Least Bittern (GTM Research Reserve Bird Guide)

Least Bittern

Ixobrychus exilis

Summary ⁶

The Least Bittern (Ixobrychus exilis) is a small wading bird, the smallest heron found in the Americas.

Taxon biology ⁷

The Least Bittern (Ixobrychus exilis) is the smallest member of the heron family, measuring 28-36 cm (11-14 in), weighing around 80 g, and with a wingspan of 43 cm (17 in). Their contrasting color patterns are diagnostic field patterns. The crown, back, and tail are a vivid greenish black. The neck, sides, and underparts are brown and white. Wings are chestnut with conspicuous, contrasting, pale patches. The head is slightly crested, the bill is thin and yellow, and the iris is yellow. (Gibbs et al. 1992). Bitterns have a laterally compressed trunk, short legs, short outer toes, and long, curved toenails that enable them to travel through and grasp the dense, emergent vegetation (NatureServe 2001). Legs are green on front, yellow behind; soles of feet are yellow. Pale, highly visible lines border scapular feathers. Sexes are similar in size, but plumage is dimorphic. The crown and back of the female is purple- chestnut; those of the male are black. The neck of the female is darkly streaked. Juvenile plumage is like that of the adult female but the juvenile’s crown is paler and browner; breast and throat is browner with heavier streaking. In a rare, darker morph, known as Cory’s Least Bittern, the pale areas of the typical plumage appear chestnut colored. (Gibbs et al. 1992).

Ixobrychus exilis migrates between temperate breeding grounds and temperate and subtropical wintering grounds. Migrants leave breeding grounds late August through September; few birds found north of Gulf States past mid-October. They return early April to late May, depending on latitude. They usually clamber through dense vegetation. Often moving deliberately from stalk to stalk, grasping vegetation with their toes, but they can run quickly, hop nimbly, and burrow rodentlike through vegetation. They seemingly fly weakly; flutter short distances when flushed, legs dangling, and drop quickly back into vegetation. (Gibbs et al. 1992).

Least Bitterns are quite vocal, with a varied repertoire of calls. Males utter a dovelike cooing, frequently heard in spring, which is thought to advertise their presence. Females reported to respond with ticking calls (Hancock and Kushlan 1984, in Gibbs et al. 1992). A gack-gack call commonly given from nest (Weller 1961, in Gibbs et al. 1992). When alarmed, a loud, shrieking quoh, a hissing hah, a tut-tut-tut, or a cackle may be expressed (Palmer 1962, Hancock and Kushlan 1984, Swift et al. 1988, in Gibbs et al 1992). Ank-ank call given when flushed from marsh (Weller 1961, in Gibbs et al. 1992). Defensive posture and interactions between mates may be accompanied by a call of gra-a-a (Weller 1961, in Gibbs et al. 1992). They are vocal in early morning, and perhaps more vocal at dawn than dusk (Swift et al. 1988, in Gibbs et al. 1992), but they are generally silent at midday and in the afternoon.

They generally consume small fish, and insects.