range

Northern Parula

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The northern parula is a delightful spring treat in Wisconsin, as it skips along the canopy, headed to northern boreal and coniferous forests. This blue-gray bird, with a yellow belly and throat and a bejeweled necklace of blue gray and copper, looks to have arisen from the tropical forests of Central America, and does return to those forests to overwinter for over almost 8 months of the year.

Photo by Steve Guttman

Photo by Steve Guttman

Recent research indicates that northern parulas may not be keeping up with a changing climate. On their spring flights from Central America and the West Indies, the birds are falling behind leaf-out dates in North America. This asynchrony can have cascading impacts on the birds and their overall populations. A key to the migratory ecology of neotropical migrants is the correct timing of migration, yet as these birds follow the day length, northern climates are rapidly greening, and this leafing out of trees and shrubs brings a pulse of insects, including many caterpillar species. Missing this important pulse of resources could have significant implications for the conservation of the northern parulas.

Range maps of northern parulas show a distinctive gap roughly through the Midwest and portions of the Northeast. There are a number of possible explanations for this, though none very satisfying.

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One possibility is habitat loss in these areas; the northern parula needs rather extensive blocks of forest, and remaining forest tracts in southern Wisconsin are relatively small. Yet, the parula makes it into areas of northern Illinois and Indiana, which are intensively agricultural and only have small forest fragments.

Old Man’s Beard lichen, photo by Bob the Lomond

Old Man’s Beard lichen, photo by Bob the Lomond

Another possibility is that parulas have some ecological requirement that is unfulfilled in the upper Midwest. In many observed cases of nest building, northern parulas use Spanish moss in the south (actually a bromeliad) and old man’s beard lichen in northern Minnesota, Wisconsin, and Michigan. These wispy materials are ideal for constructing nests. It is possible that a decline of the old man’s beard lichen (an Usnea species) due to air pollution has also caused a decline in northern parulas.

Lichens offer astounding insights into the overall quality of an ecosystem. Research in the Pacific Northwest has shown lichens to be reliable bioindicators, or representative of ecosystem health. Lichens accrue pollutants throughout the year, showing no seasonality, and they are long-lived. Lacking roots, lichens depend on atmospheric and water sources for nutrients, which also contain contaminants. Dynamic cycles of moisture and drying can concentrate pollutants over the lichen tissues, cell walls, and organelles. These features make lichens sensitive to pollution. In addition, widespread ranges offer clues as to where more severe pollution may have reduced or eliminated populations of lichens.

Above, a density map of native epiphytic (plant growing on another plant, obtaining nutrients from air, rain, water, or debris) species in the United States roughly corresponds with the range of the northern parula.

Above, a density map of native epiphytic (plant growing on another plant, obtaining nutrients from air, rain, water, or debris) species in the United States roughly corresponds with the range of the northern parula.

All of this is to say, the northern parula has an interesting range map; a curious gap in the central United States likely has no clear explanation, but a number of theories take aim at reasons why.

While northern parulas do not breed in most of southern Wisconsin, you can find them right now and in the next few weeks as they move through woodlands where the oaks are just starting to leaf out. Just the other day I was watching a group of parulas flitting through a stand of aspen. I got an excellent look at one of the birds as it dropped down onto a shrub and swallowed a massive caterpillar. The bird sat still for a few seconds—an eternity for a parula—and then flew off again, likely on its way to a spruce or tamarack forest in northern Wisconsin.

Written by Drew Harry, Faville Grove Sanctuary land steward

Header photo by Dan Pancamo

Golden-crowned Kinglet

Photo by Kelly Colgan Azar

Photo by Kelly Colgan Azar

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.

Photo by Kelly Colgan Azar   

Photo by Kelly Colgan Azar
 

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.

Photo by Kelly Colgan Azar   

Photo by Kelly Colgan Azar
 

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