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BC Conservation Data Centre: Conservation Status Report

Cerorhinca monocerata
Rhinoceros Auklet

 
Scientific Name: Cerorhinca monocerata
English Name: Rhinoceros Auklet
   
Provincial Status Summary
Status: S4
Date Status Assigned: June 01, 1996
Date Last Reviewed: April 29, 2025
Reasons: This species is widespread, abundant and potentially increasing. It is a site-specific colonial nester with confirmed breeding on more than 40 islands along the coast of British Columbia. Many sites are potentially threatened by oil spills, and some are heavily impacted by alien predators but most are protected in ecological reserves or national parks from other threats. Productivity of breeding sites is heavily impacted by warm water events.
 
Range
Range Extent: F = 20,000-200,000 square km
Range Extent Estimate (km2): 158,386 square km
Range Extent Comments: Breeding: This species has been documented breeding on 45 islands in British Columbia (Rodway et al. 2016). Breeding islands are found along the entire length of British Columbia on both the inner and outer coasts for a range extent of 158,386 km2. . Many of the breeding colonies are small and there are only a few very large colonies; 89% of the total British Columbia population breeds at only seven sites (Rodway 1991, Rodway et al. 2016).

Wintering: This species winters along the coast, mostly over the continental shelf (45 to 90 km from shore) (Hipfner et al. 2020). Individuals have been shown to winter (Nov. to Feb.) over the entire continental shelf, with different breeding colonies found in different wintering areas (Hipfner et al. 2020). The species is uncommon to fairly common in winter in the Gulf Islands and the Strait of Juan de Fuca and rare in the northern Strait of Georgia (Campbell et al. 1990). The winter range is expanding with this species now wintering irregularly along the coast of BC, including Haida Gwaii north into southeastern Alaska (eBird records accessed March 2024, Audubon Society 2024b). Formerly it was thought that the majority of this species wintered from Washington State to California with small numbers wintering south to Baja California (literature reviewed in Gaston and Dechesne 2020), however recent work by Hipfner et al. (2020) using geolocator tags show that much of the winter home ranges for birds breeding in Alaska, British Columbia and on Protection Island in Washington state are staying further north than previously believed and virtually all the waters over the continental shelf are utilized. The calculated winter range extent in British Columbia is approximately 252,000 square km.
Area of Occupancy (km2): E = 26-125
Area of Occupancy Estimate (km2): 160
Area of Occupancy Comments: Rodway et al. (2016) compiled a list of the 44 islands where this species has been documented breeding in British Columbia.
 
Occurrences & Population
Number of Occurrences: C = 21 - 80
Comments: This species breeds on 44 islands along the coast of British Columbia (Rodway et al. 2016), each constituting an occurrence.
Number of Occurrences with Good Viability / Ecological Integrity: Rank Factor not assessed
Number of Occurrences Appropriately Protected & Managed: DE = 13 to >40
Comments: Virtually all large colonies and many small ones are in ecological reserves, provincial parks or national parks (Rodway et al. 2016, 2017 and 2020). The 26,000 pairs on Lucy Island are not protected.
Population Size: G = 100,000 - 1,000,000 individuals
Comments: Breeding: Rodway et al. 2016 estimated the population in British Columbia was almost 720,000 birds in 1990. Gaston and Dechesne (2020) estimated the global population at 2 to 3 million.

Wintering: Unknown, but Hipfner et al. (2020) showed that geotagged birds that bred in BC, Alaska and Washington colonies wintered further to sea and further north (including British Columbian waters) than previously believed.
 
Threats (to population, occurrences, or area affected)
Degree of Threat: C = Medium
Comments: Rodway et al. (2016) summarize threats to seabird colonies in British Columbia. Raccoon predation (Gaston and Masselink 1997, Rodway et al. 2016) and rats have resulted in declines and elimination of some colonies (Rodway et al 2016). Rodway et al (2019) review the history of rat control on seabird colonies in Haida Gwaii and discuss rat re-establishment on islands where they had been previously eradicated. Oil spills are a threat for all populations. Rhinoceros Auklet are vulnerable to oil-spill contamination because they raft on the water in large groups and have relatively small wintering areas (Bertram et al. 2023). There is overlap with regions of high vessel traffic densities, particularly within the Salish Sea. Entanglement in fish nets is also a threat, especially salmon gill-nets (Smith and Morgan 2005) although the estimated number of mortalities per year is relatively low compared to the overall population size of the species in British Columbia. Changes in vegetation cover when grass is replaced by the shrub Salmonberry can limit burrow construction by this species (Hipfner 2010).
Climate Change: Warm water years have been shown to result in low or no reproduction (Gaston et al. 2009) Several warm years in a row could have a population level effect, although a return to cooler water temperatures result in rapid return to productive conditions for Rhinoceros Auklets on Triangle Island (Gaston et al. 2009).
 
