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Sea Birds - Gulls
Gulls are found throughout the world. Three varieties, the herring gull, the California gull, and the western gull are seen in the Sea Lion Caves' vicinity. Seagulls are just one of many different kinds of birds that choose to live along the seashores. Food is usually plentiful for all the birds, although seagulls have been known to follow a large ship across the ocean, feeding on the garbage thrown overboard. But generally seagulls are not found far out at sea. And as a result, the early explorers were always happy to see a group of seagulls flying overhead, because it meant that land was near.
Sea Birds - Western Gull
The western gull is the most common gull seen near the Caves. The adult has a wingspan of 24 to 27 inches, and is buff and olive colored, mottled with white or shades of brown. It generally nests on the rocky ledges above the cormorants and lays two to three eggs.
The western gull has a small population, with limited distribution along the west coast of North America. Even though gulls prey on other birds, they don’t deserve their reputation of being a nuisance or an undesirable pest. For example, their breeding areas were once destroyed because people thought the gulls preyed on black-crowned night herons, when actually the opposite is true. The western gull feeds largely on small, surface-feeding fish of no use to sport fishermen.
To break open the shells of their prey like sea urchins and clams western gulls drop them from high in the air to hard surfaces below. They also harass cormorants and pelicans, forcing them to regurgitate their catch, which the gulls quickly gobble up. Western gulls feed on refuse only when natural prey is scarce. Birds that feed on refuse sometimes have lower breeding success. Western gulls aren’t shy birds. They often invite themselves to the otter feeding programs at the aquarium.
Most Western Gull breed every year, although some forego breeding in years when food supply is poor. Modal clutch size 3, but some birds in poor condition lay 2 or even 1 egg. Only 1 successful clutch/season because producing fledged offspring takes minimum of 10 wk (typically 15 20 wk). Up to 2 replacement clutches are possible if early clutches are destroyed.
Many adults Western Gull die of injuries (broken wings, beaks, etc.) incurred by flying into obstacles in high winds or by fighting with co specifics. Others are shot or poisoned by anglers who regard gulls as competitors for fish. This species almost certainly takes in contaminants, e.g., chlorinated hydrocarbons, bacterial toxins, during feeding, especially on human refuse. Tangle in nets, fishing lines result in significant mortality. A few bird are taken by a wide variety of predators. Most mortality occurs during breeding season.
Western Gull feeds primarily on natural prey at sea, so pesticide contamination from food, and oil spills around foraging grounds and breeding colonies, are human activities most likely to affect populations. Early population increases in the 1940s through 1960s were attributed to increased food availability from feeding on human refuse. Diet studies do not support this hypothesis, since Western Gulls feed on refuse only during poor feeding conditions.
Sea Birds - Herring Gull
The herring gull (Larus argentatus) is approximately the same size as the western gull but it has a somewhat lighter mantle. It lays as many as four eggs and sometimes nests in trees instead of the rocky cliffs.
Herring Gull communication has been studied for several decades. A gull states its intent to stand fast by giving the trumpeting “long call.” It threatens to peck a neighbor by drawing itself up to look bigger, lowering its bill tip ready to strike, and pulling its “wrists” out of its body feathers. Then it steps stiffly towards its opponent.
Sea Birds - Herring Gull - Physical characteristics
The adult Herring Gull is about 61 cm long from the tip of its bill to the tip of its tail. Its head, body, and tail are white, its bill is yellow with a red spot on the lower tip, and its legs are pink or flesh-colored. The backs and upper wing surfaces of adult gulls are gray, and the tips of their outermost flight feathers are black with a white spot. In winter, the heads of adult gulls are streaked with brown. Immature birds are a mottled brown and take four years to develop full adult plumage.
Sea Birds - Herring Gull - Habitat
Herring Gulls are one of the most widespread species in Canada. Indeed, their breeding range includes every province and territory in Canada. Their main no breeding range includes the Pacific and Atlantic coasts, the southern United States, the coast of the Gulf of Mexico, and a few Caribbean islands. In the lower Great Lakes area, the species can be found year-round.
Of the 43 species of gull found in the world, 16 have bred in Canada, but three have nested only occasionally. Specialized feeding techniques and different ranges prevent, or at least reduce, competition between species.
Sea Birds - Herring Gull - Food
Herring Gulls regurgitate, or bring up; food remains that they cannot digest. Analyses of these “pellets” and of their feces show that Herring Gulls, like most other gull species, will eat almost anything clams, small fish, floating dead animals, small young and adults of other nesting birds, bread, French fries, etc.
They have a knack for finding places where food is abundant, such as fish wharves and garbage dumps. Diet studies in the Great Lakes area showed that most pellets in colonies near large urban centers contained remains of garbage as well as various fish species. Pellets in colonies near agricultural areas often had the remains of small mammals, notably deer mice.
Individual Herring Gulls tend to specialize in particular types of food or feeding techniques. Within a large colony, some birds may regularly visit dumps, while others may feed entirely on fish and crabs found on the seashore. A few individuals take to cannibalism, watching their neighbors for an opportunity to sneak in and remove an egg or chick. These birds are often breeding birds that have lost their own brood. Although large numbers of Herring Gulls in North America are almost entirely dependent on human activities for their food, there are still populations breeding on offshore islands or in remote parts of the low Arctic that exist on a natural diet.
