California gulls, L. californicus, should not be confused with western gulls, Larus occidentalis, which are more commonly seen along California's coastline.
Vocalized sounds serve as the main form of communication for California gulls. Young chicks use begging calls to let the parents know when they are hungry. As the birds get older the sounds increase in volume. When a predator enters the colony the gulls issue a warning call by dropping the pitch of the sound and stressing the second syllable. The mew call is a series of soft low notes used during courtship, courtship feeding, and copulation. When a mate returns to the nest to exchange duties with its partner, the mew call is also used. Furthermore, the mew sound is used in territorial conflicts. When the female gull wants her mate to feed her, the begging call is used. The copulation call is used solely by the male during copulation. California gulls use an alarm call of several sharp notes in response to the threat of a predator. When chasing or attacking a predator, the birds sound the charge call. If a bird is captured and struggling to escape, it emits the shrill waver, a hoarse thin call. (Bent, 1939; Winkler, 1996)
Members of this species also communicate through their posture. If a gull feels threatened, it holds its wings slightly away from its body. As a California gull prepares to attack, it gets into the lunge position. Pulling grass from the ground is another threat to other animals. Fights between individuals usually occur between two birds of the same sex. These physical demonstrations are often used along with calls. (Winkler, 1996)
Communication Channels: visual ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
The world-wide population of California gulls is somewhere between 500,000 and 1 million birds and growing. The gulls are not often killed by humans because they are usually appreciated for their benefits to agriculture. Occasionally gulls are killed by six-pack drink carriers which get caught around the gulls' necks when they feed on trash from garbage dumps. This can easily be prevented by cutting up the plastic before throwing it away.
California gulls are protected under the Migratory Bird Treaty Act, but are not listed by the IUCN, the US Federal List or CITES.
US Migratory Bird Act: protected
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
The young birds leave the territory of their parents forty to sixty days after they are born. By this time they are almost fully grown; however, feathers are still developing. The birds usually achieve their adult plumage and reach sexual maturity after four years. After leaving the parental colony, fledglings gather at the edge of water and swim together, usually forming groups at areas where substantial food is available. The ability of the birds to fly and feed improves to an adult level after around a month after they have left the territory of their parents.(Hobert, 2000; Winkler, 1996)
While California gulls help farmers more often then not, recently they have caused problems by ravaging cherry crops. The birds beat the cherries off the trees and then collect and eat the fallen fruit from the ground.
Negative Impacts: crop pest
California gulls are famous for reputedly aiding settlers in Salt Lake City, Utah, by eating the "locusts" (probably Mormon crickets, Anabrus simplex) that threatened their crops. California gulls benefit agriculturalists economically because they feed on the pests that destroy their crops, such as mice, and insects. Mouse holes often ruin crops, but as the fields are irrigated, mice are forced to come out of their holes and they are then eaten by the birds. Also, California gulls pick up trash along the edges of rivers and lakes, helping to keep areas free from garbage.
Positive Impacts: controls pest population
California gulls have an impact on the prey they consume.
Food preferences vary with the location of the bird's habitat. Favorite foods of California gulls include fish, birds, small mammals such as gophers and mice, garbage, insects, and aquatic invertebrates.
The birds use a range of different techniques to capture food. They often retrieve food such as fish near the surface of the water or brine shrimp by diving and pecking. The gulls capture small mammals like mice that have been flooded out of their holes by irrigation. In some instances the birds steal the eggs and chicks of other gulls in the colony. California gulls eat plant foods such as grains, vegetables, and especially cherries. The birds knock the cherries off the trees and then pick them up off the ground. They can also be found at garbage dumps dining on scraps of trash.
Animal Foods: birds; mammals; fish; eggs; insects; aquatic crustaceans
Plant Foods: seeds, grains, and nuts; fruit
Primary Diet: omnivore
California gulls are North American birds. They are found in regions of Mexico, the west coast of the United States, the Great Plains, and western Canada. The species has been reported to live in California, Colorado, Kansas, Nevada, North Dakota, Oregon, Texas, Utah, Washington, and Wyoming. The birds are found in different regions depending on the season. In the summer, during breeding season, they are found in parts of northwestern Wyoming, northern Utah, western Nevada, and northern California. During the winter, California gulls can be observed on the Pacific coast from southern British Columbia to southern Mexico. The gulls migrate to North Dakota, British Columbia, lower California, and Monterey, California during the spring. In the fall the gulls migrate southwest to the coast in the states of Washington, Oregon, and California.