Trend (in population, range, area occupied, and/or condition of occurrences)
Short-Term Trend: GH = Relatively Stable to increase of <25%
Comments: Generation time has been calculated to be 7.084 years (Bird et al. 2020) and the 3 generation time period for a short-term trend is therefore 21.253 years.
Breeding: Possibly increasing, but available data is sparse for the most recent time period. Rodway and Lemon (2011) indicated the colonies are stable or increasing.

Wintering: Christmas Bird Count trends for this species suggest a slight decline for the most recent ten year period (Meehan et al 2022), but for the overall 21 years for short-term trends (20002-2022) the winter population is relatively stable, except for a record high number of Rhinoceros Auklets detected on the counts in the winter of 2022/2023 (Audubon Society 2024b).
Long-Term Trend: I = Increase of >25%
Comments: Breeding: Campbell et al (1990) summarizes the literature documenting the range expansion of this species in British Columbia in historical times. Percent increases in mature population size are not available. This was part of a wider range expansion with the species expanding its range in California as well (literature reviewed in Gaston and Dechesne 2020). Gaston et al. (2015) looked at trends in seabird numbers post 1970. At Triangle Island, burrow counts of all three burrow-nesting auks within study plots declined between 1984 and 2004 with Rhinoceros Auklets declining by ?0.2% per year. In contrast to observations at Triangle Island, most burrow-nesting auks breeding in Haida Gwaii increased in numbers since the 1980s, including Rhinoceros Auklets at Skaang Gwaii (4.3% per year from 1985 to 2006). The Rhinoceros Auklet population on Lucy Island, near Prince Rupert, increased by 1.7% per year between 1984 and 2006. Given that the larger colonies are further north and the increasing trends are larger in magnitude than the decreasing trends in the south the overall trend is likely an increase.
Wintering: Christmas Bird Count trends in British Columbia from 1970 to 2021 shows an increase of 3.07% per year (CI 1.10 to 5.05) (Meehan et al. 2022) or a 694% increase.
 
Other Factors
Intrinsic Vulnerability: B=Moderately vulnerable
Comments: This species lays only a single egg per season.
Environmental Specificity: C=Moderate. Generalist or community with some key requirements scarce.
Comments: Requires offshore islands to breed and only does well when they are low in predators.
Other Rank Considerations: Increasingly being impacted by changes in ocean productivity in warm water years (Gaston et al. 2016).
 
Information Gaps
Research Needs:
Inventory Needs:
 
Stewardship
Protection:
Management:
 
Version
Author: Fraser, D.F. (2024), Ramsay, L, B. Niedzielski and K. Morgan (2015)
Date: March 11, 2024
 
