Breeding Ranges Shift Northward

By Michael Caduto

Vermont is at the southern boundary of the savannah sparrow’s summer breeding range. Predictions show that, as the climate warms, this species will breed farther north and disappear from Vermont.” Photo: Michael J. Caduto

Have you ever wished you could experience a bird’s sense of freedom while soaring beneath an azure sky, thrilling to the feel of wind in your feathers and the sight of Earth from on high? We watch our avian friends with a sense of envy and delight. Avid birdwatchers travel to great distances and heights in order to watch birds and track their movements. A rare species sighted outside of its normal range often leads to mass migrations among adoring fans of these avian rock stars.

We become especially concerned when birds behave in unexpected ways. Songbirds are feathered barometers—harbingers of changes in the environment. In recent years, species that normally breed in southern New England are building nests and raising broods in Vermont and New Hampshire. Although climate change is one cause, there are many other reasons.

“Some expansions of bird ranges have been taking place for a long time,” said Laura Erickson, author of nearly a dozen books about birds and former Science Editor for the Cornell Laboratory of Ornithology. “For instance, the increased use of bird feeders started expanding the cardinal’s range north decades ago, helping them to survive harsh winters. Cardinals eat weed seeds in winter, so the limit of their winter range corresponded with where snow was deep enough to cover the weed seeds.” Although winter bird feeding has been encouraging cardinals to move north since at least the 1950’s, the relatively moderate winter weather and diminishing snow cover of recent decades have also encouraged cardinals to expand their range.

Northern mockingbirds and tufted titmice are other well-known northward drifters. Erickson has observed that the nesting range of the beloved titmouse—with its outsized call of “Peter, Peter, Peter,” and tiny, cardinal-like crest—is shifting north, especially in New England. “They’re a bird of the beech/maple forest, so changes in forest composition to hardwood, along with more bird feeding, have contributed to their increase.”

Over time, field studies for the Breeding Bird Atlases in Vermont and New Hampshire have revealed dramatic northward shifts of breeding ranges. (In 1985 the Vermont Institute of Natural Science, which was then based in Woodstock, published the first such atlas in the U.S.) Trends show that the summer ranges of cardinals, titmice and mockingbirds continue to grow, along with those of the purple martin, orchard oriole, cerulean warbler and loggerhead shrike. Red-bellied woodpeckers only began appearing in southern Vermont during the mid 1990’s, but they now breed here and are visiting bird feeders more often. This is also true of Carolina wrens.

According to Erickson, “Carolina wrens are truly a non-migratory bird. After the nesting season, an individual used to die if it scattered too far north. Their range has been expanding because temperatures are moderating and they’ve shown more action at bird feeders. They’re also a bird of the hardwoods, and have responded to increases in hardwood forest habitat. Red-bellied Woodpeckers are also associated with hardwood trees. Some of our conifers are more prone to diseases as winters become more mild and habitat gradually changes to hardwoods.”

Although our changing climate has enabled many birds to expand their ranges into northern New England, it can also have an adverse impact on the birds that already live here. As the climate warms, habitat is gradually transformed. The spruce-fir forest of uplands and mountain slopes transitions into hardwoods. Birch, beech and maple forests grow into oak and hickory over time.

Along with these changes in habitat, some of our signature northern New England summer birds will likely decline, or disappear, including evening grosbeaks, winter wrens, bobolinks, red-breasted nuthatches, dark-eyed juncos and both yellow-rumped and black-throated green warblers. This list includes the state birds of both Vermont and New Hampshire—the hermit thrush and purple finch, respectively. Other, now-southern species will begin to appear and increase, like the blue grosbeak, dickissel, Carolina chickadee, white-eyed vireo, summer tanager and Kentucky warbler.

The onset of a milder climate can alter the ranges of birds for other reasons, including fewer instances of extreme cold spells that can kill birds outright, and changes in the life cycles of insects and plants in response to longer growing seasons. Hotter summers tend to amplify the harm caused by air and water pollution. Research has shown that warmer weather and increased rainfall will also decrease the supply of larvae that are eaten by black-throated blue warblers. This hurts the survival of adults and the young birds they are raising.

Some adaptable birds, like the black-capped chickadee, learn to alter the timing of their nesting behavior to allow for changes in the dates when the insects hatch that they normally feed to their young. Some migratory species, however, may arrive earlier in springtime and start nesting before the insect food they need for raising a brood is available.

Birds in extreme environments face an especially difficult struggle to adapt, like the handsome gray jay or “whiskey jack,” which generally lives in high, sub-alpine spruce forests. Explains Erickson; “Gray jays are scavengers that cache their food in the fall, such as carrion. They nest in February, but winter thaws have been spoiling their food when they most need it.” Other subalpine birds—like Bicknell’s thrush and the blackpoll warbler—could disappear altogether from this region.

In northern New England, and across the world, we are witnessing a landmark ecological era during which avian species will adapt and survive, move on, or perish. According to National Audubon, the ranges of half of the more than 300 species of North American birds studied have moved north by at least 35 miles in the past 40 years. For birds, as with humankind, change is the only constant on the horizon.

WHAT YOU CAN DO:

• The Audubon report called Survival by Degrees: 389 Bird Species on the Brink concluded that two-thirds of the continent’s birds risk extinction due to global warming. Visit Audubon’s “Bird and Climate Visualizer” to find out how climate change will impact birds in our area, and how you can help: https://www.audubon.org/climate/survivalbydegrees
• Urge your elected state and federal officials to be proactive in supporting and implementing solutions to climate change.
• Attend monthly films in the Climate Change & Sustainability film series, offered by Sustainable Woodstock and Pentangle Arts.
• https://pentanglearts.org/sustainable-woodstock/