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Rhinoceros Auklet Cerorhinca monocerata

Justification
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

Taxonomic source(s)
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.

Distribution and population
The Rhinoceros Auklet is found in the North Pacific and breeds from California, USA, off the coasts of Canada and Alaska to the Aleutian Islands in North America; and on Hokkaido and Honshu, Japan, as well as on the northern tip of North Korea, Sakhalin (Russia) and at two places on the far eastern Siberian coast in Asia (del Hoyo et al. 1996).

Population justification
The global population is estimated to number > c.1,300,000 individuals (del Hoyo et al. 1996), while national population estimates include: < c.1,000 wintering individuals in Korea; c.10,000-1 million breeding pairs c.1,000-10,000 wintering individuals in Japan and c.10,000-100,000 breeding pairs in Russia (Brazil 2009).

Trend justification
The population is suspected to be in decline owing to predation by invasive species.

Ecology
Habitat: This marine species cab ne found both offshore and along sea coasts and islands. It breeds on maritime and inland grassy slopes, sometimes on predator-free islands, and rarely on steep island or mainland cliffs. It occurs in large aggregations at sea, often forming dense roosting flocks at night in sheltered bays. In winter it is normally pelagic in waters offshore from breeding areas and sometimes in near-shore coastal waters where food is highly concentrated due to oceanographic conditions. Diet: It feeds mostly on fish throughout the year supplemented in winter by small amounts of invertebrates such as squid and krill. Chick diet it almost exclusively fish though also invertebrates for late-hatching young. Breeding: It arrives at colonies in late March and early April, laying from the end of April to mid-June. It is monogamous with high site and mate fidelity. It is highly colonial in small to very large concentrations sometimes over 100,000 individuals. Laying is often highly asynchronous within a colony. Birds lay in nest chambers at the end of a burrow which are excavated by both sexes (del Hoyo et al. 1996).

Related state of the world's birds case studies

References
Bertram, D. F.; Mackas, D. L.; McKinnell, S. M. 2001. The seasonal cycle revisited: interannual variation and ecosystem consequences. Progress in Oceanography 49: 283-307.

Brazil, M. 2009. Birds of East Asia: eastern China, Taiwan, Korea, Japan, eastern Russia. Christopher Helm, London.

del Hoyo, J.; Elliott, A.; Sargatal, J. 1996. Handbook of the Birds of the World, vol. 3: Hoatzin to Auks. Lynx Edicions, Barcelona, Spain.

Wilson, U. W. 2005. The effect of the 1997-1998 El Niño on rhinoceros auklets on protection island, Washington. Condor 107: 462-468.

Further web sources of information
Explore HBW Alive for further information on this species

Search for photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Ekstrom, J., Butchart, S., Calvert, R.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2014) Species factsheet: Cerorhinca monocerata. Downloaded from http://www.birdlife.org on 30/09/2014. Recommended citation for factsheets for more than one species: BirdLife International (2014) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 30/09/2014.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Key facts
Current IUCN Red List category Least Concern
Family Alcidae (Auks)
Species name author (Pallas, 1811)
Population size mature individuals
Population trend Decreasing
Distribution size (breeding/resident) 321,000 km2
Country endemic? No
Links to further information
- Additional Information on this species