The California Gull (Larus californicus) and Western Gull (Larus occidentalis) are two similar-looking gull species found along the west coast of North America. They can be challenging to tell apart, especially at a distance or in non-breeding plumage. However, there are some key differences between these two gulls that can help identify them.
In this article, we will go over the identification, distribution, habitat, diet, breeding, and conservation status of the California Gull and Western Gull. We will highlight the differences and similarities between these two species to help birders distinguish between them. Being able to properly identify gulls takes practice, so this guide aims to break down the key points into an easy-to-use reference.
Identification
The California Gull and Western Gull are medium-sized gulls with gray backs, white undersides, and yellow legs. In basic plumage, adults of both species have gray backs, white underparts, black wingtips with white spots, and yellow legs and feet. The bill is greenish-yellow with a reddish spot near the tip (though this is variable).
Here are some tips for telling them apart:
Size and Structure
– The California Gull is smaller with a more slender, elegant look. The Western Gull is stockier and 25% heavier on average.
– The bill of the California Gull is smaller and more delicate. The Western Gull’s bill is heavier.
– The legs of the Western Gull are longer and thicker than the California Gull’s legs.
Head
– Adult California Gulls have a round head that appears rather petite. Western Gulls have a larger, blockier head.
– The eye of the California Gull sits higher on the head. The Western Gull’s eye is more centered on the head.
– Western Gulls have more extensive black markings around the eye. This gives them a “meaner” look compared to the California Gull.
Plumage
– In basic plumage, the mantle (back and wings) of the California Gull is a paler gray compared to the darker gray of the Western Gull. The California Gull’s gray has been described as more “glaucous.”
– California Gulls have thinner and daintier black markings on the wingtips compared to the broader black markings of Western Gulls. The white spots on the wingtips also tend to be smaller on California Gulls.
– Western Gulls have darker gray on the underside of the flight feathers compared to the paler underside of California Gulls. This creates a two-toned look underneath.
– During the breeding season, adult California Gulls develop a reddish orbital ring around the eye. Adult Western Gulls show a reddish blotch near the angle of the jaw instead.
Behavior
– The flight style of the California Gull appears more tern-like and graceful compared to the heavier flight of the Western Gull.
– California Gulls frequently tip forward when resting on the water, dipping their bills into the ocean. Western Gulls tend to float flat on the water instead.
– Western Gulls are generally louder, more aggressive, and more territorial compared to the more delicate California Gull.
Distribution
The ranges of these two gulls overlap along the Pacific Coast, but there are some key differences:
California Gull
– Breeds inland at lakes and marshes across western North America from British Columbia down to northern Baja California. Winters along the coast from southern Alaska to Mexico.
– The largest breeding populations are at Great Salt Lake in Utah and Mono Lake in California.
– Smaller numbers breed in southwestern Canada and the Pacific Northwest. Also breeds sporadically farther east to Manitoba and Minnesota.
– Migrates south along the coast of California and to the Mexican mainland in winter.
Western Gull
– Breeds along the Pacific Coast from Washington state south to Baja California in Mexico.
– Does not migrate and can be found year-round within this coastal range. Northern populations may wander south in winter.
– In California, breeding is concentrated on the offshore islands of southern California and the Channel Islands. Farther north their breeding range is more continuous along the coast.
– They are rare north of Washington apart from vagrants and winter wanderers.
So in summary, the California Gull breeds mostly inland and farther north, migrating south and coastally in winter. The Western Gull sticks close to the immediate Pacific Coast year-round.
Habitat
The habitat preferences of these species also differ:
California Gull
– Nests colonially on islands in large inland lakes and marshes. Requires shallow, protected waters for nesting.
– In migration and winter frequents coastal habitats including beaches, harbors, bays, and offshore waters.
– Forages in open water and along shorelines. Roosts on beaches, breakwaters, jetties, and offshore rocks.
Western Gull
– Nests colonially on offshore islands, rocky islets, remote coastlines, and less frequently on coastal mainland sites.
– Found year-round in coastal and nearshore marine environments including harbors, bays, beaches, and jetties.
– Forages in shallow ocean waters, tidal flats, beaches, and along the surf line. Roosts on beaches, wharfs, buoys, and offshore rocks.
– Occurs less frequently on large inland lakes.
So in a nutshell, the California Gull uses more freshwater inland lakes for breeding while the Western Gull is truly a coastal species focused on the marine environment.
Diet
The diets of the California Gull and Western Gull are broadly similar, though with some key differences:
California Gull
– Feeds opportunistically on small fish, aquatic invertebrates, and terrestrial insects.
– At inland lakes, common prey includes brine shrimp, brine flies, midges, and alkali flies.
– Along the coast eats fish, squid, worms, crabs, and shrimp. Forages in shallow waters.
