For most people in the Lower 48, the colorful Evening Grosbeak is considered a rare treat at feeders during the winter months. But in the forested areas along the U.S.-Canada border, this big-billed finch is common, brightening backyards from Portland, Oregon, to Portland, Maine.
That may be changing, according to the latest update of the Wisconsin Breeding Bird Atlas, a 20-year community science effort to survey breeding birds in the state, published in the fall. Two decades ago, Evening Grosbeaks nested throughout the top half of Wisconsin; now they’re restricted to the far northern areas, suggesting a decline in their U.S. populations. And many other species, particularly those that thrive in forest habitats, also appear to be shifting their ranges northward into Canada—a pattern predicted by climate change models as global temperatures rise.
From 2015 to 2019, thousands of volunteers scoured the Badger State for breeding birds, repeating the effort of the first Wisconsin Breeding Bird Atlas, which was conducted over the five-year period from 1995 to 2000. A comparison of the data from the two atlases points to substantial changes in Wisconsin’s bird populations over the past two decades. There has been an exodus of cold weather-loving birds, like the Evening Grosbeak and the White-winged Crossbill, as well as the arrival of southern species new to Wisconsin, like the Mississippi Kite and the Yellow-throated Warbler. While habitat loss could be responsible for some of the declines, experts point to a warming climate as the main cause behind these dramatic shifts.
The atlas is based in a single state, however the observations represent broader trends seen across the country, says Brooke Bateman, senior climate scientist at the National Audubon Society, who was not involved with the effort. Wisconsin hosts a wide variety of habitats, from boreal forests and prairies to growing urban environments. It’s also positioned in the Great Lakes basin, an area already seeing significant warming from climate change. “It’s a unique place given its geography right at the border of Canada,” Bateman says. “It shows a pattern that’s starting to emerge that could potentially be much worse with climate change.”
Both the modern atlas and its predecessor were based on volunteer birders’ observations across hundreds of ‘atlas blocks’—regions measuring roughly nine square miles apiece scattered across the state. Unlike other surveys like Audubon’s Christmas Bird Count, the atlases sought to determine which birds are breeding in Wisconsin, not simply which ones were present. This required volunteers to watch for particular breeding behaviors, like feeding young or carrying nesting materials.
Keith Merkel is one of the volunteers who identified birds for the atlas, and he worked on the last one, too. Twenty years ago, Merkel was an atlas coordinator, summarizing volunteer birders’ observations as well as doing some surveys himself. Back then, volunteers tallied their findings on 11” x 17” sheets of paper and submitted them to coordinators by mail. Merkel then wrote letters back to participants who had made unusual sightings, waiting weeks or months to hear more detailed observations. The recent atlas, by contrast, used the popular birding app eBird for entering data: All unusual sightings were flagged automatically, and atlas data became available to everyone as soon as it was entered.
This year, Merkel spotted an Orchard Oriole for the first time—a species identified in nearly three times the number of atlas blocks as it was in the 1995-2000 survey. This small bird, identifiable by its rust-orange belly, black head, and musical warble, usually favors semi-open areas in the South and Midwest. “That was one that really stuck out, that I’ve never seen in this part of Wisconsin ever before,” he says. Merkel lives in nearly the exact center of the state. “They’re found more frequently in southern Wisconsin, but around here I had never seen one” until this year, he continues. “They’re indicators that things are changing in the environment.”
This small oriole wasn’t alone in shifting its range northward. Over the past five years, participants identified 13 species not seen in the first atlas, including more southerly species like the Blue Grosbeak, Mississippi Kite, Yellow-throated Warbler, and White-eyed Vireo. “One very striking result is how many more individuals of species with more southern U.S.-centered breeding ranges are in Wisconsin, compared with in the first atlasing effort,” says Anna Pidgeon, an avian ecologist at the University of Wisconsin who was not involved in the Atlas survey.
Birds aren’t only moving into the state; they’re also moving out. Birds that live in the boreal forests seem to be shifting north, abandoning Wisconsin territory and heading into Canada. One of these is the Boreal Chickadee, a specialty of these cold northern forests. “Twenty-plus years ago we were recording Boreal Chickadees pretty frequently,” Merkel says. “I’ve not seen one now for six or seven years, and didn’t see any during the atlas when I was in the same areas I used to be in years ago.”
Some of the most-depleted Wisconsin populations have been those of the Evening Grosbeak, White-winged Crossbill, and Connecticut Warbler. These species were observed in the northern portion of Wisconsin 20 years ago; in contrast, the few modern sightings are concentrated along the state’s northern border. “It is sad to see how species that require boreal habitat . . . have contracted in the number of blocks occupied, compared to the first atlas,” Pidgeon says. This trend is predicted in Audubon’s recent climate change report Survival By Degrees, which found that nearly all boreal forest species will be highly vulnerable to losing habitat to climate change by the end of the century; it projected that they'd respond by shifting their ranges north or potentially going localy extinct. These birds include many neotropical migrants, like colorful warblers, which nest in the boreal forest in summer.
“The boreal birds are the ones that are going to anticipate quite a lot of changes in the future, and they’re probably already experiencing changes from climate change,” Bateman says. “That will continue if we don’t do anything.”
Wisconsin is not alone in its mission to document the long-term changes in its bird populations. The second Maine bird atlas is currently underway and will be completed in 2022, providing detailed insights into changes since the state’s first survey in 1978–1983. Rhode Island is in the process of analyzing the data from its second atlas, which concluded this summer, and New York plans to embark on its third atlas next year. Along with providing invaluable population data, these surveys engage birders, naturalists, and amateur scientists in conservation efforts.
“There’s new behaviors that you’ll see while atlasing because you’re slowing down, you’re really being patient and watching very carefully what they’re doing,” Merkel says. “It’s a really great way to get to know birds better, even birds you think you know pretty well.”