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The Status of Rhinoceros Auklet (Cerorhinca monocerata) in California
Julie A. Thayer and Kyra Mills, Marine Ecology Division, PRBO Conservation Science

Special Concern Priority
Currently considered a California Bird Species of Special Concern (breeding), Priority 3.



Banding a Rhinoceros Auklet.

General Range and Abundance

No subspecies are recognized. Breeds along the Pacific coast of North America from the Aleutian Islands, Alaska, south to southern California, and along the Pacific coast of Asia in N. Korea, northern Japan, Sakhalin and the southern Kuril Islands (1,2). During the breeding season, it occurs in waters from the outer continental shelf to well beyond the shelf break. During the non-breeding season, ranges widely at sea from southern Alaska south to southern California and southern Japan. World population estimates are extremely rough at 1.5 million breeding birds, with approximately 1 million in the North American segment (1). Most (>95%) of the North American population breeds on islands in SE Alaska (12%), British Columbia (73%) and Washington (13%), with most concentrated at 8 colonies (1).

Rhinoceros Auklet in flight.		 Seasonal Status in the California Current

The breeding season extends from early April to early September during which time birds are present in waters off California, Oregon and Washington. Birds may arrive at colonies as early as January to begin preparations for breeding. Following breeding, birds disperse south to important wintering areas off California and numbers decline to low levels in the northern two states in winter (3,4). There is also a shift from waters over the continental shelf and at the shelf break during breeding (3,5) to waters seaward of the shelf off California in winter (4), although this species also winterns in canyon habitats such as Monterey Bay.
Historical and Recent Range and Abundance in California

Rhinoceros Auklet breeding populations were extirpated from California circa 1860 (6). Over the past 30 years Rhinoceros Auklets have re-colonized the historic range (7,8,9,10,11). Numbers remain low, however, as the most recent counts estimated approximately 1,700 individuals breeding in California (10). These 1989 estimates included 30 sites (10,11) although the majority occurred at only 3 main colonies: Castle Rock (502 pairs); South Farallon Islands (257 pairs); and Aņo Nuevo Island (33 pairs)(10). Estimates are rough because of the difficulty censusing this nocturnal, cavity-nesting species. The above estimate at Aņo Nuevo Island may have been low, as a burrow occupancy of 50% was used to create the estimate, but recent studies have indicated a much higher occupancy rate of self-excavated sand or soil burrows, between 70-95% (PRBO unpublished data). Recent population estimates on Aņo Nuevo Island have peaked at 123 pairs, largely due to burrow protection measures and installation of artificial burrows (J. Thayer/PRBO unpublished data). No updated population estimates are currently available for other colonies in California, however, at Castle Rock and Southeast Farallon Island recent declines are suspected (see "Threats" below).


Rhinoceros Auklet burrow (foreground) on Aņo Nuevo Island near old abandoned Lightkeeper's House.

 Ecological Requirements

Despite the name, Rhinoceros Auklets are more closely related to puffins than to auklets. Rhinoceros Auklets breed primarily in burrows that they dig, although they will also nest in natural rock crevices, caves, or suitably-placed nest boxes (12,13,14). At most colonies, Rhinoceros Auklets are nocturnal or crepuscular, although diurnal activity has been observed on Southeast Farallon Island (9). Birds return to natal regions to breed between ages 3-5 (PRBO unpublished data), and pairs often remain together in successive years (15).
Rhinoceros Auklets are wing-propelled, pursuit-diving birds, and their diet in California consists mainly of schooling mid-water fishes and squid (13,16,17,18,19). Prey composition is somewhat variable among colonies and inter-annually. On offshore Southeast Farallon Island in 1987-2000 main food for chicks included Northern anchovy (Engraulis mordax), Pacific saury (Cololabis saira), squid (Loligo opalescens); and juvenile rockfish (Sebastes spp.), sablefish (Anoplopoma fimbria) and king salmon (Oncorhynchus tshawytscha)(19), with rockfish becoming increasingly important in the past two years (PRBO unpublished data). On nearshore Aņo Nuevo Island, between 1993-2000 main prey included anchovy, and to a lesser extent saury, rockfish and squid (13,18), but similarly, rockfish dominated the diet in 2001-2002 (PRBO unpublished data).


