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Xantus's Murrelet Synthliboramphus hypoleucus

This species is considered Vulnerable because of its small range and small, declining population. Several colonies have gone extinct, and introduced predators are causing declines in some of the remaining nine colonies. Conservation action is beginning to have some positive effects, and the continuing eradication of introduced predators from existing colonies, the discovery of new colonies and/or the recolonisation of former colonies may eventually result in a downlisting to Near Threatened.

Taxonomic source(s)
AOU. 1998. Check-list of North American birds. American Ornithologists' Union, Washington, D.C.
Sibley, C. G.; Monroe, B. L. 1990. Distribution and taxonomy of birds of the world. Yale University Press, New Haven, USA.
Stotz, D. F.; Fitzpatrick, J. W.; Parker, T. A.; Moskovits, D. K. 1996. Neotropical birds: ecology and conservation. University of Chicago Press, Chicago.

Brachyramphus hypoleuca Collar and Andrew (1988), Brachyramphus hypoleuca hypoleuca Collar and Andrew (1988), Brachyramphus hypoleucus Stotz et al. (1996), Brachyramphus hypoleucus hypoleucus Stotz et al. (1996)

24 cm. Small, black-and-white alcid. Black upperparts. White underparts. White underwing linings. Black on head extends to bill. Partial white eye-ring. Shortish, stout bill. Nominate subspecies has more extensive white on face and ear-coverts, forming crescent in front of and over eye. Similar spp. Craveri's Murrelet S. craveri has partial breast- band, black extending under bill and different underwing colour and bill shape. Voice Shrill whistle, sometimes given as series.

Distribution and population
Synthliboramphus hypoleucus breeds off the coast of southern California, USA and Baja California, Mexico. Based on data from aerial and boat surveys between 1975 and 2003, the world population has been estimated at 39,700, of which 17,000 are likely to be breeding in any given year (Karnovsky et al. 2005). In the USA an estimated 885-2,575 breeding pairs occur, the biggest colony on the island of Santa Barbara holds 500-1,250 pairs (B. Keitt and D. Whitworth in litt. 2003). Small numbers breed on Anacapa (200-600 pairs), Santa Cruz (100-300 pairs), San Miguel (50-300 pairs), and San Clemente islands (10-50 pairs), USA (Sowls et al. 1980, Hunt et al. 1981, Carter et al. 1992, Drost and Lewis 1995). Nesting is suspected at Santa Catalina Island (25-75 pairs) (B. Keitt and D. Whitworth in litt. 2003). The Santa Barbara colony has been stable since the 1980s, but recent surveys suggest a decline (B. Keitt and D. Whitworth in litt. 2003). In Mexico, it is known to breed on Los Coronados (750-1,250 pairs), San Jeronimo, San Benito (250-500 pairs), and two islets offshore of Guadalupe Island. Nesting was also recently confirmed on Todos Santos (B. Keitt in litt. 2007), and may also occur on the San Martin islands based on vocalizations heard during the breeding season. There are two distinct subspecies, the southern form breeding on only the three San Benito Islands and two rocks offshore of Guadalupe Island. Other likely former breeding colonies (Cedros, Natividad, Asuncion and San Roque) have been extirpated by invasive animals (B. Keitt and D. Whitworth in litt. 2003). Both subspecies breed sympatrically on the San Benito Islands, and the presence of intermediates suggests that some mixing takes place, although most mating is apparently assortive (Wolf et al. 2006). Post breeding birds disperse north and have been recorded in some number in late summer off British Columbia, Canada (Gaston and Jones 1998).

Population justification
Based on at sea survey data from 1975 to 2003, Karnovsky et al. (2005) were able to estimate a current North American at-sea population of 39,700, of which 17,000 are likely to be mature breeding individuals. Although this estimate is based on extrapolation from survey data, the population estimate is perhaps best placed conservatively at 10,000-19,999 individuals. This equates to 6,667-13,333 mature individuals, rounded here to 6,000-15,000 mature individuals.

Trend justification
A number of colonies have been extirpated by introduced predators and alien invasive species continue to threaten some colonies. A number of other threatening processes are on-going, the combined effects of which are suspected to be causing a moderate decline in this species's global population.

It nests on steep sea-slopes, canyons and cliffs with a sparse cover of herbaceous and shrubby plants (Drost and Lewis 1995). It is a generalist predator, and may exploit higher prey concentrations around pelagic convergence lines (Hamilton et al. 2004). Around Santa Barbara, it feeds on larval fish, especially northern anchovy Engraulis mordax (Hunt and Butler 1980, Hunt et al. 1981). Breeding effort and performance are lower when anchovy abundance is low (Hunt and Butler 1980). Adults enter and leave the nesting colonies at night when there is little or no moon, typically arriving on the Channel Islands in mid-February. Nesting persists through mid-June with peak nesting from late March to late April (Jones et al. 2005). Clutches consist of two eggs laid approximately eight days apart with replacement of lost clutches unusual. Incubation takes c. 34 days (Jones et al. 2005). There are no recent records of them breeding under shrubs on top of Anacapa Island, a habitat used frequently on nearby, rat-free Santa Barbara Island (Jones et al. 2005).

