BC Conservation Data Centre: Conservation Status Report
Larus heermanni
Heermann's Gull
| Scientific Name: | Larus heermanni |
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| English Name: | Heermann's Gull |
| Provincial Status Summary | |
| Status: | S4M |
| Date Status Assigned: | April 11, 2025 |
| Date Last Reviewed: | April 11, 2025 |
| Reasons: | This species is a regular migrant that moves north from their breeding areas that are mostly in the Gulf of California. The population in BC has an apparently increasing distributional range and length of stay. Population trends are difficult to determine for the province, but generally indicate increases in both long-term and short-term trend. |
| Range | |
| Range Extent: | F = 20,000-200,000 square km |
| Range Extent Estimate (km2): | 152,120 square km |
| Range Extent Comments: | Campbell et al. (2006b) consider this a very common to abundant late summer and autumn visitor off southern Vancouver Island, common to very common along the west coast of Vancouver Island, north to the vicinity of Tofino, uncommon in the Greater Vancouver area, rare in the Strait of Georgia, and casual elsewhere along the south coast in all seasons. Campbell et al. (2006b) noted that the species is expanding its range and length of stay in British Columbia. That trend has continued and it is now frequent in the Strait of Georgia and records along the coast have increased on both sides of Vancouver Island. The species is now sparsely distributed along the mid and north coasts right into Alaska as far north as the Kenai Peninsula (eBird, accessed March 2024). This species was not reported on pelagic surveys by Morgan et al. (1991) or Kenyon et al. (2009), however it is noted as occurring on offshore banks such as Constance, Swiftsure and La Perouse banks (Campbell et al. 1990b, Campbell et al 2006b, and eBird [accessed March 2024]). The species does not breed in British Columbia and is found breeding on a dozen islands in the Gulf of California (Mellink 2001, Islam and Velarde 2020) and a precarious breeding colony near Seaside, California. After breeding, some of this species disperses along the Pacific coast from Guatemala and north (rarely) to Alaska including a portion that spends the late summer and early fall in British Columbia. Populations in British Columbia fluctuate from year to year with breeding successes in Mexico and California and variation in food abundance (Campbell et al 2006b). Range extent based on records in Campbell et al. 2006 and eBird (accessed March 2024) is 152,120 square km. Very small numbers of birds overwinter in British Columbia. |
| Area of Occupancy (km2): | U = Unknown |
| Occurrences & Population | |
| Number of Occurrences: | Rank Factor not assessed |
| Number of Occurrences with Good Viability / Ecological Integrity: | Rank Factor not assessed |
| Number of Occurrences Appropriately Protected & Managed: | Rank Factor not assessed |
| Population Size: | E = 2,500 - 10,000 individuals |
| Comments: | Campbell et al. (2006b) estimate the BC population at 1500 to 3000 noting that the population fluctuates from year to year. Since the time of that estimate the number of birds in BC appears to have increased. |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | Rank Factor not assessed |
| Comments: | Threats for this species have been summarized from Islam and Velarde (2020). Historically, Heermann's Gull eggs were harvested with an estimated 50,000 eggs removed during one breeding season at Isla Rasa, the main breeding colony for the species in the Gulf of California. Other threats have included high levels of pesticide contaminants in body tissues that were accumulated through diet (the 1980s), direct competition with humans for Pacific Sardine, human disturbance at breeding colonies and predation of eggs and chicks by non-native vertebrates such as black rat (Rattus rattus) and house mouse (Mus musculus). However, more recent studies have detected lower levels of pesticides in body tissues, and nonnative rodents were eradicated from Isla Rasa in 1995. With the establishment of Isla Rasa as a seabird sanctuary by the Mexican Government in 1964, there has been an increase from an estimated low of 55,000 pairs in 1975, to the current global population estimated at 350,000 individuals. This increase may account for recent nesting along the California coastline and an increase in extralimital records in North America in recent decades including the expanding range and length of stay in British Columbia (Campbell et at. 2006). Velarde (1999) noted an impact of predation by Yellow-footed Gulls (Larus livens). |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | GH = Relatively Stable to increase of <25% |
