Larus heermanni

Whilst not overpoweringly large, Heermann's gull frequently harasses other seabirds into relinquishing their catch, picking mainly on the brown pelican (Pelecanus occidentalis) and the California sea lion (Zalophus californianus). It takes small fish from the water surface and sometimes dives to chase fish. It also scavenges and feeds opportunistically on lizards, insects, invertebrates and herring gull eggs along beaches, estuaries and marshes (2) (3). Heermann's gull prefers to forage alone or in small groups, but during the breeding season it forms large colonies on the ground. Up to 100 pairs construct nests out of twigs and stones between rocks, lining the nest with feathers or shells. The female lays one to three spotted eggs in late April, which are incubated by both parents for 28 days. They hatch between mid and late May and the hatchlings are fed by the male and the female until they fledge 45 days later. If food is scarce, parents may choose one chick to feed, starving the other or even pecking it to death. Chicks that survive until adulthood begin to breed at three or four years of age (2) (3).

Heermann's gull is distinctive with a dark grey-brown back and wings, pale grey underside and rump, and white head, tips to the tail and wing feathers. The bill is bright red and sometimes tipped with black. The legs are black. Non-breeding adults have grey or brown streaks on the head and immature birds are dark brown all over, with a pale base to the red bill (2).

Coastal w Mexico; winters British Columbia to Guatemala.

East North Pacific

Larus heermanni has a population of 525,000 individuals⁹, 90% of which nest on Isla Rasa, Mexico². There are 150 pairs on George Island, 1,500 on Cholluda², 4,000 on Cardonosa and 200 on San Il de Fonso⁸, with breeding south to Nayarit and islas San Benito and San Roque, and sporadically north to California, USA^2,3. Post-breeding dispersal occurs commonly to central California, USA, and in smaller numbers north to British Columbia, Canada, and south to Guatemala². 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 1975².

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Transient

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Non-breeding

Global Range: (20,000-2,500,000 square km (about 8000-1,000,000 square miles)) BREEDING: mainly on islets off Pacific coast of Baja California, in Gulf of California, and locally off the coast of Mexico south to Sinaloa and Nayarit. Isolated breeding in coastal California (AOU 1998). NON-BREEDING: from breeding grounds north to southern British Columbia, common in California; south to Pacific coast of Guatemala (AOU 1998).

Heermann's gull breeds off the coast of Mexico and in the Gulf of California, particularly on Isla Rasa, where the population has a stronghold. Very occasionally it is seen breeding in San Francisco Bay (2). Non-breeders spend the breeding season at the wintering sites along the coasts of California and British Colombia (3).

Length: 48 cm

Weight: 500 grams

Habitat and Ecology

Systems

• Terrestrial
• Marine

Depth range based on 3048 specimens in 1 taxon.
Water temperature and chemistry ranges based on 188 samples.

Environmental ranges
  Depth range (m): 0 - 0
  Temperature range (°C): 12.220 - 16.430
  Nitrate (umol/L): 0.204 - 3.951
  Salinity (PPS): 30.381 - 33.496
  Oxygen (ml/l): 5.646 - 6.395
  Phosphate (umol/l): 0.330 - 0.674
  Silicate (umol/l): 1.436 - 16.169

Graphical representation

Temperature range (°C): 12.220 - 16.430

Nitrate (umol/L): 0.204 - 3.951

Salinity (PPS): 30.381 - 33.496

Oxygen (ml/l): 5.646 - 6.395

Phosphate (umol/l): 0.330 - 0.674

Silicate (umol/l): 1.436 - 16.169
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

Comments: BREEDING: Nests on flat rocky islands or isolated coasts, often with scattered grass clumps present. Nests on ground between rocks or near grass clumps. The nest is constructed of sticks and surrounding vegetation. NON-BREEDING: seacoasts, beaches, bays and estuaries (AOU 1983).

This coastal gull prefers beaches, rocky shores, estuaries and lagoons for foraging and breeding, and will often nest on offshore islands. During the winter it moves out to sea or remains in remote coastal areas (2) (3).

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

Post-breeding migrants move up the Pacific coast as far north as southern British Columbia; early migrants appear in May in British Columbia and numbers peak in mid-October, after which numbers decline rapidly as birds move south (Campbell et al. 1990).

Comments: Eats marine fishes, crustaceans, and mollusks. May pirate fish from pelicans and cormorants; also scavenges for food along beaches and shores.

Lays two to three eggs April-June (Terres 1980). Usually only two young produced from three-egg clutches.

The following is a representative barcode sequence, the centroid of all available sequences for this species.

There are 3 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 3
Specimens with Barcodes: 3
Species With Barcodes: 1

Year Assessed

Assessor/s

Reviewer/s

Contributor/s

Justification

History

• 2008
  Near Threatened
• 2006
  Near Threatened
• 2004
  Near Threatened

Canada

Rounded National Status Rank: NNA - Not Applicable

United States

Rounded National Status Rank: N4N - Apparently Secure

Rounded Global Status Rank: G4 - Apparently Secure

Classified as Near Threatened (NT) on the IUCN Red List 2006 (1).

Population

Population Trend

Major Threats

Concentrated into just eight colonies within a small area, Heermann's gull is considered to be stable, but faces risks inherent in such a compact community. Ninety percent of the world's population is found on Isla Rasa in the Gulf of California so conservation of this island habitat is crucial to the survival of this species. It is estimated that there are 150,000 pairs of Heermann's gulls living today, and that their main threat is the increasing population of the yellow-footed gull (Larus livens) which is a predator of Heermann's gull eggs and chicks (2).

Conservation Actions

Very little specific conservation action is targeted at Heermann's gull because although its range is small and it is therefore vulnerable, the population is judged to be stable. It has proved extremely difficult to survey, producing wildly different population figures for each census. However, it is important to keep some idea of the population size in order to ensure that the yellow-footed gull is not impacting negatively on Heermann's gull (2). Ilsa Rasa became a sanctuary in 1964 (3).