– Opportunistically feeds on the eggs and young of other birds. May also eat small rodents.
– Scavenges dead fish and garbage at fisheries, harbors, and landfills.
Western Gull
– Generalist predators and scavengers that feed on a wide variety of marine life.
– Common prey includes crabs, sea urchins, squid, krill, fish, and other seabirds.
– Scavenges on dead fish, fish scraps, and refuse at harbors and wharfs.
– Forages in the surf zone and offshore. May dive from the surface for submerged prey.
– Often feeds on intertidal organisms in the rocky intertidal zone and tidal flats during low tide.
– Kleptoparasitizes other seabirds by stealing fish from them.
– Opportunistically preys on eggs, chicks, and adults of other nesting seabirds. Also eats rodents and insects.
So while both are omnivorous gulls, the Western Gull is more adapted to feed on marine organisms in the coastal zone while the California Gull makes use of inland freshwater food as well.
Breeding
California Gull
– Nests colonially, often in mixed colonies with other gull species. Colonies range from a few dozen to over 10,000 breeding pairs.
– Breeding begins at 2-3 years old. Forms long-term pair bonds and exhibits mate and nest site fidelity in subsequent years.
– Nest is a shallow scrape lined with vegetation, feathers, debris, or garbage. Both parents help build the nest.
– Lays 1-4 eggs (usually 2-3). Eggs are light brown to olive with dark brown spotting. Incubation is 23-27 days.
– Both parents share incubation duties. Chicks hatch downy and precocial. Fledge at 4-6 weeks old.
– Fall migration starts in August, with most birds migrating south by late September.
Western Gull
– Breeds colonially on coastal islands, sometimes intermixed with other seabird species. Colonies range from a few pairs up to 25,000 nests.
– Starts breeding at 3-4 years old. Mates for life. Exhibits strong nest site fidelity year to year.
– Bulky nest built of vegetation and debris. Nest lining includes seaweed, feathers, paper, plastic, and shells.
– Lays 1-3 eggs (usually 3). Eggs are brown to olive with dark splotches and scrawling. Incubation takes 26-28 days.
– Shared parental care. Semiprecocial downy chicks fledge in 5-6 weeks.
– Stays within breeding range year-round. Disperses locally after breeding season.
The California Gull is a highly migratory species while the Western Gull occupies a smaller home range around breeding colonies along the coast.
Conservation Status
The California Gull and Western Gull differ in their conservation needs and population trends:
California Gull
– Estimated global population of 500,000 to 1 million individuals. Population increasing.
– Listed as Least Concern on the IUCN Red List due to large and increasing population size and range.
– Historically relied on just a few key breeding colonies. Conservation efforts expanded available habitat, allowing population growth.
– Major threats include habitat degradation, human disturbance, pollution, shooting, and climate change impacts at breeding sites.
Western Gull
– Global population estimated at 122,000-152,000 mature individuals. Population declining.
– Listed as Near Threatened on the IUCN Red List due to decreasing population trends.
– Coastal habitat loss and disturbance, ocean pollution, oil spills, and climate change impacts are major threats.
– Competition and predation from expanding Western Gull populations also a concern for other seabird species.
– Management efforts needed to protect breeding colonies and restore coastal habitats.
While the California Gull has rebounded well, the Western Gull is a species of growing conservation concern along the Pacific Coast due to its small and declining population.
Summary of Differences
| Trait | California Gull | Western Gull |
|---|---|---|
| Size | Smaller and more delicate | Larger and stockier |
| Bill Size | Smaller and thinner | Thicker and heavier |
| Head Shape | Round head, small appearance | Large blocky head |
| Eye Location | Eye higher on head | Eye more centered |
| Plumage Tone | Pale gray mantle | Darker gray mantle |
| Wing Markings | Smaller wingtip markings | Broad black wing markings |
| Breeding Plumage | Red orbital ring | Red spot near jaw |
| Flight Style | More tern-like and graceful | Heavier flight style |
| Behavior | More delicate and timid | Noisy, aggressive, territorial |
| Breeding Range | Inland lakes and marshes | Coastal islands |
| Winter Range | Coastal; migrates south | Year-round coastal resident |
| Diet | More inland insects and brine shrimp | Marine fish, invertebrates |
| Conservation Status | Increasing population | Decreasing population |
Conclusion
In summary, the California Gull is smaller, daintier, and paler in coloration than the more robust Western Gull. The California Gull has a more inland, freshwater focus for breeding and shows migratory movements, while the Western Gull sticks closely to the Pacific Coast year-round. pay attention to differences in structure, plumage tones, and behavior to help distinguish these tricky lookalike species. The California Gull is thriving, but conservation concerns for the Western Gull make proper identification important for population monitoring. With careful observation and practice, birders can master separating these two West Coast gulls.
