Ixobrychus exilis (Gmelin)
Dwarf Bittern, Little Bittern, Cory’s Bittern, Least Heron.
Breeder. Uncommon to fairly common during spring, summer, and fall in Gulf Coast region, but rare in winter. Uncommon to rare inland during spring, summer, and fall. HIGH CONSERVATION CONCERN.
Smallest heron (28-36 cm [14 in.]) (Palmer 1962). Head slightly crested; has a slender, straight, pointed bill, and a large buffy patch on proximal half of upper side of each wing. Sexes similar in size, although plumage is dichromatic; crown and back of male black, while those of female purple-chestnut and neck of female darkly streaked. Juvenal plumage similar to that of adult female, but crown paler and browner, and breast and throat browner and more heavily streaked. A rare darker morph, “Cory’s Bittern” occurs in which paler areas of typical plumage appear chestnut-colored. Young covered with long, soft, ochre-colored down above, and whiter beneath. Can be quite vocal with a varied repertoire of calls. Male’s advertisement call, most frequently heard in spring, is a dove-like cooing uh-uh-uh-uh-uh-oo-oo-oooo-oo-ooah. Females may respond with ticking calls. When alarmed, three calls may be uttered: a loud, shrieking quoh, a hissing hah, or cackling tut-tut-tut (Palmer 1962). Two subspecies proposed, the nominate subspecies (I. e. exilis) and the western subspecies (I. e. hesperis). Most authorities no longer recognize hesperis as a valid subspecies (Gibbs et al. 1992).
DISTRIBUTION: In western North America, breeds locally in southern Oregon, interior and southern coastal California, central Baja California, and southern coastal Sonora. Breeds throughout most of eastern North America from southern Manitoba and North Dakota east to coastal Maine, south to Florida, and west to Texas. Also found in the Greater Antilles, and regions of Central America such as Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, Panama, and elsewhere, especially Mexico. In South America, occurs in Colombia, Peru, and east of Andes from Venezuela and Guianas south to Argentina and Brazil. Winters in southern California, southern Texas, and northern Florida south through breeding distribution in South America (AOU 1998, Gibbs et al. 1992). In Alabama, considered a fairly common breeder on the coast, a local and uncommon breeder in Inland Coastal Plain, and a rare breeder in the Tennessee Valley (Jackson 2001a).
Prefers tall emergent vegetation in primarily freshwater marshes, but will use coastal brackish marshes and mangrove swamps. Marshes with scattered bushes or other woody growth seem to be selected and artificial wetlands are readily used. Habitats vary considerably throughout North America, but nesting usually occurs in dense, tall growths of emergent vegetation interspersed with some woody vegetation and open freshwater. Cattail, sedge, bulrush, or common reed frequently used (Weller 1961, Palmer 1962, Swift 1987). Often associated with cattail-vegetated edges along deep, open waters (Weller 1961), and nutrient-rich microhabitats. Wintering birds appear to occur most frequently in brackish and saline swamps and marshes (Palmer 1962), but little known about wintering habitats.
Insects, crustaceans, and small fish make up bulk of diet (Palmer 1962).
LIFE HISTORY AND ECOLOGY:
Return from southern wintering grounds to breed in April or early May. Usually solitary and secretive, but breeding colonies do occasionally form near abundant food sources (Weller 1961, Palmer 1962). Probably form seasonal, monogamous pair bonds. A platform nest of dried and living plant material is built over shallow water and four to five pale bluish eggs are laid. Both sexes incubate the eggs for 17 to 20 days. Semi-altricial young hatch asynchronously over a three-day period, are brooded for several days, and fledge after five to 15 days. Young fed regurgitated food by parents.
BASIS FOR STATUS CLASSIFICATION:
While widely distributed in North America, preferred habitats are disappearing at an alarming rate. Loss of wetlands poses the most significant threat. Palustrine emergent wetlands, including inland, freshwater, and brackish wetlands, are among the most threatened wildlife habitats in the United States, and more than two million hectares (five million acres) were lost between the mid-1950s and mid-1970s (Tiner 1984). In Alabama, loss of cattail marshes to development, sedimentation from agricultural operations, and spread of common reed has negatively impacted species. In addition, widespread use of agricultural and residential chemicals has probably impacted prey populations. The extent of impact is not well understood due to secretive nature and difficulty of detection during surveys.
C. Dwight Cooley