The Connecticut Warbler is a shy, retiring wood-warbler that breeds in spruce–tamarack bogs, muskeg, poplar woodlands and moist deciduous forests in northern Minnesota, Wisconsin, Michigan, and central Canada. It overwinters in northern South America in various habitats, but its distribution on the wintering grounds is poorly known. Alexander Wilson first described this species in 1812 and named it after the state of Connecticut, where he collected the first specimen, a fall migrant. The common name is something of a misnomer, however, because the species does not breed in Connecticut, nor is it a common migrant there.
An original member of the genus Oporornis—along with the MacGillivray's (O. tolmiei), Mourning (O. philadelphia), and Kentucky (O. formosus) warblers—the Connecticut Warbler is the most similar morphologically and ecologically to the first two species. The Connecticut, MacGillivray's, and Mourning warblers all breed in boreal forest, inhabiting similar strata in the forest and feeding and nesting on or near the ground. In other ways, however, they differ ecologically: Mourning and MacGillivray's warblers tend to breed in younger, disturbed second growth. Phylogenetically, however, these species differ significantly. A recent revision of the taxonomy of the Parulidae leaves the Connecticut Warbler as sole member of the genus Oporornis and lumps the other three species into the “yellowthroat” genus Geothlypis (Lovette et al. 2010).
The Connecticut Warbler was poorly known at the turn of the twentieth century and remains so today. Its nest, for example, was not discovered until 1883, almost 70 years after the species was first described. Its secretive behavior and preference for breeding habitat in remote areas with abundant insect life has made it very difficult to study. Much of what we know about this species was provided by observations of one nesting pair in Michigan (Walkinshaw and Dyer 1961). The most recent scientific papers have focused on distribution records, or its inclusion in broader studies of population trends and human impact on breeding habitat in the boreal forest (Sodhi and Paszkowski 1995b). There are still no rigorous, experimental studies of its general biology from the breeding or overwintering ranges.