Return of Bird of the Week: Western Gull

Western Gull, Monterey Bay, California

The Western Gull is another North American west coast specialist, found from the Gulf of California to southern British Columbia. This is a big gull, easily habituated to people and perfectly willing to steal food from careless humans if given the opportunity. WC watched a Western Gull steal a hot dog from a little kid, just as the kid was about to take his first bite. The little kid was screaming in terror, frustration and anger; the gull took his prize to a nearby fence post and, unrepentant and unconcerned, ate the little kid’s tube steak. Not everybody likes Western Gulls.

Western Gulls have the darkest backs of any West coast breeding gull. It’s just a shade short of black. Pink legs, big yellow bill with a red spot on the lower mandible, and an orangish eye ring make this species a pretty easy one of identify in the field. At least it would be if it didn’t tend to hybridize with Glaucous-winged Gulls, creating a whole range of grays. In fact, in some parts of Washington’s coast, hybrid Western x Glaucous-winged make up the majority of both species.

“Hybridization and Reproductive Performance in Gulls of the Larus Glacuescens-Occidental Complex,” Douglas A. Bell, The Condor, 99:585-594 (1997)

The degree of hybridization is so high that it calls into question the idea of speciation. Ornithologists, including Douglas Bell, speculate that there are ecozones where, in the right conditions of weather and food availability, hybrids may have superior survival levels.

Under this hypothesis, hybrids would be expected to experience greater reproductive fitness in some years, whereas in other years, L. o. occidentalis will experience greater fitness. Because relative fitness within the zone fluctuates from year to year, complete swamping of parentals or complete elimination of hybrids cannot occur.

Bell, p. 592.

Western Gull in flight, second winter plumage, Monterey Bay, California

Both the male and female build the nest, a scrape in the ground lined with vegetation. There are susually three eggs, incubated about 30 days. Incubation is shared by both parents. They are brooded 3-5 days after hatching, depending on the weather. Unlike most gulls, the chicks wander away from the nest while still pretty young, but remaining in the nesting territory for about 40-45 days before fledging. The fledglings continue to associate with their parents for about three months. Survival to fledging depends upon the ENSO cycle, ranging between 50-70%. Banded birds have survived 20-25 years in the wild.

Western Gull Juvenile, San Fransisco Bay, California

There are two subspecies, split at approximately the Farallon Islands. A former subspecies in the Gulf of California, has been split into a separate species, the Yellow-footed Gull. The hybridization with Glaucous-winged and, to a lesser extent, Herring and Yellow-footed Gulls, has made the systematics of this species a real challenge.

Western Gull Adult in breeding plumage, Oregon Coast

While this is a very familiar species to anyone who has been on the West coast, the total population is only about 40,000 pairs, that breed at fewer than 200 colony sites. More than 30% of the population breed on Southeast Farallon Island. Those low population numbers, the impact of the recurrent El Niño Southern Oscillation-like (ENSO) conditions in the eastern Pacific Ocean, threats from oil spills, effects of pesticides on reproduction, the extensive hybridization, and indifference among ornithologists to its fate make the Western Gull a species of conservation concern, although the IUCN still has it as a species of Least Concern.

For more bird photographs, please visit WC’s bird photo site, Frozen Feather Images.