This species is essentially confined to the coast, staying on a few kilometres inland. It has a very varied diet, including marine fish and invertebrates, eggs, chicks and adults of seabirds, carrion, spawning salmon, and it may attack and kill newborn seal pups. Some males may establish feeding territories in alcid or cormorant colonies feeding mainly by predation, piracy and scavenging, occupying the same territory year after year. It also drops shellfish on to rocks to break them. It lays from late April or early May, and later in the north, nesting on barren substrates in colonies on rocky islets with some herbaceous cover and gravelly beaches. Some populations are migratory whilst others are sedentary, and individuals tend to disperse depending on food availability (del Hoyo et al. 1996).

The Western Gull is found on the Pacific coast of North America, ranging from Vancouver Island (Canada) to the southern tip of Baja California (Mexico), and breeding from north-west Washington (USA) to central Baja California (Burger et al. 2018).