Corvus kubaryi

Taxonomy

Assessment Information

Geographic Range

Population

Habitat and Ecology

Threats

Conservation Actions

Bibliography

View Printer Friendly

Taxonomy [top]

Kingdom	Phylum	Class	Order	Family
ANIMALIA	CHORDATA	AVES	PASSERIFORMES	CORVIDAE

Scientific Name:

Corvus kubaryi

Species Authority:

Reichenow, 1885

Common Name/s:

English

–

Guam Crow, Mariana Crow

Assessment Information [top]

Red List Category & Criteria:

Critically Endangered A2bcde+3bcde+4bcde;C2a(ii) ver 3.1

Year Published:

2010

Assessor/s:

BirdLife International

Reviewer/s:

Butchart, S., Calvert, R. & Symes, A.

Contributor/s:

Camp, R., Lepson, J., Morton, J., Rodda, G., Saunders, A., Wiles, G. & de Cruz, T.

Justification:
This species qualifies as Critically Endangered because surveys have shown that it is declining extremely rapidly. It now has an extremely small population and is effectively confined to just one island where multiple factors are driving the decline. Urgent conservation measures are required to ensure that this species does not become extinct.

History:

2009	–	Critically Endangered
2008	–	Critically Endangered
2004	–	Endangered
2000	–	Endangered
1996	–	Critically Endangered
1994	–	Critically Endangered

Geographic Range [top]

Range Description:	Corvus kubaryi inhabits Guam (to USA) and Rota in the Northern Mariana Islands (to USA). On Guam, it was formerly common but, since the 1960s, declined in numbers and area inhabited³ with an estimated 350 birds in 1981¹, less than 40 in 1995³, and seven in 1999. Following introduction of birds from Rota the population rose to 16 in 2001¹⁰, but has since declined to four (all males)¹⁵. On Rota, it was thought to be stable, estimated at 1,318 birds in 1982², but has since declined to 592 in 1995³, and then to 234 in 1998^6,14; in 2007 there were c.50 confirmed pairs and a few more suspected¹⁵, and the population in 2008 stood at around 85 pairs¹⁶. Three birds are held in captivity⁷. Surveys on Rota between 1982 and 2004 indicated a decline of 93%¹⁶. Apparent survival analysis of birds ringed between 1990 and 2010 revealed that the rate of first-year survival fell from 70% to 40% over that period, roughly equivalent to a doubling in the rate of mortality; this was accompanied by a slight decrease in adult survival over the same period¹⁸. Population modelling using the most recent estimate for apparent survival in first-year birds predicts extinction of the species in 75 years, with models that incorporate the removal of birds for captive breeding and the impact of catastrophic events projecting more rapid declines¹⁸.
Countries:	Native: Guam; Northern Mariana Islands
Range Map:	Click here to open the map viewer and explore range.

Population [top]

Population:	In 2008 only two males remained on Guam (Berry et al. in litt. 2008). On Rota, the population was estimated at 234 mature indiviuals in 1998 by Plentovich (2005) and there were only 60 confirmed pairs recorded in 2008 (Berry et al. in litt. 2008), hence the band 50-249 seems appropriate.
Population Trend:	Decreasing

Habitat and Ecology [top]

Habitat and Ecology:	It inhabits mature and second growth forest and coastal strand vegetation⁵ but probably only nests in native forest⁶. It forages in the forest canopy, understorey and occasionally on the forest floor for seeds, fruit, arthropods and lizards⁵.
Systems:	Terrestrial

Threats [top]

Major Threat(s):	On Guam, its decline was due to predation by the introduced brown tree snake Boiga irregularis and, despite protection of nest-sites by electrical tree barriers, it is now effectively extinct there⁸. On Rota, recent typhoons have devastated forest habitat and forest has been cleared for homestead development, resort and golf-course construction and agricultural settlement; actions which are often accompanied by direct persecution (shooting)^4,8,10,14. Additional threats include nest-predation/disturbance by introduced rats Rattus spp. and monitor lizard Varanus indicus, competition with introduced Black Drongo Dicrurus macrocercus and disease^6,16. Feral cats, amongst other predators, have been implicated in the falling apparent survival rate of first-year birds¹⁸. Brown tree snake is not yet established on Rota, but if a snake population becomes established an even more serious decline is likely. Having a distribution on relatively low-lying islands, this species is potentially susceptible to climate change through sea-level rise and shifts in suitable climatic conditions¹⁷.

