California gulls are medium-sized North American seabirds. Adults have a small yellow bill with a black ring, yellow legs, brown eyes, and a more rounded head. Their body is mainly white in color with grey back and upper wings. They have black primaries with white tips. Immature birds have a mottled brown and white plumage, pink legs and beak.
California gulls breed in western North America from Northwest Territories, Canada south to eastern California and Colorado. They are migratory, most moving to the Pacific coast in winter. It is only then that these birds are regularly found in western California. Their breeding habitat is lakes and marshes. During the winter they are found along the seacoasts, estuaries, bays, mudflats, near rivers, around farms and plowed fields, and even garbage dumps.
California gulls are highly gregarious birds; they often gather in big flocks and nest in colonies. They are active during the day spending most of their time feeding while flying, walking, wading, swimming and even diving for food. These birds also scavenge at garbage dumps, marinas, and docks. They frequently beg for food at public beaches, parks and other locations where people will hand feed them. They may follow plows in fields for insects stirred up by this activity. When resting, gulls often stand on one leg or sit with their eyes closed. Despite their social nature, these birds are territorial and don't tolerate other gulls in their nest areas. They chase away intruders by stretching their necks straight up and opening their bills. California gulls communicate with each other vocally and frequently utter their main repetitive "kee-yah".
California gulls are carnivores and scavengers. They mainly eat insects, fish, aquatic invertebrates, the eggs of other birds and carrion. They also eat grains, vegetables, and berries and can often be found at garbage dumps feeding on refuse.
California gulls are monogamous forming pair bonds that usually remain together for several years. The breeding season occurs from May to July. California gulls nest in colonies, sometimes with other birds. Birds build their nest is a shallow depression on the ground lined with vegetation and feathers. The female usually lays 2 or 3 eggs and both parents incubate them around 24 days. Chicks are precocial; they are covered in down and able to stand within a few hours after hatching. The young leave the nest after a few days but stay with their parents until they fledge which occurs at 40 to 60 days of age. They usually reach reproductive maturity and are ready to breed when they 4 years old.
California gulls are not threatened globally, however, in some areas, they do suffer from droughts such as on the Mono Lake (California), where one of the largest populations breeds yearly. These birds are also killed occasionally by six-pack drink carriers which get caught around their necks when they feed around garbage dumps.
According to the What Bird resource, the total number of the California gull is about 620,000 individuals. According to the All About Birds resource, the total breeding population of the species in North America is over 410,000 breeding birds. According to the University of Michigan (Museum of Zoology) resource, the total population size of the California gulls is 500,000 and 1 million birds. Overall, currently, this species is classified as Least Concern (LC), but its numbers today are decreasing.