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Larus heermanni

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA AVES CHARADRIIFORMES LARIDAE

Scientific Name: Larus heermanni
Species Authority: Cassin, 1852
Common Name/s:
English – Heermann's Gull

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2012
Assessor/s: BirdLife International
Reviewer/s: Butchart, S. & Symes, A.
Contributor/s: Keitt, B., Tershy, B. & Velarde, E.
Justification:
This species is considered Near Threatened as it has a highly restricted breeding range, with 90% of the world population breeding on a single small island. Populations fluctuate widely in response to climatic events, although these fluctuations are less than one order of magnitude. It is likely to be at high risk from catastrophic events or local anthropogenic changes, and should be carefully monitored.

History:
2010 – Near Threatened
2008 – Near Threatened
2006 – Near Threatened
2004 – Near Threatened

Geographic Range [top]

Range Description: Larus heermanni has a population of 525,000 individuals (Kushlan et al. 2002), 90% of which nest on Isla Rasa, Mexico (Burger and Gochfeld 1996). There are 150 pairs on George Island, 1,500 on Cholluda (Burger and Gochfeld 1996), 4,000 on Cardonosa and 200 on San Il de Fonso (E. Velarde in litt. 1998), with breeding south to Nayarit and islas San Benito and San Roque, and sporadically north to California, USA (Everett and Anderson 1991, Burger and Gochfeld 1996). Post-breeding dispersal occurs commonly to central California, USA, and in smaller numbers north to British Columbia, Canada, and south to Guatemala (Burger and Gochfeld 1996). Numbers on Isla Rasa are similar to estimates in the late 1960s, but there have been significant fluctuations with a low of 55,000 pairs in 1975 (Burger and Gochfeld 1996).

Countries:
Native:
Canada; Mexico; United States
Vagrant:
Costa Rica; Guatemala
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Kushlan et al. (2002)

Population Trend: Increasing

Habitat and Ecology [top]

Habitat and Ecology: This coastal species breeds very synchronously and often at high densities (up to 110 nests/100m2) on remote rocky coasts and islets (Velarde 1992, 1999). It feeds largely within inshore waters and in the littoral zone.

Systems: Terrestrial; Marine

Threats [top]

Major Threat(s): Population fluctuations are probably caused by the effects of El Niño Southern Oscillation (compounded by over-fishing) on prey abundance and consequently breeding success, and even adult survival (Velarde et al. 1994, E. Velarde in litt. 1998, Velarde 1999). However, fluctuations are considerably less than one order of magnitude and therefore the species is not even close to qualifying as threatened for this reason. The occupied breeding range is very small, but Isla Rasa was declared a sanctuary in 1964 (Anderson et al. 1976), and is currently very well-managed during the breeding season by resident biologists, who discourage egg-collecting and disturbance (E. Velarde in litt. 1998, B. Tershy and B. Keitt in litt. 1999).

Conservation Actions [top]

Conservation Actions: Conservation Actions Underway
Conservation Actions Proposed
Continue to take active measures to protect breeding populations on islands, particularly Isla Rasa. Monitor population trends at breeding sites, particularly in response to climatic change or fluctuation.

Citation: BirdLife International 2012. Larus heermanni. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 19 May 2013.
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