Invasive mammals were responsible for all known and suspected colony extinctions and in 1995 were present on all the larger colonies and former colonies but Santa Barbara Island (McChesney and Tershy 1998). There was heavy cat predation on North Coronado until the mid-1990s (Jehl and Bond 1975, Drost and Lewis 1995). Black rats Rattus rattus almost extirpated the species from Anacapa (Drost and Lewis 1995), but have now been successfully eradicated (Whitworth et al. 2005). The most significant current threat to Xantus's Murrelet recovery is the presence of invasive cats on Guadalupe Island, likely the most important historical site for the southern subspecies (B. Tershy in litt. 2007). Cat predation is thought to have caused the extirpation, or at the very least, significantly reduced the population on the main island of Guadalupe (Keitt et al. 2006). House mice were recently introduced the the Coronados Islands and deer mice Peromyscus maniculatus anacapae (native to nearby Cedros Island) have also been introduced to the San Benito Islands. Deer mice predate eggs on Santa Barbara (Murray et al. 1983), however they were established on Anacapa long before rats were introduced, precluding them from consideration as the cause of declines there (Jones et al. 2006). All Xantus's breeding colonies in California are legally protected as National Parks, private protected areas or military bases. In Mexico, however, only the three southernmost former breeding islands were legally protected, while all current breeding islands were not protected (Wolf et al. 2006). Pollution from offshore oil-wells or the Los Angeles oil-tanker lane could extirpate the species from the south California Bight (Drost and Lewis 1995). Further threats are drowning in drift gill-nets, nest-site disturbance, bright lights used by the squid fishery that cause disturbance and mortality and possibly organochlorine pollution (Drost and Lewis 1995). The 80% decline in zooplankton off southern California from 1951 to 1993 may be detrimental to the species. Changes in sea temperature associated with global climate change could have an impact on food availability in future (S. Wolf in litt. 2007).

Conservation Actions Underway
All potential breeding islands in the USA and Mexico have been surveyed, with the exception of the offshore rocks of Cedros Island (B. Tershy in litt. 1999). Over the past 10 years, most invasive mammals, including cats, rats, goats, sheep, rabbits, donkeys and dogs have been removed from almost all islands that are known current or suspected historical nesting sites in the US and Mexico (McChesney and Tershy 1998, B. Keitt and D. Whitworth in litt. 2003, Whitworth et al. 2005, Keitt 2005, Aguire et al. in press). The most important remaining conservation action is to eradicate cats from Guadalupe Island. Because of its large size and lack of native mammals, Guadalupe may have been the largest Xantus's Murrelet breeding colony and was very likely the most important colony for the southern subspecies. The Xantus's Murrelet is currently listed as Endangered in Mexico and Threatened under the California Endangered Species Act, and is currently a candidate species for federal listing in the USA (S. Wolf in litt. 2007). In 2003, fishing and other extractive uses was banned within important areas of the Channel Islands National Marine Sanctuary in an attempt to reduce light and noise pollution in important near-shore staging areas. However, the exclusion zone covers only a small buffer area around some colonies, and may be ineffective at minimising threats (S. Wolf in litt. 2007). Guadalupe Island has just been declared a Biosphere Reserve (thanks to Conservación de Islas) (B. Tershy in litt. 1999). The remaining Mexican islands with current or former breeding colonies are either in existing biosphere reserves (Natividad, Asunción and San Roque) or in a proposed new biosphere reserve. This is the first step to regulating tourism and the more damaging impact of commercial fishers (B. Tershy in litt. 1999). A pilot habitat restoration for the species has begun on Santa Barbara Island (Wolf 2008). Conservation Actions Proposed
Eradicate introduced predators on other small islands (Drost and Lewis 1995), including ground squirrels from Natividad Island, invasive house mice from Coronados Island and recently introduced deermice from the Western San Benito Island (B. Tershy in litt. 2007). Develop strategies to remove predators from larger islands, with a particular focus on removing cats from Guadalupe Island (B. Tershy in litt. 2007). Develop contingency plans to prevent the establishment of new predator populations (Drost and Lewis 1995). Survey remaining potential breeding islands (Drost and Lewis 1995). Continue to monitor population trends with precision (Drost and Lewis 1995). Regulate tourism on Baja California islands (Drost and Lewis 1995). Assess the impact of gill-net fisheries (Drost and Lewis 1995). Conduct further studies to determine levels of genetic differentiation and the extent of mixing between the two subspecies to clarify their taxonomic status.

Related state of the world's birds case studies

Aguirre-Muñoz, A., Croll, D.A., Donlan, C.J., Hermosillo, H.R.W.M.A., Howald, G.A., Keitt, B.S., Luna-Mendoza, L., Rodríguez-Malagón, M., Salas-Flores, L.M., Samaniego-Herrera, A., Sanchez-Pacheco, J.A., Sheppard, J., Tershy, B.R., Toro-Benito, J., Wolf, 2007. High-impact conservation action: invasive mammal eradication from the islands of western Mexico. Ambio 36.

