Least bittern

Appearance

The least bittern is one of the smallest herons in the world, with perhaps only the dwarf bittern and the black-backed bittern averaging smaller in length. It can measure from 28 to 36 cm in length, and the wingspan ranges from 41 to 46 cm. Body mass is from 51 to 102 g, with most least bitterns weighing between 73 and 95 g, making this perhaps the lightest of all herons. A recent manual of avian body masses cites another species in this genus, the stripe-backed bittern, as having a mean body mass slightly lower than the least bittern, which is credited with a mean mass of 86.3 g.

The bird's underparts and throat are white with light brown streaks. Its face and the sides of the neck are light brown; it has yellow eyes and a yellow bill. The adult male is glossy greenish-black on the back and crown; the adult female is glossy brown on these parts. They show light brown parts on the wings in flight.

Status

The bird has a large range and a large total population, and the International Union for Conservation of Nature has assessed its conservation status as being of "Least Concern". The least bittern is protected under the Migratory Bird Treaty Act of 1918.

Behavior

The least bittern is an elusive bird. They spend much time straddling reeds. When alarmed, the least bittern freezes in place with its bill pointing up, turns its front and both eyes toward the source of alarm, and sometimes sways to resemble wind-blown marsh vegetation. This is perhaps a predator-avoidance behaviour, since its small size makes the bittern vulnerable to many potential predators. Thanks to its habit of perching among the reeds, the least bittern can feed from the surface of water that would be too deep for the wading strategy of other herons. The least bittern and much larger and different-looking American bittern often occupy the same wetlands but may have relatively little interaction because of differences in foraging habits, preferred prey, and timing of breeding cycles. The least bittern arrives on its breeding grounds about a month after the American bittern and leaves one or two months earlier. John James Audubon noted that a young captive least bittern was able to walk with ease between two books standing 4 cm apart. When dead, the bird's body measured 5.7 cm across, indicating that it could compress its breadth to an extraordinary degree.

Evolution

These birds nest in large marshes with dense vegetation from southern Canada to northern Argentina. The nest is a well-concealed platform built from cattails and other marsh vegetation. The female lays four or five eggs, in extreme cases from two to seven. The eggs are pale blue or green. Both parents feed the young by regurgitating food. A second brood is often produced in a season.

These birds migrate from the northern parts of their range in winter for the southernmost coasts of the United States and areas further south, travelling at night.

They mainly eat fish, frogs, crustaceans and insects, which they capture with quick jabs of their bill while climbing through marsh plants.

The numbers of these birds have declined in some areas due to loss of habitat. They are still fairly common but are more often heard than seen. They prefer to escape on foot and hide than to take flight. These birds make cooing and clucking sounds, usually in early morning or near dusk.