Kirtland’s Warbler

Life History

The endangered Kirtland’s warbler is one of the rarest members of the wood warbler (Parulidae) family. It is a bird of unusual interest for many reasons. It nests in just a few counties in Michigan’s northern Lower and Upper peninsulas, in Wisconsin and the province of Ontario and, currently, nowhere else on Earth. Its nests generally are concealed in mixed vegetation of grasses and shrubs below the living branches of five to 20 year old jack pine (Pinus banksiana) forests. The male Kirtland’s warblers’ summer plumage is composed of a distinctive bright yellow colored breast streaked in black and bluish gray back feathers, a dark mask over its face with white eye rings, and bobbing tail. The female’s plumage coloration is less bright; her facial area is devoid of a mask. Overall length of the bird is less than six inches.

Because of its restricted home range and unique habitat requirements, the Kirtland’s warbler probably has always been a rare bird. Did you know that the warbler management area consists of 125 separate tracts, totaling 6,684 acres, located throughout eight counties in the northern Lower Peninsula of Michigan? AND the largest concentration of the KW in MI is in IOSCO county?

It was not until 1903 that Norman A. Wood discovered the first nest in Oscoda County in northern lower Michigan. Until 1996, all nests were found within 60 miles of this site. Since then, a small number of nests have been found each year in Michigan’s Upper Peninsula. Nesting also has occurred in Wisconsin and the province of Ontario.

The diet of the warbler includes many different insect species at various developmental stages, including caterpillars, butterflies, moths, flies, grasshoppers, as well as ripe blueberries, when in season.

Breeding
Male Kirtland’s warblers arrive back in Michigan from the Bahamas between May 3 and May 20, a few days ahead of the females. The males establish and defend territories and then court the females when they arrive.

The Kirtland’s warbler has very restrictive habitat requirements. In addition to being ground nesters, Kirtland’s warblers prefer jack pine stands over 80 acres in size. Those stands, which are most suitable for breeding, are characterized by having dense clumps of trees interspersed with numerous small, grassy openings, sedges, ferns, and low shrubs. The birds nest on the ground under the living branches of the small trees. Jack pine stands are used for nesting when trees are about five feet high or about five to eight years of age. Nesting continues in these stands until the lower branches of the trees start dying, or when the trees reach a height of 16 to 20 feet (about 16 to 20 years of age). A breeding pair of warblers usually requires about six to ten acres for their nesting territory, although as little as 1.5 acres may be adequate under optimal conditions.