A school of Sardines.


Oiled puffins, a close relative of the Rhinoceros Auklet.

 Threats to California Populations

Documented and potential threats to the Rhinoceros Auklet populations in California include exotic mammalian species, oil and chemical contamination, fisheries interactions, human disturbance, burrow trampling, habitat degradation, predation and climate change. Historically, extirpations may have been influenced by introduced mammalian predators such as domestic pets, and competitors, such as the European hare, that may have out-competed Rhinoceros Auklets for nesting space (9). The effect of oil spills on Rhinoceros Auklets has been studied at numerous locations (20,21,22,23,24,25) and the species' vulnerability is well known. Rhinoceros Auklet was the second most impacted species in the Apex Houston oil spill off central California, with approximately 1,600 individuals killed or debilitated (21). Other contaminants such as heavy metals and organochlorines may be of concern in Rhinoceros Auklets. Egg samples from central California have shown elevated PCB and mercury levels (26).

Disturbance and trampling of burrows by humans, pinnipeds, and surface nesting or roosting birds (cormorants, pelicans, geese) can cause nest loss, lowered reproductive success, and even adult death (13,28, J. Thayer pers. obs.). Loss of vegetation and erosion of nesting habitat has increased on Aņo Nuevo Island and is suspected on Castle Rock, further compromising burrow integrity. The number of burrows damaged due to soil erosion during the nesting season on Aņo Nuevo Island has increased from 11% in 1997 to 56% in 2001 (J. Thayer/PRBO unpublished data). In recent years, vegetation loss and erosion at Castle Rock has been caused by thousands of Aleutian Canada geese (Branta canadensis leucopareia) that roost there during spring migration (29).


Entrance tunnel to Rhicnoceros Auklet nest box providing protected breeding site in denuded habitat on Aņo Nuevo Island.


Peregrine Falcon.

Predation is a moderate to serious threat at some colonies. Mortality has been documented at Southeast Farallon Island and Aņo Nuevo Island from peregrine falcons (Falco peregrinus) and owls (PRBO unpublished data). Adult survival is important for sustainable populations in long-lived species such as Rhinoceros Auklets. Observed predation at nearshore Aņo Nuevo Island has ranged from 1%-10% of the population each year in the past ten years (PRBO unpublished data). Survival of adults between 1993-2001 was ~79%, much lower than at offshore Southeast Farallon Island or than other alcid species such as puffins and murres (J. Thayer/PRBO unpublished data). It is unknown how much predation affects this rate, versus other factors such as climate change (see below), but these effects could be modeled. Predation at nearshore Castle Rock is unknown. Such natural predation pressure, when combined with other threats, may affect a colony's long-term sustainability.

Climate change is also a threat as it can cause changes to Rhinoceros Auklets' prey base. This can impact breeding attempts and reproductive performance as well as adult survival. The Aņo Nuevo breeding population declined by 20% during the 1998 El Niņo event and did not recover to pre-El Niņo levels until 2001 (PRBO unpublished data). Reproductive performance on Aņo Nuevo was also very low in 1998. Low-frequency (or inter-decadal) climate change may further compound effects of inter-annual events. The population on the Farallon Islands has shown a diminishing reproductive performance from 1986 to 2001, although this trend was not significant (19).


Rhinoceros Auklet chick.

Management and Research Recommendations

  • Determine the health of the population, including population trends, the condition and stability of nesting habitat, the status of prey stocks and fishing activities near colonies, the current predation pressures, and other threats specific to the area.
  • Conduct detailed breeding population surveys on main colonies where current numbers are unknown, Castle Rock and the Farallon Islands. Access to Castle Rock is difficult due to the high density of marine mammals and birds sensitive to disturbance, but late August burrow censuses may be feasible. Southeast Farallon trend information may be obtainable from mark/recapture data, especially in conjunction with the novel use of radar for detecting auklets flying in to the colony.
  • Investigate impacts of habitat changes, such as loss of vegetation and soil erosion at Aņo Nuevo Island and Castle Rock, and restore nesting habitats where feasible.
  • Examine the relationship between Rhinoceros Auklets, forage fish resources, and commercial fisheries to evaluate possible impacts and guide fisheries management.
  • Continue and expand commercial fishery shipboard Observer programs to document mortality of Rhinoceros Auklets in gill nets, and develop methods for preventing further entanglement.
  • Model effects of current and recent oil spills to estimate impacts to Rhinoceros Auklets which are seldom recovered, and model impacts of potential spills to determine appropriate levels of rescue and restoration efforts.