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

DeLong, R. L.; Crossin, R. S. 1968. Status of seabirds on Islas de Guadalupe, Natividad, Cedros, San Benitos, and Los Coronados.

Drost, C. A.; Lewis, D. B. 1995. Xantus' Murrelet {iSynthliboramphus hypoleucas). In: Poole, A.; Gill, F. (ed.), The birds of North America, No. 164, pp. 1-24. The Academy of Natural Sciences, and The American Ornithologists' Union, Philadelphia, and Washington, DC.

Gaston, A. J.; Jones, I. L. 1998. The Auks. Oxford University Press, Oxford.

Hamilton, C.; Carter, H. R.; Golightly, R. T. 2004. Diet of Xantus's Murrelets in the Southern Californian Bight. Wilson Bulletin 116: 152-157.

Hunt, G. J.; Pitman, R. L.; Naughton, M.; Winnett, K.; Newman, A.; Kelly, P. R.; Briggs, K. T. 1981. Summary of marine mammals and seabird surveys of the southern Californian Bight area, 1975-1978.

Hunt, G. L.; Butler, J. L. 1980. Reproductive ecology of Western Gulls and Xantus' Murrelets with respect to food resources in the southern California Bight. California Cooperative Oceanic Fisheries investigations. Reports 21: 62-67.

Jehl, J. R.; Bond, S. I. 1975. Morphological variation and species limits in murrelets of the genus Endomychura. Transactions of the San Diego Society of Natural History 18: 9-23.

Jones, H.P., Williamhenry III, R., Howald, G.R., Tershy, B.R. and Croll, D.A. 2005. Predation of artificial Xantus’s murrelet (Synthliboramphus hypoleucus scrippsi) nests before and after black rat (Rattus rattus) eradication. Environmental Conservation 32: 320-325.

Karnovsky, N. J.; Spear, L. B.; Carter, H. R.; Ainley, D. G.; Amey, K. D.; Balance, L. T.; Briggs, K. T.; Ford, R. G.; Hunt, G. L. Jr.; Keiper, C.; Mason, J. W.; Morgan, K. H.; Pitman, R. L; Tynan, C. T. 2005. At sea distribution, abundance and habitat affinities of Xantus’s Murrelets. Marine Ornithology 33(2): 89-104.

Keitt, B. 2005. Status of Xantus's Murrelet and its nesting habitat in Baja California. Marine Ornithology 33: 105-114.

Keitt, B. S.; Henry, R. W.; Aguirre, A.; Garcia, C.; Mendoza, L. L.; Hermosillo, M. A.; Tershy, B.; Croll, D. 2006. Impacts of introduced cats (Felis catus) on the Guadalupe island ecosystem. In: Prado, G. K. S., Peters, E. (ed.), Taller sobre la restauración y conservación de Isla Guadalupe: memorias., pp. 10. Instituto Nacional de Ecología, Mexico City.

McChesney, G. J.; Tershy, B. R. 1998. History and status of introduced mammals and impacts to breeding seabirds on the California channel and northwestern Baja California islands. Colonial Waterbirds 21: 335-347.

Murray, K. G.; Winnett-Murray, K.; Hunt, G. J.; Schwartz, D. B. 1983. Breeding biology of the Xantus' Murrelet. Condor 85: 12-21.

Sowls, A. L.; DeGange, A. R.; Nelson, J. W.; Lester, G. S. 1980. Catalogue of California seabird colonies. US Fish and Wildlife Service, US Department of the Interior, Washington, D.C.

Whitworth, D. L.; Carter, H. R.; Young, R. J.; Koepke, J. S.; Gress, F.; Fangman, S. 2005. Initial recovery of Xantus’s Murrelets following rat eradication on Anacapa Island, California. Marine Ornithology 33: 131-137.

Wolf, S. 2008. Xantus's Murrelet Technical Committee. Pacific Seabirds 35(1): 17-18.

Wolf, S.; Phillips, C.; Zepeda-Dominguez, J. A.; Albores-Barajas, Y.; Martin, P. 2005. Breeding biology of Xantus’s Murrelets at the San Benito Islands, Baja California, Mexico. Marine Ornithology 33: 123-129.

Further web sources of information
Audubon WatchList

Text account compilers
Benstead, P., Bird, J., Butchart, S., Calvert, R., Capper, D., Gilroy, J., Harding, M., Sharpe, C J, Anderson, O.

Keitt, B., Tershy, B., Whitworth, D., Wolf, S.

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

Recommended citation
BirdLife International (2014) Species factsheet: Synthliboramphus hypoleucus. Downloaded from on 17/04/2014. Recommended citation for factsheets for more than one species: BirdLife International (2014) IUCN Red List for birds. Downloaded from on 17/04/2014.

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.

Additional resources for this species

ARKive species - Xantus’s murrelet (Synthliboramphus hypoleucus) 0

Key facts
Current IUCN Red List category Vulnerable
Family Alcidae (Auks)
Species name author X
Population size 6000-15000 mature individuals
Population trend Decreasing
Distribution size (breeding/resident) 300 km2
Country endemic? No
Links to further information
- Additional Information on this species