Volume 49, No. 1

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The rarest alcid: status and history of the Guadalupe Murrelet Synthliboramphus hypoleucus at Isla Guadalupe, Mexico (1892-2007)


1California Institute of Environmental Studies, P.O. Box 1185, Davis, California 95617, USA
2Carter Biological Consulting, 1015 Hampshire Road, Victoria, British Columbia V8S 4S8, Canada
3Current Address: Centro de Investigación Científica y Educación Superior de Ensenada, Unidad La Paz, Miraflores 334 Col. Bellavista, La Paz, Baja California Sur 23050, México
4Current Address: Samara Restoration, 3396 Antoinette Court, Arcata, California 95521, USA
5Current Address: US Fish and Wildlife Service, Arcata Fish and Wildlife Office, 1655 Heindon Road, Arcata, California 95521, USA
6Current Address: California Department of Transportation, 1656 Union Street, Eureka, California 95501, USA
7US Fish and Wildlife Service, San Francisco Bay National Wildlife Refuge Complex, 1 Marshlands Road, Fremont, California 94555, USA


WHITWORTH, D.L., CARTER, H.R., PALACIOS, E., KOEPKE, J.S., MCIVER, W.R., HAMILTON, C.D., MCCHESNEY, G.J. & GRESS, F. 2021. The rarest alcid: status and history of the Guadalupe Murrelet Synthliboramphus hypoleucus at Isla Guadalupe, Mexico (1892-2007). Marine Ornithology 49: 133 - 143

Received 05 November 2020, accepted 16 January 2021

Date Published: 2021/04/15
Date Online: 2021/04/10
Key words: Isla Guadalupe, Islote Morro Prieto, Islote Zapato, Baja California, Guadalupe Murrelet, spotlight surveys, Synthliboramphus hypoleucus


The Guadalupe Murrelet (GUMU) Synthliboramphus hypoleucus is the rarest alcid in the world (< 5 000 pairs), with regular breeding documented only at Islas Guadalupe (hereafter, “Guadalupe”) and San Benito off the west-central coast of Baja California, Mexico. GUMU were discovered at Guadalupe in 1892, but by then feral cats Felis catus had already devastated the population and limited most nesting to predator-free islets just offshore. Despite its status as the only major GUMU breeding island, the population at Guadalupe was never adequately surveyed during the 20th century. In March-April 2007, we used survey techniques developed specifically for Synthliboramphus murrelets to assess the status and distribution of GUMU at Guadalupe. We counted 1 511 GUMU during spotlight surveys in waters around the island. GUMU were abundant near the islets, but also relatively numerous near suitable breeding habitats off the north and south coasts of Guadalupe proper. Searches on four islets yielded 93 nests, most at Islotes Zapato (66; 71%) and Morro Prieto (21; 23%), where scores of abandoned eggs indicated intense competition for nests. We found seven nests on Guadalupe proper, the first proof of breeding there since 1950, but we also found 68 carcasses that confirmed significant predation by cats and raptors. A spotlight survey correction factor yielded 2 418 breeding pairs (95% confidence interval = 1 662-4 367) at Guadalupe and its islets, which accounted for ~90% of the world breeding population (1 822-4 789 pairs). About 1 150-1 750 pairs were estimated on Islotes Zapato and Morro Prieto in 1968, but comparable data were lacking to assess historical or recent changes in population size. Basic studies of GUMU biology have only recently been initiated and should be a continuing priority. Recent conservation actions have benefited the native biota of Guadalupe, but further measures, such as localized rodent control and robust biosecurity on the islets, should be considered to mitigate serious threats to the vulnerable GUMU population and other seabirds.


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