Archived 2014 discussion: Xantus’s Murrelet (Synthliboramphus hypoleucus) is being split: list S. hypoleucus as Endangered and S. scrippsi as Vulnerable?

The initial deadline for comments on this topic is 28 April 2014, and therefore later than for most other topics currently under discussion.

This is part of a consultation on the Red List implications of extensive changes to BirdLife’s taxonomy for non-passerines

Lynx Edicions and BirdLife International will soon publish the HBW-BirdLife Illustrated Checklist of the Birds of the World, building off the Handbook of the Birds of the World series, and BirdLife’s annually updated taxonomic checklist.

The new Checklist will be based on the application of criteria for recognising species limits described by Tobias et al. (2010). Full details of the specific scores and the basis of these for each new taxonomic revision will be provided in the Checklist.

Following publication, an open and transparent mechanism will be established to allow people to comment on the taxonomic revisions or suggest new ones, and provide new information of relevance in order to inform regular updates. We are also actively seeking input via a discussion topic here regarding some potential taxonomic revisions that currently lack sufficient information.

The new Checklist will form the taxonomic basis of BirdLife’s assessments of the status of the world’s birds for the IUCN Red List. The taxonomic changes that will appear in volume 1 of the checklist (for non-passerines) will begin to be incorporated into the 2014 Red List update, with the remainder, and those for passerines (which will appear in volume 2 of the checklist), to be incorporated into subsequent Red List updates.

Preliminary Red List assessments have been carried out for the newly split or lumped taxa. We are now requesting comments and feedback on these preliminary assessments.

Xantus’s Murrelet Synthliboramphus hypoleucus is being split into S. hypoleucus and S. scrippsi, following the application of criteria set out by Tobias et al. (2010), and consideration of genetic evidence (Birt et al. 2012).

Prior to this taxonomic change, S. hypoleucus (BirdLife species factsheet) was listed as Vulnerable under criteria B1ab(iv,v)+2ab(iv,v), on the basis of its small range and small, declining population, with several colonies having gone extinct, and introduced predators causing declines in some of the remaining colonies.

Numbers are likely to have declined extensively at many colonies in the late 19th and early 20th centuries because of several factors, especially introduced predators (particularly cats Felis catus and Black Rats Rattus rattus), loss and alteration of breeding habitats (because of ranching and introduced plants for example, which may have led to enhanced predation by natural predators, particularly Deer Mice Peromyscus maniculatus and Barn Owls Tyto alba), and factors at sea (e.g. oil pollution, lights, possible prey changes) (reviewed by Birt et al. 2012).

Based on at-sea survey data from 1975 to 2003, Karnovsky et al. (2005) were able to estimate a North American at-sea population of 39,700 individuals of the pre-split species, of which 17,000 were thought likely to be mature breeding individuals. Although this estimate is based on extrapolation from survey data, the population estimate was placed conservatively at 10,000-19,999 individuals. This equates to 6,667-13,333 mature individuals, rounded to 6,000-15,000 mature individuals in the previous assessment.

S. scrippsi breeds on islands off southern California (San Miguel, Santa Cruz, Anacapa, Santa Barbara, San Clemente, and, formerly, Santa Catalina) and western Baja California (San Benito, and the Coronado and San Jerónimo islands) (Chesser et al. 2012). On large islands the species is confined largely or entirely to offshore rocks (Drost and Lewis 1995). Breeding on San Martín and Cedros islands, Baja California, is uncertain (Chesser et al. 2012). The species winters offshore from northern California (rarely) south to southern Baja California (Chesser et al. 2012).

This species’s Area of Occupancy (AOO) when breeding is estimated at only 62 km2, thus potentially meeting the thresholds for Endangered under criterion B2; however, it is thought to breed at more than five locations. Information is requested on the number of breeding locations occupied by this species, where locations are defined by the most important threat to the species, in this case presumed to be introduced species, thus the number of locations is likely to equal the number of islands and islets occupied by breeding birds. If this number is thought to be 10 or fewer, the species is likely to qualify as Vulnerable. If this number is thought to exceed 10 but remain fewer than 20, the species would likely qualify as Near Threatened under the B2 criterion.

