Golden-crowned kinglet, photo by Jim Stewart
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. For context, 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.
One might ask why these adaptations confer any advantage to the kinglet. For a kinglet, or any bird, a rainstorm followed by freezing weather amounts to dangerous conditions. The issue of thermal insulation is a problem for birds generally, since most birds must face the elements, which is why we see about three quarters of bird species leave Wisconsin each winter. Those that stay are often able to modify their environment or seek shelter in some way—woodpeckers in a cavity or ruffed grouse burrowed into a heap of snow. Kinglet’s flight feathers shed water, and are arranged in such a way that might allow the kinglet to protect its downy feathers during a storm.
Golden-crowned kinglet, photo by Kelly Colgan Azar
Also, what exactly are kinglets eating? Bernd Heinrich set out into the Maine winter to find out answers to these questions. First, he obtained permits to collect shot kinglets and analyze their gizzard contents. What he found surprised him—caterpillars!
How were kinglets eating caterpillars in the dead of winter, and what species? Heinrich went around with graduate students and a sturdy pole, and whacked maples, hemlocks, and spruces, and they analyzed the contents that dropped out of the trees. They found numerous caterpillars, and after several unsuccessful attempts, reared a one-spotted variant moth, Hypagyrstis unipunctata, which was previously unknown to northern climates. Thus, it appears caterpillars fuel at least a large portion of the kinglet’s insatiable diet.
Photo by Arlene Koziol
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 Celsius.
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.
Two years ago 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 settling into Wisconsin in the past few weeks.
Written by Drew Harry, Faville Grove Sanctuary land steward
