Terns Gulls Plovers and Other Shorebirds: Charadriiformes

Some species of Charadriiformes do not migrate, remaining instead in the same area throughout the year. Other charadriiforms, however, do migrate, traveling from one area to another and back during the course of the year. Migrations generally occur between breeding grounds in the spring or summer and wintering grounds. Among the charadriiforms, shorebirds and terns are particularly well-known for their long, difficult migrations. The Arctic tern travels more than 18,000 miles each year (28,960 kilometers) between its breeding areas in the Arctic and its wintering areas in the Southern Hemisphere. The Pacific golden plover migrates between Alaska and Hawaii, a distance of 2,200 miles (3,540 kilometers), in less than two days.

Many species of charadriiforms can be found in large flocks, either during the breeding or winter season. Gulls, terns, and alcids are regularly found in groups as large as a hundred thousand individuals during the breeding season. Even larger collections of charadriiforms are found during migrations, or during the winter. In the Copper River Delta in Alaska, as many as five million shorebirds may be seen during their spring migration.

The majority of Charadriiformes species are monogamous (muh-NAH-guh-mus), meaning that a single male mates with a single female during the breeding season. In some species, individuals keep the same mate from one breeding season to the next. In monogamous Charadriiformes, both male and female help defend the nest and take care of young chicks once they hatch. Other charadriiforms have more unusual breeding systems. The jacanas are polyandrous (pah-lee-AN-drus), with a single female mating with multiple males. Still other charadriiforms, such as many species of sandpipers, are polygamous (puh-LIH-guh-mus), with a single male mating with multiple females.

Charadriiformes tend to build fairly simple nests, often just a hollow in the ground lined with a few pebbles or pieces of vegetation. Some charadriiform seabirds nest in rocky cliff areas, and lay their eggs directly on rock ledges without building any nest at all. The other end of the spectrum, some murrelets and sandpipers build nests in trees or use nests that have been built and abandoned by other bird species. Generally, females lay between one and four eggs at a time. Eggs hatch after a period of three weeks or longer. Some Charadriiformes, including most shorebirds species, have precocial chicks. These hatch at a fairly advanced stage of development, covered with down and able to move. Precocial chicks are usually able to leave the nest soon after they hatch. Others, such as most seabirds, have altricial chicks, which hatch at a less developed state. These hatch blind and without feathers, and usually stay in the nest for a longer period of time.