The Golden-crowned Kinglet, an active little bird weighing in at six ounces, seems an unlikely resident of the boreal forests of the north. The bird will even overwinter as far north as Alaska and Nova Scotia, and small numbers spend the winter in Wisconsin.
To accomplish this, the kinglet employs a number of adaptations that are advantageous in cold climates. First, the bird's feathers comprise about 8% of its body weight, which helps with insulation. That's about the same percentage of insulation that an arctic explorer might wear. Second, the bird expends almost 100% of its energy budget towards foraging during the winter months. Staying active and maintaining caloric needs helps the golden-crowned kinglet to maintain its internal body temperature of 110 degrees. Third, flocks of birds will group together at night, finding refuge in wind-breaking conifers, and huddling together for warmth. These kinglets are also known to hop into squirrel nests in trees as an added measure of insulation.
A rare winter resident in Wisconsin, about 250 golden-crowned kinglets are seen during the Christmas Bird Counts in Wisconsin each year. According to research from UW-Madison, contiguous patches of upland forested habitat, or forested habitat near urban areas, may assist the thermal capacity of birds like kinglets to withstand cold temperatures, as the birds can experience die offs at -40 degrees Fahrenheit.
Last year at Faville Grove we saw about a half dozen golden-crowned kinglets during the Birdathon on May 14. Typically golden-crowned kinglets will have migrated through by then, as they're early spring, late fall migrants—with the last of the birds likely moving through in the past week here at Faville Grove.
However, golden-crowned kinglets have experienced range expansions over past few decades, and breeders can be found in spruce plantations in Pennsylvania, Ohio, and Maryland. In Wisconsin, the second Breeding Bird Atlas has confirmed golden-crowned kinglets in the southern Kettle Moraine in Waukesha County conifer plantations, very disjunct from their typical breeding range in northern Wisconsin. It is possible that there are breeders in Jefferson County tamarack swamps, which once covered about 20% of the county, and which are incredibly difficult to access when the ground is not frozen.
Golden-crowned kinglets have a steady population continent-wide and in Wisconsin, and throughout the eastern US they have experienced population increases and range expansions into the aforementioned areas.
Written by Drew Harry, Faville Grove Sanctuary land steward