Major Threat(s):

On Guam, its decline was due to predation by the introduced brown tree snake Boiga irregularis and, despite protection of nest-sites by electrical tree barriers, it is now effectively extinct there⁸. On Rota, recent typhoons have devastated forest habitat and forest has been cleared for homestead development, resort and golf-course construction and agricultural settlement; actions which are often accompanied by direct persecution (shooting)^4,8,10,14. Additional threats include nest-predation/disturbance by introduced rats Rattus spp. and monitor lizard Varanus indicus, competition with introduced Black Drongo Dicrurus macrocercus and disease^6,16. Feral cats, amongst other predators, have been implicated in the falling apparent survival rate of first-year birds¹⁸. Brown tree snake is not yet established on Rota, but if a snake population becomes established an even more serious decline is likely. Having a distribution on relatively low-lying islands, this species is potentially susceptible to climate change through sea-level rise and shifts in suitable climatic conditions¹⁷.

Conservation Actions [top]

Conservation Actions:	Conservation Actions Underway On Guam, a National Wildlife Refuge was established in 1993 to preserve remaining forest⁹, and birds are being translocated from Rota in an effort to maintain the wild population on the island. A 40 ha snake-free area created on North-west field is available for the introduction of crows, and an adjacent larger area is being readied for the translocation of Rota crows¹². A predation control experiment will soon be starting on Rota, which may include demographic work in the future. A grant has been obtained for a Habitat Conservation Plan for Rota's Agricultural Homesteads, which will increase the amount of land in protected areas¹³. Biological control for the brown tree snake is also being investigated¹². On Rota, life history studies are currently being conducted and there are proposals to protect vital tracts of forest under a Habitat Conservation Plan^8,10. Research is being conducted into the fate of nests through the use of remote cameras and the fate of juveniles by using radio-tags¹⁸. Conservation Actions Proposed Implement stringent measures to prevent the spread of B. irregularis from Guam to Rota^8,10. Continue research including study of population biology and health of marked birds^6,8. Conduct annual censuses using standardised methodology^6,8,10. Continue nest protection and increase trapping of Rattus spp. and Varanus indicus in adjacent areas⁸. Begin control of Dicrurus macrocercus and feral cats. Facilitate the enactment of the proposed Habitat Conservation Plan^6,8,10. Conduct a public education programme to reduce persecution⁸. Introduce more stringent controls for construction projects. Study the causes of nest failure and first-year mortality¹⁸. Assess the feasibility of a captive-breeding programme¹⁸.

Conservation Actions:

Conservation Actions Underway
On Guam, a National Wildlife Refuge was established in 1993 to preserve remaining forest⁹, and birds are being translocated from Rota in an effort to maintain the wild population on the island. A 40 ha snake-free area created on North-west field is available for the introduction of crows, and an adjacent larger area is being readied for the translocation of Rota crows¹². A predation control experiment will soon be starting on Rota, which may include demographic work in the future. A grant has been obtained for a Habitat Conservation Plan for Rota's Agricultural Homesteads, which will increase the amount of land in protected areas¹³. Biological control for the brown tree snake is also being investigated¹². On Rota, life history studies are currently being conducted and there are proposals to protect vital tracts of forest under a Habitat Conservation Plan^8,10. Research is being conducted into the fate of nests through the use of remote cameras and the fate of juveniles by using radio-tags¹⁸.

Conservation Actions Proposed
Implement stringent measures to prevent the spread of B. irregularis from Guam to Rota^8,10. Continue research including study of population biology and health of marked birds^6,8. Conduct annual censuses using standardised methodology^6,8,10. Continue nest protection and increase trapping of Rattus spp. and Varanus indicus in adjacent areas⁸. Begin control of Dicrurus macrocercus and feral cats. Facilitate the enactment of the proposed Habitat Conservation Plan^6,8,10. Conduct a public education programme to reduce persecution⁸. Introduce more stringent controls for construction projects. Study the causes of nest failure and first-year mortality¹⁸. Assess the feasibility of a captive-breeding programme¹⁸.

