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Larus heermanni Cassin, 1852
Heermann's Gull; Heermann’s Gull
Family: Laridae

Species account author: Jamie Fenneman
Introduction to the Birds

Photograph

© Tim Zurowski     (Photo ID #7963)

Map


Distribution of Larus heermanni in British Columbia.
(Click on the map to view a larger version.)
Source: Distribution map provided by Jamie Fenneman for E-Fauna BC

Species Information

Breeding adult
This plumage is acquired in late winter or early spring (December-February) and is held until late summer (August). The back, scapulars, and upperwing coverts are slate-grey, contrasting with the paler grey rump and uppertail coverts. The flight feathers are blackish with a narrow white trailing edge along the tertials, secondaries, and inner primaries that breaks into tiny white tips to the outer primaries in fresh plumage. The tail is black with a white terminal band. The underparts are wholly grey (paler than the upperparts). The underwing is similarly grey, darker on the flight feathers, and shows a white trailing edge similar to that shown on the upperwing. The head is white, diffusely contrasting with the grey neck (similar in colour to the underparts). The iris is dark, the orbital ring is red, the bill is bright red with a black tip, and the legs and feet are blackish.

Non-breeding adult
This plumage is acquired in the late summer (August) and is held until the late winter (December-February); most birds observed in B.C. are in this plumage. It is similar to the breeding plumage, but the head is extensively streaked and mottled with dusky-grey (darkest on the ear coverts and sides of the face). The eye shows narrow white crescents above and below, contrasting with the otherwise dusky-mottled head.

Second-year immature
This plumage is acquired in the late summer or fall of the second year (~August/ September) and is held throughout the second winter. Second-year immatures are wholly dark sooty-grey (lacking the brown tones found in younger birds), darkest on the head, neck, flight feathers, and tail. A narrow white trailing edge to the wing appears in this plumage, as does a narrow white terminal band on the tail. The bill becomes red (similar to the adult, but duller), and there is usually the suggestion of very narrow pale crescents around the eye. The orbital ring remains dark grey through this plumage.

Juvenile / first-year immature
Juvenal plumage is acquired upon leaving the nest, but is gradually lost over the first winter by a prolonged molt between July and March; a first-summer plumage is acquired by the following spring and is held until the late summer or fall. Fresh juveniles are entirely dark blackish-brown, darkest and blackest on the head, neck, flight feathers, and tail, with extensive buffy-brown feather edges on the upperparts, upperwing coverts, and tertials and fine buff fringes on the feathers of the underparts. The bill is flesh-coloured with an irregular blackish tip (extending towards the base of the bill along the cutting edge) and the orbital ring is dark grey, but bare part colouration is otherwise similar to the adult. By the fall and winter, the feathers of the upperparts and underparts become uniformly dark and lose the buffy feather edges and fringes. Birds at this age (between October and May) thus appear almost uniformly dark brown. By the following summer, the plumage appears worn and somewhat faded (browner), and some dark grey-brown feathers begin to appear on the upperparts and upperwing coverts. The bill may start to become tinged with reddish by this age as well.

Measurements
Total Length: 47-48 cm
Mass: 370-640 g

Source: Sibley (2000); Islam (2002)


Biology

Identification

The identification of adults is straightforward due to a combination of the bright red bill, overall dark grey plumage, white-tipped black tail, and dark legs. Breeding-plumaged birds, with their white head, are particularly distinctive and unlikely to be confused with any other gull or seabird. Juvenile and immature birds, however, may cause some identification problems as their wholly dark brown or sooty plumage may recall several other species.

Immature Heermann’s Gulls is most likely to be confused with a dark-morph jaeger, particularly Pomarine Jaeger or Parasitic Jaeger. This is due both to a similarity in shape, size, and plumage as well as the tendency for Heermann’s Gulls to engage in piracy or kleptoparasitism in a manner that is more commonly associated with the jaegers. Adult jaegers will generally be easily distinguished by the presence of tail streamers, although these can be broken or missing and are not always reliable. In addition, all jaegers (adults and immatures) show a variable white flash in the primaries, visible both from above and (especially) from below. Heermann’s Gulls always show entirely dark wings with, at most, a narrow white trailing edge in older plumages. Despite the superficial similarities, immature Heermann’s Gulls are usually readily distinguishable from jaegers given reasonable views and shouldn’t cause more than momentary confusion in most circumstances.
Vocalizations

The vocalizations of this species are described as low, hollow, and trumpeting calls. These calls include a nasal yoww, a short yek, a high-pitched, whining whee-ee, and a repeated ye ye ye ye.

