Saturday, November 2, 2013

All About Seagulls

The other day during my drive north I stopped at a rest area.  There were several seagulls begging to the tourists.  As I took pictures of them, I realized that I really don't know that much about seagulls.

Gulls or seagulls are seabirds of the family Laridae in the sub-order Lari.   Gulls are typically medium to large birds, usually grey or white, often with black markings on the head or wings. They typically have harsh wailing or squawking calls, stout, longish bills, and webbed feet. Most gulls, particularly Larus species, are ground-nesting carnivores, which will take live food or scavenge opportunistically. Live food often includes crabs and small fish. Gulls have unhinging jaws which allow them to consume large prey.  The large species take up to four years to attain full adult plumage, but two years is typical for small gulls. Large White-Headed Gulls are typically long-lived birds, with a maximum age of 49 years recorded for the Herring Gull.

Gulls nest in large, densely packed noisy colonies. They lay two to three speckled eggs in nests composed of vegetation. The young are born with dark mottled down, and are mobile upon hatching.

Gulls are resourceful, inquisitive and intelligent birds, demonstrating complex methods of communication and a highly developed social structure. For example, many gull colonies display mobbing behavior, attacking and harassing would-be predators and other intruders. Certain species  have exhibited tool use behavior, using pieces of bread as bait with which to catch goldfish.  Many species of gull have learned to coexist successfully with humans and have thrived in human habitats.  Gulls have been observed preying on live whales, landing on the whale as it surfaces to peck out pieces of flesh.

Gull species range in size from the Little Gull, at 4.2 ounces (120 g) and 111.5 inches (29 cm), to the Great Black-backed Gull, at 3.8 pounds (1.75 kg) and 30 inches (76 cm).

Seagulls are generalist feeders and are the least specialized of all the seabirds.  They are quite agile and are adept at swimming, flying and walking. In fact they are more adept walking on land than most other seabirds. The walking gait of gulls includes a slight side to side motion, something that can be exaggerated in breeding displays. In the air they are able to hover and they are also able to take off quickly with little space.[

The gulls have a worldwide distribution and breed on every continent, including Antarctica and are  the high Arctic. They are less common on tropical islands, although a few species do live on the Galapagos and New Caledonia. Many species breed in coastal colonies, with a preference for islands, and one species, the Grey Gull, breeds in the interior of dry deserts far from water. There is considerable variety in the family and species may breed and feed in marine, freshwater or terrestrial habitats.

Some gull species drink salt water as well as fresh water, as they possess exocrine glands located in the skull by which sodium chloride can be excreted through the nostrils to assist the kidneys in maintaining electrolyte balance. 

Gulls are highly adaptable feeders that opportunistically take a wide range of prey. They eat fish and marine and freshwater invertebrates, both alive and already dead, terrestrial arthropods and invertebrates such as insects and earthworms, rodents, eggs, carrion, offal, reptiles, amphibians, plant items such as seeds and fruit, human refuse, and even other birds. No gull species is a single-prey specialist, and no gull species forages using only a single method. The type of food depends on circumstances, and terrestrial prey such as seeds, fruit and earthworms are more common during the breeding season while marine prey is more common in the non-breeding season when birds spend more time on large bodies of water.

Gulls are monogamous and colonial breeders that display mate fidelity that usually lasts for the life of the pair. Divorce of mated pairs does occur, but it apparently has a social cost that persists for a number of years after the break up. Gulls also return to the same colony after breeding there once and even usually breeding in the same location within that colony. Colonies can vary from just a few pairs to over a hundred thousand pairs, and may be exclusive to that gull species or shared with other seabird species.

Most gulls breed once a year and have predictable breeding seasons lasting for three to five months. Gulls begin to assemble around the colony for a few weeks prior to occupying the colony. Existing pairs re-establish their pair-bonds, and unpaired birds begin courting. Birds then move back into their territories and new males establish new territories and attempt to court females. Gulls defend their territories from rivals of both sexes through calls and aerial attacks.

Clutch size is typically three eggs, although it is two in some of the smaller species and only one egg.  The eggs of gulls are usually dark tan to brown or dark olive with dark splotches and scrawl markings, and are well camouflaged. Both sexes incubate the eggs, with incubation bouts lasting between one and four hours during the day and one parent incubating through the night.  Incubation lasts between 22 and 26 days.

In most cases the gulls found in the Grand Marais area are either ring billed gulls or herring gulls.


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