Biogeographic Regions: nearctic (Native )
California gulls live in areas that contain lakes, marshes, and along the seacoast. They also reside on offshore islands, near rivers, agricultural land, and garbage dumps. When breeding, they often construct their nests near shrubs by bodies of water.
Habitat Regions: temperate ; terrestrial
Aquatic Biomes: lakes and ponds; rivers and streams; coastal
Wetlands: marsh
Other Habitat Features: urban ; agricultural ; riparian
The lifespan of California gulls is usually between 4 and 24 years (20 on average). The oldest known California gull reached 30 years. Causes of death include exposure to cold weather, predation, parasitism, and competition with other species.
Range lifespan
Status: wild: 30 (high) years.
Typical lifespan
Status: wild: 4 to 24 years.
Average lifespan
Status: wild: 20 years.
The average California gull is around 54 cm long and weighs about 600 g. While there are no differences in male and female plumage, males are usually larger than females, with a larger bill, head, and tarsi. When the bird is newly born it has a thick, soft down of light colors that blend in with the surrounding environment. By the juvenile's first winter, it has a brown mantle and wings, a brown head, and pink tinted legs. When the bird is around two years old the tail becomes white and the bill turns yellow. When the gull reaches its third year, it almost is completely like the adult in appearance, but the adult bill pattern and wing pattern are not completely developed. By the fourth winter the bird has an adult's white head, dark grey mantle, yellow green legs, reddish eye ring, and black wingtips.
Range mass: 432 to 885 g.
Average mass: 600 g.
Range length: 51 to 58 cm.
Average length: 54 cm.
Sexual Dimorphism: sexes alike; male larger
Other Physical Features: endothermic ; bilateral symmetry
When a bird predator such as an eagle approaches the colony, the gulls respond with alarm and warning calls. When a coyote enters the colony, gulls may dive at it and sound warning calls. If a human comes into a gull colony the response will be even more severe. It is not uncommon for California gulls to attack humans by plunging at them.
Young gulls have cryptic coloration that helps to protect them from predators.
Known predators include: great horned owl (Bubo virginianus), golden eagle (Aquila chrysaetos), bald eagle (Haliaeetus leucocephalus), prairie falcon (Falco mexicanus), red-tailed hawk (Buteo jamaicensis), herring gull (Larus argentatus), red fox (Vulpes vulpes), weasel (family Mustelidae), feral dog (Canis lupus familiaris), muskrat (family Muridae), gopher snake (Pituophis catenifer sayi), northern pike (Esox lucius), Canada goose (Branta canadensis), raccoon (Procyon lotor), skunk (family Mustelidae), river otter (Lontra canadensis) and other California gulls.
Known Predators:
Anti-predator Adaptations: cryptic
The "Head-Tossing Display" and the "Begging Call" are used to prompt copulation or courtship-feeding in California gulls. The ritual of courtship-feeding where the male bird delivers food to the female may occur during the pre-egg laying and early egg-laying stages. The "Head-Tossing Display" and "Begging Calls" can be used by either males or females to iniciate copulation. During copulation the male jumps onto the female's back and gives the "Copulation Call". Pairs usually remain together each breeding season, but in some cases partners change.
Mating System: monogamous
California gulls return to their home colony each year about three to seven weeks before they begin to lay their eggs. The breeding season occurs from May to July. Once a pair has formed, and the nest has been in the process of construction for around a week, egg laying begins. The birds lay one egg every other day until they have laid between two to five eggs. The eggs hatch after about 24 days and the chicks fledge within 40 to 60 days. A second brood is laid only if the first was unsuccessful. The birds usually build their nests close to shrubs by water sources such as marshes, ocean coasts, or lakes. Young birds reach sexual maturity after 4 years.
Breeding interval: California gulls breed once yearly
Breeding season: May to July
Range eggs per season: 2 to 5.
Average eggs per season: 3.
Range time to hatching: 23 to 26 days.
Average time to hatching: 24 days.
Range fledging age: 40 to 60 days.
Range age at sexual or reproductive maturity (female): 4 to 4 years.
Range age at sexual or reproductive maturity (male): 4 to 4 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous
Average eggs per season: 3.
The male and female take turns incubating; the nonincubating parent guards the nest and hunts for food. In rare cases the chick will be smothered by the parent while it is trying to hatch because the parent is sitting too securely on the egg. Both parents feed the precocial offspring until they fledge. The parents swallow food, take it back to the nest, and regurgitate it in order to feed it to their young.
Parental Investment: no parental involvement; precocial ; pre-hatching/birth (Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female)