Source: Sibley (2000); Islam (2002)

Bird calls (and videos) from Cornell's Lab of Ornithology
Breeding Ecology

This species is a post-breeding visitor to B.C. and does not breed in the province.
Foraging Ecology

This species forages solely in the marine environment, both in offshore and nearshore habitats, particularly where tidal rips, surge channels, or areas of upwelling bring abundant nutrients to the surface and concentrate prey. It commonly forages in small to medium-sized (occasionally large) flocks, usually associated with large numbers of California Gulls. It feeds primarily on small schooling fish (herring, sandlance, smelt), crustaceans (shrimp, amphipods, etc.), squid, and other marine invertebrates, but is an opportunistic feeder and will consume whatever is available. It often scavenges along the shoreline for carrion and other refuse but, unlike most other gull species, it does not frequent landfills. It picks food items from the surface of the water or from the ground in shoreline habitats, and will often dive shallowly from flight in order to reach prey that is below the surface of the water. It regularly engages in piracy, or ‘kleptoparasitism’, in which it chases and harasses other seabirds to encourage them to drop or disgorge whatever food they are carrying so that it can be stolen. The skuas and jaegers are experts at this type of behaviour, and some Heermann’s Gulls in B.C. have been observed to follow jaegers during these chases and pick up bits of disgorged food that are not taken by the jaeger. This species also congregates around foraging marine mammals (especially sea lions) in order to pick at the scraps of meat that are dispensed into the surrounding waters. It sometimes becomes very tame in areas that are frequented by people, and will sometimes even accept handouts of bread.

Source: Islam (2002); Campbell et al. (2007)

Habitat


The Heermann’s Gull is strictly a marine species throughout its range. It frequents a variety of marine habitats, although it shows a preference for areas of high water turbulence such as tidal rips, surge channels, and areas of upwelling. It tends to avoid areas of heavy freshwater influence, such as the heads of inlets or the mouths of major rivers, although it is occasionally observed in the Strait of Georgia among large mixed-species gull flocks at the mouths of creeks and rivers. Roosting birds commonly congregate on rocky offshore islets, headlands, reefs, jetties, log booms, kelp beds, or sandy beaches, often in the company of California Gulls or Glaucous-winged Gulls. It forages both in inshore waters as well as offshore waters, although it is usually within ~8 km of the shore.

Source: Campbell et al. (1990b); Campbell et al. (2007)

Distribution

Global Range

Most of the world’s population breeds in the Gulf of California in western Mexico, with small numbers breeding on islands off the west coast of Baja California. This species has occasionally attempted to nest in coastal California, but all nesting attempts have proved unsuccessful. It winters along the Pacific coast from central California to central Mexico, and large numbers of post-breeding wanderers occur north along the coast every summer and fall, regularly reaching the south coast of B.C.
BC Distribution

Non-breeding
Locally common post-breeding wanderer (summer, fall) to the south coast of the province, with the largest numbers occurring along the west coast of Vancouver Island (generally north to the Tofino area, smaller numbers north to the Brooks Peninsula), in the Strait of Juan de Fuca, and in the southern Gulf Islands. It is generally rare and local in the Strait of Georgia, although it occurs in larger numbers (and is considered uncommon) in southern portions of the strait. It is very rare on northern Vancouver Island, including Queen Charlotte Strait and Johnstone Strait, and is casual to very rare farther north along the central mainland coast and in the Queen Charlotte Islands.

This species has been recorded in all months in B.C., but the vast majority of individuals occur during summer and fall. It first begins to appear in B.C. in mid- to late June, and populations quickly build throughout July to reach a peak in August. The number of birds then gradually decreases throughout September and October, and almost all birds have left the province by early to mid-November (the latest individuals generally lingering in the Strait of Juan de Fuca or the southern Strait of Georgia). This species is then very rare in the Strait of Juan de Fuca and southern Strait of Georgia throughout the remainder of the winter and through the spring. The largest numbers of birds at any time of the year are found in the Strait of Juan de Fuca, with late summer concentrations in this area regularly numbering into the hundreds of individuals (exceptionally 1,000+).

Vagrancy
This species is accidental away from the immediate coast, with a single late fall (November) record for Harrison Lake in the lower Fraser Valley.

Source: Campbell et al. (1990b); Bradshaw (2007); Campbell et al. (2007)

Conservation

Population and Conservation Status

The global population of Heermann’s Gulls has been steadily increasing for the past 40-50 years following the cessation of egg-collecting activities at its Mexican breeding colonies in the 1960s. The number of breeding pairs at the largest breeding colony, Isla Raza (which contains 90-95% of the entire world population), tripled over a 20-year period between the 1970s and 1990s. The number of birds recorded in B.C. also increased dramatically during the same period, and this species is now abundant in certain areas of the south coast during the late summer. Several thousand Heermann’s Gulls occur in B.C. each summer, with the largest numbers occurring during El Niño conditions. It is not a species of conservation concern in B.C.

Source: Islam (2002); Campbell et al. (2007)

Taxonomy


This species is monotypic, with no recognized subspecies. It is closely related to the Grey Gull (Larus modestus) of the Pacific coast of South America.

Source: Islam (2002)

Status Information

Origin StatusProvincial StatusBC List
(Red Blue List)		COSEWIC
NativeSUNUnknownNot Listed



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