Aside from skimmers and two species of gulls, most members of the gull and tern family are diurnal, active during the day. During the breeding season, gulls and terns nest in small or large colonies. Terns in particular are found in very large groups that may include millions of individuals. Gulls and terns
Female skuas usually lay two eggs at a time. The two skua eggs hatch asynchronously (ay-SIN-kron-us-lee), that is, one egg hatches two or three days before the other. Asynchronous hatching allows the first chick to be larger and stronger than the other. In years where there is little food, parents can usually raise only one chick and so only the first chick survives.
are territorial during the breeding season, defending a small area around the nest from other individuals of the species. Most gulls and terns will mob potential predators and intruders, with many birds attacking simultaneously. This strategy is very successful against other bird species, but does not work as well with mammalian predators.
Skimmers are nocturnal, active at night. They nest in colonies, sometimes ones that include gulls and terns. The members of a skimmer pair usually face in opposite directions while at the nest to more effectively scan for predators. Skuas and jaegers tend to be found alone, although they sometimes form foraging flocks over schools of fish.
Gulls, terns, and their relatives are monogamous (muh-NAH-guh-mus), with each male breeding with a single female. In many species, individuals keep the same mates from one year to the next. Pairs that stay together are often able to raise more young than newly mated pairs. However, in many gulls, individuals of both sexes sometimes copulate, breed, with birds other than their mates. Both male and female participate in incubating, or sitting on the eggs, defending the territory from intruders, and feeding and protecting the young once they hatch. Females lay one to three eggs at a time. The eggs are usually brown with dark markings. Eggs hatch after twenty to thirty days, and chicks are able to fly after four to six weeks. If the eggs or chicks are lost, particularly early in the breeding season, the female will often lay a new set of eggs. Chicks generally remain with their parents for some time after leaving the nest, particularly among the terns, where young have to learn the difficult art of diving for food. Some young terns will migrate with their parents and spend much of the winter with them.
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