Larus occidentalis, commonly known as the Western Gull, is native to the Pacific coast of North America. Its geographical distribution spans from British Columbia in Canada, through the western United States, and extends as far south as Baja California, Mexico. It is predominantly found along coastal regions and offshore islands.

The Western Gull inhabits coastal environments, where it thrives in marine and estuarine ecosystems. It prefers rocky and sandy shorelines, cliffs, islands, and occasionally visits human-altered environments such as ports and urban waterfronts. The climate in its native region is typically mild, with coastal fog, marine winds, and moderate rainfall, reflecting a maritime influence.

The Western Gull is an opportunistic feeder with a diet consisting mainly of marine invertebrates, fish, and scavenged food. It plays a crucial role in the coastal ecosystem by helping control the populations of its prey and scavenging on carrion, thus contributing to nutrient cycling. It is well-adapted to its coastal habitat, with strong flying abilities that allow it to travel across long distances for foraging.