The scarlet tanager is one of the many migratory birds that nest in Maine, and may be affected by climate change. Credit: Courtesy of Bob Duchesne

I don’t know if this is good news or bad news, but it’s certainly news. The ink is barely dry on a new scientific report about spring bird migration. Birds are returning to their nesting grounds earlier now, due to climate change. The good news: some species are adapting. The bad news: they are probably not adapting fast enough.

This latest study looked at 24 years of weather radar data, which is able to follow migration patterns across the entire continent. A team of scientists from Colorado State University, the Cornell Lab of Ornithology and the University of Massachusetts documented that birds are now passing migration checkpoints earlier than they did 20 years ago. Furthermore, the biggest changes appear to be happening in areas that are warming fastest.

It is no surprise that birds would adapt. Migration itself is probably the result of adaptation to prehistoric climate changes. Birds go wherever they can find food. Many of the birds we enjoy in Maine are happier to see our bug season than we are. But 20 years is a disturbingly short timespan for any species to adapt to abrupt climate change.

[Also read: Maine is seeing fewer winter birds. Where are they?]

Phenology is the study of nature’s timing. Specific to Maine, when do our lakes thaw? When do our trees leaf out? When do the black flies torment? How did mayflies and June bugs get their names?

Phenology is critical to birds. For thousands of years, they’ve instinctively timed their migrations to arrive in North America when the banquet table was full. While flitting around the treetops in Panama, birds have no idea what conditions are like back home in their nesting areas. They don’t know that milder winters are leading to earlier plant blossoming and premature insect hatchings. They don’t know that the changing climate requires them to migrate earlier.

Instead, they find out the hard way. Birds arriving too early risk starvation. Conversely, birds arriving too late miss out on prime nesting sites and mating opportunities. Timing is everything. When the climate is warming, evolution favors the early-arrivers. When the climate is cooling, evolution favors the late-comers. Thus, species adapt slowly.

Credit: Courtesy of Bob Duchesne

Migrating birds may not be keeping up with the rapidity of climate change in our era. Another headline-grabbing study, released in mid-2019, documented the disappearance of 1.9 billion birds from North America over the last 50 years. Many factors are contributing to this alarming decline, but climate change is clearly one of them. Since humans began recording annual temperatures, 17 of the 18 hottest years on record happened during the first 18 years of this century, according to both NASA and NOAA.

None of this is particularly surprising. The latest data confirms what the old data already showed. The U.S. Geological Survey operates the North American Bird Phenology Program. It houses a data set of six million historical observations, mostly hand-written, dating back to the 1880s. As you can imagine, many old-time farmers, loggers and naturalists kept detailed records of when the timing of natural events occurred.

An alert reader sent me an even more bizarre study last week. A professor at the University of Michigan has published evidence that our birds are actually shrinking in physical size. For 40 years, researchers and volunteers have collected dead birds that collided with Chicago skyscrapers. Recently, those 70,716 specimens were measured. The results were correlated across the 52 North American migratory species collected. On average, the later birds had shrunk by 2.4 percent. This quirky study also proved that biologists need to get a life.

The shrinkage of birds in a warmer climate is consistent with something called Bergmann’s rule. It’s a principle, described in 1847 by German biologist Carl Bergmann that species tend to be larger in northern climates. Well-travelled birders know that eagles and blue jays in Maine are considerably larger than eagles and blue jays in Florida. Alaskan eagles are bigger than Maine’s. So are Alaskan moose.

[Also read: Birds that can’t stand the heat of a warming world grow smaller]

Phenology studies are also happening close to home. It is one of the principal research projects conducted by Schoodic Institute in Winter Harbor. If you walk around Schoodic Point or Petit Manan National Wildlife Refuge, you might see bushes adorned with tags. These shrubs are monitored for fruit ripening and food availability to birds. On top of Cadillac Mountain, test plots are assessing what southern plant species might allow our future landscape to nourish wildlife, once the climate becomes too warm for current plant species.

Politicians need no longer debate when climate change will arrive. It’s already here.

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at He can be reached at

Bob Duchesne, Good Birding

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at He can be reached at