| Comments: | Generation time for this species has been calculated as 8.91 years (Bird et al. 2020) and thus the 3 generation time frame for short-term trends would be 26.74 years. Campbell et al. (2006b) document an increasing distributional range and length of stay (arriving earlier and staying later) in British Columbia and this trend has continued (eBird, accessed March 2024). Population trends for the province are difficult to determine. BC Coastal Waterbird Survey data seem to indicate a relatively stable or increasing trend, though the species range in the province is not fully sampled by this survey (SOCB 2024). Fink et al. (2022) show a decreasing trend in abundance along the Pacific Coast during the 2012 to 2022 time period. Due to the limited breeding range, fluctuations in populations are expected based on breeding successes in the Mexican and California breeding colonies. Maximum reported flock size in the province has also increased from 600 in 1980 (Campbell et al. 1990b) to 1,112 in 1983 (Campbell et al. 2006b) to 2,000 in the year 2000 (eBird, accessed March 2024). |
| Long-Term Trend: | I = Increase of >25% |
| Comments: | The species range in British Columbia has greatly expanded since the publication of the Birds of British Columbia (Campbell et al. 1990b) with birds now found all along the length of the British Columbia coast, although records are sparse north of Vancouver Island (Fink et al. 2022, eBird accessed March 2024). |
| Other Factors | |
| Intrinsic Vulnerability: | B=Moderately vulnerable |
| Comments: | Almost the entire global population breeds on one island, where breeding success is dependent on local food availability (Islam and Velarde 2020). |
| Environmental Specificity: | D=Broad. Generalist or community with all key requirements common. |
| Comments: | Typically found in marine and rocky shoreline areas. |
| Other Rank Considerations: | |
| Information Gaps | |
| Research Needs: | |
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| Stewardship | |
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| Version | |
| Author: | Fraser, D.F. (2024) |
| Date: | March 02, 2024 |
| References | |
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Bird, J., R. Martin, H.R. Akçakaya, et al. 2020. Generation lengths of the world?s birds and their implications for extinction risk. Conservation Biology 34:1252?1261.
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Campbell , R.W. , M.I. Preston , S.G. Sealy, et al.. 2006b. Featured Species ? Heerman?s Gull. Wildlife Afield. 3:152-204.
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Campbell, R.W., N.K. Dawe, I. McTaggart-Cowan, et al. 1990b. The Birds of British Columbia Vol. 2: Nonpasserines: Diurnal Birds of Prey through Woodpeckers. Royal British Columbia Museum, Victoria, BC.
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eBird. ND. eBird: an online database of bird distribution and abundance [web application]. eBird, Cornell Lab of Ornithology, Ithaca, N.Y.
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Fink, D., T. Auer, A. Johnston, et al. 2023. eBird Status and Trends, Data Version: 2022; Released: 2023. Cornell Lab of Ornithology, Ithaca, New York.
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Islam, K. and E. Velarde. 2020. Heermann's Gull (Larus heermanni), version 2.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA.
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Mellink, E. 2001. History and Status of Colonies of Heermann?s Gull in Mexico. Waterbirds: The International Journal of Waterbird Biology 24(2): 188?194.
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Morgan, K.H., K. Vermeer and R.W. McKelvey. 1991. Atlas of Pelagic Birds of Western Canada. Canadian WIldlife Service. Occasional Paper no. 72. 72 pp
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Velarde, E. 1999. Breeding Biology of Heermann's Gulls on Isla Rasa, Gulf of California, Mexico. The Auk 116: 513?519.
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Please visit the website Conservation Status Ranks for information on how the CDC determines conservation status ranks. For global conservation status reports and ranks, please visit the NatureServe website http://www.natureserve.org/.
Suggested Citation:
B.C. Conservation Data Centre. 2024. Conservation Status Report: Larus heermanni. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Oct 3, 2026).