Connecticut Warbler Oporornis agilis Scientific name definitions

Often highly elusive and retiring, the Connecticut Warbler is an uncommon and localized breeder in spruce–tamarack bogs, muskeg, mixed spruce–poplar forests, drier jack pine (Pinus banksiana) forests, and aspen–poplar woodlands across central Canada and south to northern portions of Minnesota, Wisconsin, and Michigan. It is reported to overwinter in humid forest undergrowth, forest edge, dry deciduous woodland, and dense deciduous scrub, up to 1,500 meters elevation, in Bolivia and southwestern Brazil, but its overwintering ecology and distribution are very poorly known.

The Connecticut Warbler is an original member of the genus Oporornis, which formerly included MacGillivray's Warbler (Geothlypis tolmiei), Mourning Warbler (Geothlypis philadelphia), and Kentucky Warbler (Geothlypis formosa). However, a recent revision of the taxonomy of the New World warblers (Parulidae) left the Connecticut Warbler as the sole member of the genus Oporornis and moved the three remaining species into the “yellowthroat” genus Geothlypis. Rather than being phylogenetically closest to its three former congeners, the sister species of Oporornis agilis is actually the enigmatic Semper's Warbler (Leucopeza semperi) of St. Lucia, a species that is possibly extinct. Together, these two species are in turn sister to Geothlypis.

Since being described by Alexander Wilson in 1812, the Connecticut Warbler has been the focus of little research. Its secretive behavior and habit of breeding and overwintering in remote areas have made it very difficult to study. Its nest was not discovered until 1883, and for decades, much of the information on breeding biology was provided by observations of a single nesting pair in Michigan. However, recent studies using new technologies have provided valuable details on the biology of this species. Geolocator data indicate that fall migrants perform a transoceanic flight from eastern North America to the Greater Antilles followed by a second flight across the Caribbean Sea to overwintering grounds in South America. The use of telemetry and digital video cameras placed at the nest have shown that males and females contribute to parental care in different ways. Incubation is only performed by the female, and while the male contributes to brooding, he assumes a primary role in feeding hatchlings and nest sanitation. Other recent research has contributed to a much better understanding of vocal behavior, with the first detailed studies of song finding extensive individual variation, both locally and across the breeding range.

The global population of the Connecticut Warbler is reported to be in decline. One study estimated that 60% of the breeding population was lost between 1970 and 2014 (see Population Status). Losses have been attributed to agricultural development, peat mining, and timber harvesting on the breeding grounds. Population trends could be exacerbated by continued habitat loss and climate change. For example, population models incorporating the effects of climate change have predicted that most of the breeding range in Alberta could be lost by the end of the 21^st century. The impacts of climate change on the boreal forests of North America may produce similar reductions in other parts of the breeding range.