Bibliography [top]

	Amar, A.; Amidon, F.; Arroyo, B.; Esselstyn, J. A.; Marshall, A. P. 2008. Population trends of the forest bird community on the Pacific island of Rota, Mariana Islands. Condor 110(3): 421-427. Beck, R. E. Jnr; Savidge, J. A. 2000. Mariana Crow. In: Reading, R.P.; Miller, B. (ed.), Endangered animals: a reference guide to conflicting issues, pp. 191-195. Greenwood Press, London. Engbring, J.; Pratt, H. D. 1985. Endangered birds in Micronesia: their history, status and future prospects. In: Temple, S. A. (ed.), Bird Conservation, pp. 71-105. University of Wisconsin Press, Madison, U.S.A. Engbring, J.; Ramsey, F. L.; Wildman, V. J. 1982. Micronesian forest bird survey, 1982: Saipan, Tinian, Agiguan, and Rota. U.S. Fish and Wildlife Service, Honolulu. Fancy, S. G.; Lusk, M. R.; Grout, D. J. 1999. Status of the Mariana Crow population on Rota. Micronesica 32: 3-10. Michael, G. A. 1987. Notes on the breeding biology and ecology of the Mariana or Guam Crow. Avicultural Magazine 93: 73-82. Morton, J. M.; Plentovich, S.; Sharp, T. 1999. Reproduction and juvenile dispersal of Mariana Crows (Corvus kubaryi) on Rota 1996-1999. National Research Council. 1997. The scientific bases for preservation of the Mariana crow. National Academy Press, Washington, DC. Plentovich, S.; Morton, J.M.; Bart, J.; Camp, R.J.; Lusk, M.; Johnson, N.; Vanderwerf, E. 2005. Population trends of Mariana Crow Corvus kubaryi on Rota, Commonwealth of the Northern Mariana Islands. Bird Conservation International 15: 211-224. Wiles, G. J.; Aguon, C. F.; Davis, G. W. 1995. The status and distribution of endangered animals and plants in northern Guam. Micronesica 28: 31-49.

Amar, A.; Amidon, F.; Arroyo, B.; Esselstyn, J. A.; Marshall, A. P. 2008. Population trends of the forest bird community on the Pacific island of Rota, Mariana Islands. Condor 110(3): 421-427.

Beck, R. E. Jnr; Savidge, J. A. 2000. Mariana Crow. In: Reading, R.P.; Miller, B. (ed.), Endangered animals: a reference guide to conflicting issues, pp. 191-195. Greenwood Press, London.

Engbring, J.; Pratt, H. D. 1985. Endangered birds in Micronesia: their history, status and future prospects. In: Temple, S. A. (ed.), Bird Conservation, pp. 71-105. University of Wisconsin Press, Madison, U.S.A.

Engbring, J.; Ramsey, F. L.; Wildman, V. J. 1982. Micronesian forest bird survey, 1982: Saipan, Tinian, Agiguan, and Rota. U.S. Fish and Wildlife Service, Honolulu.

Fancy, S. G.; Lusk, M. R.; Grout, D. J. 1999. Status of the Mariana Crow population on Rota. Micronesica 32: 3-10.

Michael, G. A. 1987. Notes on the breeding biology and ecology of the Mariana or Guam Crow. Avicultural Magazine 93: 73-82.

Morton, J. M.; Plentovich, S.; Sharp, T. 1999. Reproduction and juvenile dispersal of Mariana Crows (Corvus kubaryi) on Rota 1996-1999.

National Research Council. 1997. The scientific bases for preservation of the Mariana crow. National Academy Press, Washington, DC.

Plentovich, S.; Morton, J.M.; Bart, J.; Camp, R.J.; Lusk, M.; Johnson, N.; Vanderwerf, E. 2005. Population trends of Mariana Crow Corvus kubaryi on Rota, Commonwealth of the Northern Mariana Islands. Bird Conservation International 15: 211-224.

Wiles, G. J.; Aguon, C. F.; Davis, G. W. 1995. The status and distribution of endangered animals and plants in northern Guam. Micronesica 28: 31-49.

Citation:	BirdLife International 2010. Corvus kubaryi. In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. <www.iucnredlist.org>. Downloaded on 22 May 2012.
Disclaimer:	To make use of this information, please check the <Terms of Use>.
Feedback:	If you see any errors or have any questions or suggestions on what is shown on this page, please fill in the feedback form so that we can correct or extend the information provided