryi is a species of forest crow originally found only on the adjacent islands of Guam and Rota in the Mariana Islands of the western Pacific Ocean. Rapid and continuing declines led to it being listed by IUCN as "Critically Endangered" in 2008. Using 97 birds marked and resighted over the course of a 21 year period, we showed there was a rapid decline in first-year (fledgling to one year old) survival from 0.7 to 0.4 between 1990 and 2010, representing a doubling in mortality, and a smaller reduction in adult survival from 0.86 to 0.82 over the same period. A population model based on Leslie matrices incorporated the effects of catastrophic events, such as typhoons and human nest removal for captive breeding. All simulations predicted a precipitous decline in future populations and the inclusion of nest removals only shortened the life of the wild population by a few years. Identifying the underlying processes behind the decline in survival is the key research priority and, given the inevitable likelihood of a continuing rapid decline, conservation action should focus on securing the future of the species through captive breeding or captive rearing of wild-born chicks and ensuring that an adaptive management conservation programme is focused on countering the factors (e.g. predation) that are currently thought to impact first-year survival and productivity. Future research may identify other causes behind the Mariana Crow's decline and the conservation programme should be flexible enough to adapt to changing needs.

(Received November 05 2008)

(Accepted May 01 2009)

Correspondence:

c1 Author for correspondence; e-mail: jcha@u.washington.edu