Bird Fact Friday — Hybrid Gulls

Adapted from page 189 of Gulls Simplified:

Many gull species are closely related, with their evolutionary divergence fairly recent, and their geographic isolation is not always absolute. In fact, the ranges of some genetically similar species overlap. Because of this fertile combination of genetic similarity and physical proximity, hybridization between similar species currently considered distinct is both likely and problematic.

The offspring of theses hybrid combinations often show traits of both parent species, making identification challenging, or may show the physical traits of one species but some plumage features of the other species. Being themselves fertile, these hybrid gulls may then backcross—that is, breed with either parent species or with another hybrid gull—further muddying the ID picture. Hybrids are not countable as distinct species by any ornithological organization.

The Glaucous-winged × Western Gull has the stocky body and heavy bill typical of Western Gull, as well as the head shape of that species with a bump on the crown. However, the back is gray like that of Glaucous-winged, but the wing tips are too dark for that species. Photo credit: Kevin Karlson

For example, the Glaucous-Winged × Western Gull is the most common hybrid gull encountered in North America, and it occurs mostly on the Pacific coast from California to British Columbia. In certain areas of northern Oregon and southern Washington, hybrids may outnumber pure individuals of both species. Some hybrids resemble Western Gulls,especially in body and bill structure, but show some plumage traits of Glaucous-winged, while others resemble Glaucous-winged in structure and bill shape but show some plumage features of Western Gull.

Gulls Simplified
A Comparative Approach to Identification
By Pete Dunne and Kevin Karlson

This unique photographic field guide to North America’s gulls provides a comparative approach to identification that concentrates on the size, structure, and basic plumage features of gulls—gone are the often-confusing array of plumage details found in traditional guides.

Featuring hundreds of color photos throughout, Gulls Simplified illustrates the variations of gull plumages for a variety of ages, giving readers strong visual reference points for each species. Extensive captions accompany the photos, which include comparative photo arrays, digitized photo arrays for each age group, and numerous images of each species—a wealth of visual information at your fingertips. This one-of-a-kind guide includes detailed species accounts and a distribution map for each gull.

An essential field companion for North American birders, Gulls Simplified reduces the confusion commonly associated with gull identification, offering a more user-friendly way of observing these marvelous birds.

  • Provides a simpler approach to gull identification
  • Features a wealth of color photos for easy comparison among species
  • Includes detailed captions that explain identification criteria and aging, with direct visual reinforcement above the captions
  • Combines plumage details with a focus on size, body shape, and structural features for easy identification in the field
  • Highlights important field marks and physical features for each gull
This post is part of a series, explore additional posts here<< Bird Fact Friday — Ross’s GullBird Fact Friday — the Great Black-Backed Gull >>