Kentucky Warbler (Oporornis formosus)

Status: State Threatened (1989).

Occurrence: Uncommon migrant southwest; rare migrant southeast. Uncommon summer resident southwest. Found largely in the southwestern corner of Wisconsin. Their range extends from Grant County to Pepin County along the Mississippi River, and east through Sauk County and Dane County along the Wisconsin River. Commonly found in early summer in parts of Wyalusing State Park, Tiffany Bottoms, and in the Baraboo Hills in Sauk County. A map outlining Pre-1977 and 1997 to Present Distribution is available.

Aid to ID: Distinguishing characteristics include a black mustache and a yellow eye ring. In young birds, mustache is not prominent.

Habitat: In Wisconsin, Kentucky Warblers nest in shrubby woodlands on hillsides and in brush floodplains, especially near white oak swamps. Found particularly in areas with a dense understory near the base of surrounding bluffs. Occur along major rivers, such as the Mississippi, lower Chippewa, and Wisconsin, and in ravines and hillsides of streams that feed into these rivers. Prefers moist ravines and bottom lands.

Food Habits: Diet includes grubs, plant lice, spiders, caterpillars, and other insect larvae.

Natural History:

Breeding: Clutch size: 3-6 white or cream-white eggs speckled or blotched with browns; laid from May to June. Incubation: 12-13 days. Young fledge 8-10 days after hatching. Females will fake injury to draw predators away from the nest.
Nest: Bulky cup of leaves, grasses, weed stems, and twigs lined with rootlets and hair placed on or just above the ground.

Management Considerations: This species was rare in Wisconsin in the nineteenth century. Nesting has not been reported from any eastern counties, and all eastern sightings have been considered nonresident. The necessity of a dense understory may limit the Kentucky warbler. This species builds its nest on or near the ground. Preservation of large continuous blocks of deciduous forests in the Baraboo Hills and along the major river valleys of southwestern Wisconsin will benefit the species.