Monitoring Needs
The state's breeding population should be censused periodically (e.g., about every 10 years), preferably during the peak of the incubation period (April and May) or even during the main part of the breeding season (April to July). This is especially important for Rhinoceros Auklet colonies with many perceived threats. For example, populations of surface-nesting or roosting birds or pinnipeds should be monitored at important auklet colonies, such as Castle Rock, which would include assessments of soil erosion caused by these species and its affects on auklet nesting habitat.

References

  1. Gaston, A.J., and S.B.C. Dechesne. 1996. Rhinoceros Auklet (Cerorhinca monocerata). In: The Birds of North America, No. 212 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.

  2. Kondratyev, A.Y., N.M. Litvinenko, Y.V. Shibaev, P.S. Vyatkin, and L.F. Kondratyeva. 2000. The breeding seabirds of the Russian Far East. In: Seabirds of the Russian Far East. Canadian Wildlife Service Special Publication. p.37-81.

  3. Briggs, K. T., Tyler, W. B., Lewis, D. B., and Carlson, D. R. 1987. Bird communities at sea off California: 1975-1983. Studies Avian Biol. 11.

  4. Briggs, K. T., D. H. Varoujean, W. W. Williams, R. G. Ford, M. L. Bonnell, and J. L. Casey. 1992. Seabirds of the Oregon and Washington OCS, 1989-1990. Chapter III in Oregon and Washington Marine Mammal and Seabird Surveys. Final Report to the Pacific OCS Region, Minerals Management Service, U.S. Dept. of the Interior, Los Angeles, CA. 162 pp.

  5. Morgan, K.H., K. Vermeer, and R.W. McKelvey. 1991. Atlas of pelagic birds of western Canada. Canadian Wildlife Service Occasional Paper No.72.

  6. Grinnell, J. 1926. The evidence of the former breeding of the Rhinoceros Auklet in California. Condor 28:37-40.

  7. Sowls, A. L., DeGange, A. R., Nelson, J. W., and Lester, G. S. 1980. Catalog of California seabirdcolonies. U.S. Dept. Interior, Fish & Wildlife Serv., Biol. Serv. Program. FWS/OBS 37/80.

  8. LeValley, R. and J. Evens. 1982. The nesting season: middle Pacific coast region. American Birds 36:1011-1015.

  9. Ainley, D.G., and R.J. Boekelheide. 1990. Seabirds of the Farallon Islands. Stanford University Press: Stanford, CA.

  10. Carter, H.R., G.J. McChesney, D.L. Jaques, C.S. Strong, M.W. Parker, J.E. Takekawa, D.L. Jory, and D.L. Whitworth. 1992. Breeding populations of seabirds in California, 1989-1991. Unpublished Report of theU.S. Fish and Wildlife Service, Dixon, CA.

  11. McChesney, G.J., H.R. Carter, and D.L. Whitworth. 1995. Reoccupation and extension of southern breeding limits of Tufted Puffins and Rhinoceros Auklets in California. Colonial Waterbirds 18:79-90.

  12. Wilson, U.W. 1986. Artificial Rhinoceros Auklet Cerorhinca monocerata burrows: a useful tool for management and research. Journal of Field Ornithology 57:295-299.

  13. Hester, M.M. 1998. Abundance, reproduction and prey of Rhinoceros Auklet, Cerorhinca monocerata, on Aņo Nuevo Island, California. Thesis, Moss Landing Marine Laboratories, San Francisco State University.

  14. Kuroki, M., A. Kato, Y. Watanuki, A. Takahashi. 1998. Artificial nest boxes for the study of breeding ecology of Rhinoceros Auklet Cerorhinca monocerata. J. Yamashina Inst. Ornithol. 30: 40-46.