Additional information is sought on whether the species could qualify as Near Threatened or Vulnerable under criterion A, based on its likely rate of decline over 36 years (estimate of three generations) into the past or future. Species listed as Near Threatened under criterion A are typically thought to be declining by 25-29% over three generations, while those listed as Vulnerable are thought to be declining by 30-49%. Information is also invited on the likely population size of S. scrippsi, and whether it could number fewer than 10,000 mature individuals.

S. hypoleucus (as defined following the taxonomic change) breeds on the three San Benito Islands, Guadalupe Island and at least two associated offshore rocks (Birt et al. 2012, Chesser et al. 2012, BirdLife species factsheet). 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), which is considered the most important historical site for S. hypoleucus (B. Tershy in litt. 2007).

Other likely former breeding colonies (Cedros, Natividad, Asuncion and San Roque) are thought to have been extirpated by invasive animals (B. Keitt and D. Whitworth in litt. 2003). Breeding is unconfirmed on San Martín Island, Baja California, and San Clemente and Santa Barbara islands, California (Chesser et al. 2012). The species winters offshore, with presumably the majority of the population remaining in the vicinity of the breeding range along the western coast of Baja California (Chesser et al. 2012).

Information is requested on the number of breeding locations occupied by this species, where locations are defined by the most important threat, in this case presumed to be introduced species, thus the number of locations in this case may equal the number of islands and islets on which the species breeds. If the number of locations is five or fewer, the species would likely be eligible for listing as Endangered under criterion B2, also on the basis that its AOO is estimated at 335 km2 (including Guadalupe Island).

If the species is thought to breed at 6-10 locations, it is nevertheless likely to be listed as Vulnerable under criteria B2; C2a(ii), on the basis of the estimated AOO, and because it is estimated to number fewer than 5,000 breeding birds (Birt et al. 2012) (thus fewer than 10,000 mature individuals), presumed to form one sub-population, and inferred to be in decline.

Comments are invited on these assessments and further information would be welcomed.


Birt, T. P., Carter, H. R., Whitworth, D. L., McDonald, A., Newman, S. H., Gress, F., Palacios, E., Koepke, J. S. and Friesen, V. L. (2012) Rangewide population genetic structure of Xantus’s Murrelet (Synthliboramphus hypoleucus). Auk 129(1): 44–55.

Chesser, R. T. et al. (2012) Fifty-third supplement to the American Ornithologists’ Union Checklist of North American Birds. Auk 129(3): 573–588.

Drost, C. A. and Lewis, D. B. (1995) Xantus’ Murrelet (Synthliboramphus hypoleucus). In: Poole, A. and Gill, F. (Eds.) The Birds of North America, no. 164. Washington D.C. and Philadelphia: Academy of Natural Sciences and American Ornithologists’ Union.

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 and Tynan, C. T. (2005) At sea distribution, abundance and habitat affinities of Xantus’s Murrelets. Marine Ornithology 33(2): 89–104.

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

Tobias, J. A., Seddon, N., Spottiswoode, C. N., Pilgrim, J. D., Fishpool, L. D. C. and Collar, N. J. (2010) Quantitative criteria for species delimitation. Ibis 152: 724–746.

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2 Responses to Archived 2014 discussion: Xantus’s Murrelet (Synthliboramphus hypoleucus) is being split: list S. hypoleucus as Endangered and S. scrippsi as Vulnerable?

  1. Andy Symes says:

    Preliminary proposals

    Based on available information, our preliminary proposals for the 2014 Red List would be to treat:

    S. hypoleucus as Endangered under criterion B2ab(iv,v)

    S. scrippsi as Vulnerable under criterion B2ab(iv,v).

    There is now a period for further comments until the final deadline of 14 May, after which recommended categorisations will be put forward to IUCN.

    The final Red List categories will be published on the BirdLife and IUCN websites in mid-2014, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  2. Andy Symes says:

    Recommended categorisations to be put forward to IUCN

    Following further review, there have been no changes to our preliminary proposals for the 2014 Red List status of these species.

    The final categorisations will be published in mid-2014, following further checking of information relevant to the assessments by BirdLife and IUCN.

Comments are closed.