Sheathbills: Chionidae

Sheathbills are monogamous (muh-NAH-guh-mus), a single male mates with a single female during the breeding season. Sheathbill pairs are territorial, and defend nesting and feeding areas within seabird colonies from other pairs of sheathbills. Territorial disputes are resolved by calling, displays, chases, and sometimes, actual battles.

The timing of the breeding season varies among populations of sheathbills, since breeding usually occurs whenever local seabirds are breeding. This strategy allows for plentiful food resources to be available when sheathbill chicks hatch. Females lay one to three eggs at a time, usually in November or December. Eggs are laid in crude nests built from feathers, bones, shells, rocks, and plant material. Nests are usually built in small caves or cracks, usually in rocky areas. However, some sheathbills will nest in the abandoned burrows of other species. Sheathbill eggs are white, flecked with brown or gray, and somewhat pear-shaped. Chicks hatch after twenty-eight to thirty-two days, and are partially covered with feathers when they hatch. Unlike the parents, chicks are brownish in color. Chicks stay near the nest for one to three weeks after hatching and are fed by their parents. The primary cause of death for chicks is starvation, although some chicks are also eaten by predators, animals that hunt them for food.