References
Audubon Society. 2024b. Historical Christmas Bird Count Results.
Bertram, D.F., P.D. O?Hara, A.M., King, et al. 2023. Oiling threats to marine birds on southern Vancouver Island, British Columbia, Canada. Marine Ornithology 51: 205?216.
Bird, J., R. Martin, H.R. Akçakaya, et al. 2020. Generation lengths of the world?s birds and their implications for extinction risk. Conservation Biology 34:1252?1261.
BirdLife International. 2024. Species factsheet: Cerorhinca monocerata.
Burger, A.E. 2002b. Conservation assessment of Marbled Murrelets in British Columbia: review of the biology, populations, habitat associations, and conservation (Marbled Murrelet Conservation Assessment, Part A). Tech. Rep. Ser. No. 387, Can. Wildl. Serv., Delta, BC. Online.
Campbell, R.W., N.K. Dawe, I. McTaggart-Cowan, et al. 1990. The Birds of British Columbia. Vol. 1. Nonpasserines: introduction and loons through waterfowl. Royal British Columbia Museum, Victoria, British Columbia, Canada. 514 pp.
Crewe, T. et al. 2012. Coastal waterbird population trends in the Strait of Georgia 1999?2011: Results from the first 12 years of the British Columbia Coastal Waterbird Survey. British Columbia Birds. Vol. 22, pg.8-35.
eBird. ND. eBird: an online database of bird distribution and abundance [web application]. eBird, Cornell Lab of Ornithology, Ithaca, N.Y.
Gaston, A. J. and S. B. Dechesne. 2020. Rhinoceros Auklet (Cerorhinca monocerata), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA.
Gaston, A.J., and M. Masselink. 1997. The impact of raccoons Procyon lotor on breeding seabirds in Englefield Bay, Haida Gwaii, Canada. Bird Conserv. Int. 7:35-51.
Gaston, A.J., D.F. Bertram, A.W. Boyne, J.W. Chardine, G. Davoren, A.W. Diamond, A. Hedd, W.A. Montevecchi, J.M. Hipfner, M.J.F. Lemon, M.L. Mallory, J-F Rail, and G.J. Robertson. 2009. Changes in Canadian seabird populations and ecology since 1970 in relation to changes in oceanography and food webs. Environmental Reviews 17:267-286. 
Hedd, A., D.F. Bertram, J.L. Ryder and I.L. Jones. 2006. Effects of interdecadal climate variability on marine trophic interactions: rhinoceros auklets and their fish prey. Marine Ecology Progress Series 309:263-278.
Hipfner, J.M. , M.J.F. Lemon, and M.S. Rodway. 2010. Introduced mammals, vegetation changes and seabird conservation on the Scott Islands, British Columbia, Canada. Bird Conservation International 20:295-305.
Hipfner, J.M., Prill, M.M., Studholme, et al. 2020. Geolocator tagging links distributions in the non-breeding season to population genetic structure in a sentinel North Pacific seabird. PLoS One, 15(11), p.e0240056 .
Hipfner, M. 2015. Rhinoceros Auklet in Davidson, P.J.A., R.J. Cannings, A.R. Couturier, D. Lepage, and C.M. Di Corrado (eds.). The Atlas of the Breeding Birds of British Columbia, 2008-2012. Bird Studies Canada. Delta, B.C.
Hipfner, Mark. Personal Communication. Environment Canada, Delta, BC.
Rodway, M, R.W. Campbell and M.J. Lemon. 2016. Seabird Colonies of British Columbia ? a Century of Changes. Wildlife Afield 13:1 and 2. 298 pp.
Rodway, M.S. 1991. Status and conservation of breeding seabirds in British Columbia. Pages 43-102 in J.P. Croxall, ed. Seabird status and conservation: a supplement. Int. Counc. for Bird Preservation Tech. Publ. No. 11. Cambridge. U.K.
Rodway, M.S. and M.J.F. Lemon. 2011. Use of permanent plots to monitor trends in burrow-nesting seabird populations in British Columbia. Marine Ornithology 39: 243-253.
Rodway, M.S., K. Wilson, M.J.F. Lemon, et al. 2017. The ups and downs of ecosystem engineering by burrow-nesting seabirds on Triangle Island, British Columbia. Marine Ornithology 45: 47-55.
Rodway, M.S., R.W. Campbell and M.J.F. Lemon. 2019. Seabird Colonies of British Columbia: Haida Gwaii. Wildlife Afield 16:1-479.
Rodway, M.S., R.W. Campbell and M.J.F. Lemon. 2020. Seabird Colonies of British Columbia- Outer Coast. Wildlife Afield. 17:1&2: 557 pp
Rodway, Michael. Personal Communication. Wildwing Environmental Research, Gold River, BC.
Smith, J. L. and K. H. Morgan. 2005. An assessment of seabird bycatch in longline and net fisheries in British Columbia. Technical Report Series No. 401, Canadian Wildlife Service, Pacific and Yukon Region, Delta, BC.
 

Please visit the website Conservation Status Ranks for information on how the CDC determines conservation status ranks. For global conservation status reports and ranks, please visit the NatureServe website http://www.natureserve.org/.

Suggested Citation:

B.C. Conservation Data Centre. 2024. Conservation Status Report: Cerorhinca monocerata. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 5, 2026).