  15. Gardner, D. A., J. A. Thayer, and W. J. Sydeman. In prep. Site fidelity in Rhinoceros Auklets (Cerorhinca monocerata): temporal and spatial variability in mate and success effects.

  16. Baltz, D.M. and G.V. Morejohn. 1977. Food habits and niche overlap of seabirds wintering on Monterey Bay, California. Auk 94:526-543.

  17. Morejohn, G.V., J.T. Harvey, and L.T. Krasnow. 1978. The importance of Loligo opalescens in the food web of marine vertebrates in Monterey Bay. California Department of Fish and Game Bulletin 169:67-98.

  18. Thayer, J.A., M.M. Hester, and W.J. Sydeman. 2000. Conservation biology of Rhinoceros Auklets,Cerorhinca monocerata, on Aņo Nuevo Island, California, 1993-1999. Endangered Species Update 17: 62-67.

  19. Sydeman, W.J., M.M. Hester, J.A. Thayer, F. Gress, P. Martin, and J. Buffa. 2001. Climate change,reproductive performance and diet composition of marine birds in the Southern California Current System,1969 - 1997. Progress in Oceanography 49:309-329.

  20. Smail, J., Ainley, D.A. & Strong, H. 1972. Notes on birds killed in the 1971 San Fransisco oil spill. California Birds 3:25-32.

  21. Page G.W., H.R. Carter, and R.G. Ford. 1990. Numbers of seabirds killed or debilitated in the 1986 Apex Houston oil spill in central California. Studies in Avian Biology 14: 164-174.

  22. Helm, Roger C, H.R. Carter, and S. Newman. 1997. The 1997 Nakhodka oil spill in Japan: observations on response, seabird injury assessment, and wildlife care. Proc. Int. Conf. Eff. Oil Wildl., No. 5: 167-172. ("Fifth International Conference Effects of Oil on Wildlife, November 3-6, 1997"; Ottum, Nancy D., editor).

  23. Nur, N., W.J. Sydeman, P. Pyle, L.E. Stenzel, D.G. Ainley & T.G. Schuster. 1997. Temporal, spatial,and species-specific patterns of chronic oiling as revealed by the Beached Bird Survey, Farallon Oiled BirdSurvey and bird rescue programs in central California. Report to the California Department of Fish and Game, Office of Oil Spill Prevention and Response (Chapter 1).

  24. Sato, H. 1999. Seabirds affected by the oil pollution in the Japan Sea in January 1986. Journal of theYamashina Institute for Ornithology Nov. 30: 31 (2): 134-141.

  25. Oka, N. and M. Okuyama. 2000. Nutritional status of dead oiled rhinoceros auklets (Cerorhinca monocerata) in the Southern Japan Sea. Marine Pollution Bulletin 40(4): 340-347.

  26. Sydeman, W.J. 1996. Non-profit source pollutants in the Gulf of the Farallones: an evaluation of contaminant levels and bioaccumulation in marine birds, mammals, and their prey. Unpublished report of the Point Reyes Bird Observatory, Stinson Beach, CA.

  27. Forney, K.A., S.R. Benson, and G.A. Cameron. 2001. Central California gillnet effort and bycatch of sensitive species, 1990-1998. University of Alaska Sea Grant College Program Report. Seabird bycatch: Trends, roadblocks, and solutions. University of Alaska Sea Grant College Program, Fairbanks, Alaska
    AK-SG-01-01. p.141-160.

  28. Lewis, D.B. and B. Tyler. 1987. Management recommendations for coastal terrace and island resources at Aņo Nuevo State Reserve. Unpublished Report to California Department of Parks and Recreation, Aņo Nuevo State Reserve. Institute of Marine Sciences, University of California Santa Cruz.

  29. Jaques, D., and C.S. Strong. 2001. Seabird status at Castle Rock National Wildlife Refuge, 1997-1999. Unpublished report, Crescent Coastal Research Exchange, Astoria, OR.

Aņo Nuevo Island Habitat Restoration Project with Oikonos