Cerulean Warbler (Dendroica cerulea)

Status: State Threatened (1989).

Occurrence: Uncommon migrant south and central, rare migrant north. Uncommon summer resident south and central, rare summer resident north. Southern Wisconsin north to a parabolic line extending from Eau Claire, south to Wisconsin Rapids and north to Green Bay. Robbins (1991) considers the summer range as the southern half of the state, with an increase in the west, north to St. Croix Falls and Sarona, and an increase in the east, north to Keshena, Peshtigo and Sturgeon Bay. Territorial males recorded in the mid 1990's north to Polk, Burnett, Oneida, and Marinette counties. A map outlining Pre-1977 and 1997 to Present Distribution is available.

Aid to ID: Adult male in breeding plumage is sky-blue above with faint dark streaks, and white below with a narrow black breast band and blue-gray streaking on the sides. Adult female is greenish above with a pale-yellowish stripe over the eye, and pale below with dully streaked sides. Both have two white wing bars.

Habitat: Mature mesic deciduous woodlands, including maple, basswood, and especially oak in both uplands and lowland or floodplain forests. Often found near small canopy openings in large continuous forest tracts; prefer medium and large tracts over small tracts (less than 40 acres).

Food Habits: Insectivorous. Diet includes bees, wasps, caterpillars, and weevils.

Natural History:

• Breeding: Clutch size: 3-5 (average: 4) white, cream-white, or green-white eggs speckled or blotched with purple and brown; laid from May to July. Incubation: 9-10 days by female. Young fledge 12 days after hatching.
• Nest: A shallow cup of neatly interwoven fine grasses, plant fibers, bark strips, weed stems, mosses, and lichens. The nest is lined with fine fibers and mosses and bound on the outside with spider silk. Placed 20-60 feet above the ground on a horizontal limb.

Management Considerations: Destruction of both wintering and breeding habitat through deforestation presents a large threat. Other limiting factors include forest fragmentation, contaminants, loss of key tree species to diseases, cowbird parasitism, and human disturbance. Protection of extensive mature forested tracts, especially mature floodplain habitats in Wisconsin and Minnesota will benefit this species and many other neotropical migrants as well.