Sea Birds - Herring Gull - Reproduction and Breeding
Courtship begins as soon as birds arrive at the colony in the spring, usually mid-March. Once pairing has taken place, the birds build a nest or, more often, refurbish an old one. The nest is circular and lined with moss or grass, which is also used to build up the rim. In most areas, a group or clutch of three eggs will be laid by mid-May. Eggs are normally incubated, or kept warm until they hatch, for 26 to 28 days.
Females laying for the first time, usually in their third or fourth year, often lay only one or two eggs. They also tend to lay later in the season than more experienced birds, which generally make up about three-quarters of the breeding population.
Eggs are well looked after, but they can be lost. Some are eaten or stolen by other gulls, and others are washed away by storms. Birds that lose their eggs early in the season will usually lay additional eggs to replace the ones that were lost.
The greatest losses in the colony are usually of tiny chicks in the first few days after hatching, probably as a result of predation by neighboring gulls. When they start to run about, chicks do not know the borders of their parents’ territory, and the adults have to guard them against neighbors who would kill trespassers. Spots on the top and back of the chick’s head identify each chick individually; the adults learn these markings in the first few days. These spots are the last of the downy plumage to be lost.
Sea Birds - Herring Gull - Colonies
In winter, Herring Gulls are most likely to congregate on beaches along the shores of oceans and other large water bodies. In other seasons, gulls may range inland and can be found beside lakes and rivers, in grassy meadows, or on garbage dumps, golf courses, islands, cliffs, and buildings. Their main habitat requirement is a dependable source of food nearby.
Herring Gulls can be quite useful, keeping our beaches clean by eating dead fish and other garbage and leading fishing boats to schools of herring, one of their favorite foods, hence the name “herring” gull. On the other hand, the gulls will steal any fish catch left unattended for any length of time, and their excrement, or bodily waste, often damages the roofs of buildings where the gulls roost, or settle for rest.
Herring Gulls will nest in a variety of sites, but always near a body of water. On offshore islands, they frequently occupy flat ground. On the mainland, however, they tend to nest on cliffs, probably to avoid predatory mammals. In some places where food from human activities is abundant, they have begun to nest on roofs and window ledges of buildings. On cliffs, Herring Gulls tend to nest on turf-covered ledges.
Herring Gulls are very social birds and prefer to nest in colonies. Once a colony is well established, they are faithful to it and reluctant to settle elsewhere. In the lower Great Lakes area, for example, older, experienced breeding birds usually stay close to their colonies and are the first to reoccupy nesting territories in early spring. Some may use the same nesting site for as long as 10 to 20 years.
As the colony grows, some birds are unable to establish breeding territories. Sooner or later, these birds start to hang out near abundant food supplies. As the urge to breed grows, some start nesting at the new site, and the rush is on. In a very few years, the new colony may grow to capacity.
Although at first glance a Herring Gull colony may seem noisy and disorderly, there is some organization to it. Each pair occupies an area from which they drive other gulls and on which they nest.
When the Herring Gull population is dense, gulls will occupy all suitable places in their feeding area (as distinct from the colony). Adults on feeding areas drive away intruding gulls. If the fledglings (young Herring Gull chicks that have just started to fly, usually at about six weeks of age), already at a disadvantage because of their inexperience, were excluded from these feeding areas, their survival would obviously be endangered. However, chicks can lessen the adults’ territorial aggressiveness on the feeding areas by assuming a hunched posture, pumping their heads, and voicing shrill calls. The same behavior causes parents to feed their chicks on the breeding colonies. Such adaptations reduce the rate of death of chicks at the times when they are most vulnerable.
Sea Birds - California Gull
The California gull is seen only on rare occasions near the Caves. It is considerably smaller than the western and herring gull, its color is browner and it prefers inland water, particularly for nesting.
All three types of gulls feed on refuse and fish and become quite tame in the presence of humans. But it is interesting to note that if a predator such as an eagle or hawk enters the nesting area, the gulls will immediately attack in forces of 100 or more, chasing the intruder away or even forcing it into the water to drown.
The California Gull is a medium-sized gull with a length of 17 inches and a wingspan of 52 inches. It is slightly smaller than the Herring Gull, but resembles it in all plumages. The California Gull has a bright yellow bill with a red spot at the gooneys. The legs are yellow, the eye is brown, the head, neck, breast and belly are white, the back and upper wings are gray, and the primaries are black with white tips. Juveniles are brown with dark brown primaries and tail.
California gull is common along the Pacific Coast in winter and inland in breeding season, nesting in large colonies on the prairies. During the breeding season it prefers barren islands on fresh, brackish or alkaline lakes, shores of lakes or ponds and marshes. Preferred nesting sites have sparse vegetation with the nest a scrape on the ground in elevated, boulder-strewn areas.
The clutch size is from 1 to 3 eggs. The incubation period is about 25 days. It takes the young about 45 days to fledge. There is one brood per year. Diet consists of insects, carrion, aquatic invertebrates, earthworms, young birds, fish and rodents.