The morning chorus of songbirds at Acadia National Park is losing some of its well-known voices.
New research suggests the park’s forests have grown quieter over the last half-century, in part because of a fast-warming climate.
The once common flute-like melody of the Swainson’s thrush is giving way to the car alarm calls of the red-breasted nuthatch. Some birds have left, like the bay-breasted warbler and the olive-sided flycatcher. The stretches of silence between calls and songs are increasing.
“It may not be noticeable to park visitors now, but that’s because they don’t know what it used to sound like,” said Gillian Audier, a 26-year-old researcher who spent last summer recording forest birds at Acadia. “But the historical record is clear: It used to be much louder.”
As a fellow at Schoodic Institute, Acadia’s research partner, Audier braved dew-soaked, tick-infested thickets to recreate the work of Ron Davis, who first cataloged these coastal woods as a graduate student in 1959.
Her findings were sobering. Audier heard fewer forest birds in 2025 than Davis did in 1959. Birds that were common then are less now. Even the zee-zee buzz of black-throated green warblers, the park’s most common bird, is heard three times less often, Audier concluded.
“It’s still so beautiful,” Audier said. “But it’s also less alive.”
Not that most people could tell. Because of “shifting baseline syndrome,” a phenomenon where a generation accepts a degraded environment as natural, a modern-day tourist may hear the loud, two-second trill of the male dark-eyed junco and assume the Acadian ecosystem is intact.
To visitors, the forest sounds lively. To those who know its history, like Audier, it sounds empty.
Climate change is a major reason for the new silence, Audier said. The cool waters of the Gulf of Maine act like a natural air conditioner for coastal forests, letting the cold-adapted red spruce and balsam fir grow at sea level instead of just on cold mountain peaks.
But the average surface temperature of the Gulf of Maine is rising at a rate nearly triple the global average, according to the Gulf of Maine Research Institute. That rapid warming is weakening the natural cooling effect, putting Maine’s cold-adapted coastal forests at risk.
Under current warming trends, Acadia National Park could see its average annual temperature increase as much as 8 degrees Fahrenheit by 2050, according to a 2024 report from the National Park Service.
A hotter Acadia isn’t directly harmful to most forest songbirds, Audier said. But that kind of heat creep can trigger insects and plants to hatch and bud too early for migratory birds or hatchlings to eat. When that kind of mismatch occurs, a population can eventually flicker out.
“I’ve learned the ecosystem exists beyond what I’m measuring,” Audier said.
Audier spent months learning the songs of 50 species until she knew each chirp and trill by ear.
On recording days, Audier’s pre-dawn ritual would begin at 4:30 a.m., racing to reach Davis’ 66-year-old testing sites before the birds that make up the energetic dawn choir would retreat from the midday heat. In total, she spent more than 45 hours in the woods.
She would use GPS and hand-drawn maps to locate Davis’ off-trail test sites. Once there, Audier would wait silently for the birds to get used to her, then log every song she heard in 5-minute intervals while walking the same path that Davis did.
If she didn’t recognize a song, she’d record it and ask the Institute to help her identify the bird.
Three of the five songbirds Davis heard most often didn’t crack Audier’s top five list: the yellow-rumped warbler, the Swainson’s thrush and the magnolia warbler. Audier did hear them, but not often, suggesting their numbers had dropped over that time period.
That quieting matches what is happening in other forests where historical birding records exist, Audier said. It’s not surprising. A landmark 2019 study conducted by Cornell University found North America has lost 1 in 4 adult birds since 1970.
Even a quiet forest offered Audier glimpses of the beauty that inspired Davis a half-century ago. Ironically, she only saw about 10% of the birds she heard, either because they preferred to chatter from the tree tops or because she had her head buried in her logbook.
She would find sea urchin shells dropped by gulls on the forest floor. The blanket of deep green moss silenced her footsteps, allowing her to hear the chugging of nearby lobster boats, clanging of the navigational buoys and the high-pitched notes of the golden-crowned kinglets.
Audier’s bird census is the second chapter of a larger story. In 2024, researcher Camilla Seirup published an update to Davis’ 1959 tree inventory. Seirup found Acadia’s dominant tree, the long-lived red spruce, is more resilient than climate models had predicted.
But Audier’s findings suggest Acadia’s songbirds may be more vulnerable to a warming climate.
When Audier met Davis, now in his 90s, they connected over their shared love for this unusual cold-adapted, sea-level forest. Davis told her he felt a “sense of delight” that a new generation of scientists was using his work as a foundation to measure the impact of climate change.
Audier’s fellowship at Schoodic Institute is over. She now works as a shorebird tech monitoring piping plovers and least terns at Crane Beach in Massachusetts. But she thinks about her time in Acadia often, she said. A research paper on her findings is in the works.
This story was originally published by the Maine Trust for Local News. Penny Overton can be reached at [email protected].
