I’m in Pittsburgh, watching birds at a feeder. My friend’s back porch is fluttering with northern cardinals, tufted titmice, red-bellied woodpeckers, and Carolina wrens. That may seem irrelevant to Maine birders, but at this moment I have a front row seat to watch range expansion. These birds did not formerly occur in Maine. But they do now. Southern birds are marching north.
It would be easy to blame climate change for the northward expansion of southern birds, but there are other causes, too. These four species are comfortable around people. As suburban sprawl and backyard bird-feeding expands, so does the range of birds that tolerate human-induced changes to the environment.
It’s also normal for the ranges of birds to expand and contract. Red-bellied woodpeckers have a long history of range expansion. On the other hand, red-headed woodpeckers share much of the same historic range, but they are disappearing rapidly. Fossil records show that red-headed woodpeckers have been around for 2 million years, but they’ve declined by 70 percent since 1966. The change is partly due to a decline in nut-producing trees in American forests, plus our tendency to remove dead snags from woodlots.
But, as I sit watching these feeders, looking for evidence that climate change affects the range of birds, here comes Exhibit A. A Carolina chickadee has grabbed a sunflower seed, and flitted back to a nearby bough. Until this moment, it’s been all black-capped chickadees coming to the porch this morning.
There is a narrow band of overlap between these two species, and at this moment, I’m in it. This band stretches from eastern Kansas to northern New Jersey, and dips down the mountaintops of Appalachia all the way to Georgia. Carolina chickadees are southern birds. Black-capped chickadees are northerners. Where the temperature is more suitable for one species, it will outcompete the other. The zone where the two species co-exist is therefore very narrow.
And here’s the thing: That zone of overlap is moving north as the climate warms. Nowhere is that more apparent than right here in western Pennsylvania. That’s because Pennsylvania recently completed its second atlas of breeding birds, and the change has been thoroughly documented and mapped.
From 2004 to 2009, experts and volunteers fanned out across the state and recorded the location and behavior of every bird they could find. The results were then compared to the first atlas, which had been completed two decades earlier. Researchers confirmed that the overlap zone was moving northward at the average rate of 1 kilometer per year. Furthermore, Carolina chickadees were moving into survey areas formerly occupied only by black-capped chickadees at an accelerating rate. The number of invaded census blocks had increased 85 percent in just 20 years.
Maine has its own chickadee overlap. The northern forest is home to boreal chickadees, which are similar to black-capped chickadees, except that they are brown where they should be black. Black-capped chickadees are found statewide, whereas boreal chickadees are confined to spruce-fir habitat. Boreal chickadees completely replace the black-capped chickadee in northern Canada.
Anecdotally, I’ve watched the range of boreal chickadees in Maine recede northward. Twenty-five years ago, I observed them on Vinalhaven. Twenty years ago, they were easy enough to find in Stonington. It’s now been a decade since I’ve seen one there. I have favorite spots in Jonesboro and Roque Bluffs where they used to be automatic. It’s now been five years since I’ve found one in either spot. It’s been four years since I’ve seen one in Moosehorn National Wildlife Refuge in Edmunds.
Soon, we may have better scientific information. Maine is about to start its own second atlas of birds. We’re way overdue. It’s been more than 30 years since the first. Maine’s Department of Inland Fisheries and Wildlife leads the effort, assisted by hundreds of volunteer citizen-scientists statewide. You’ll be hearing more about this effort in the coming year.
Maine’s second atlas can’t come soon enough. Birds are a good indicator of what is going on in the environment. Losses in wetlands and grasslands are quickly documented by a decrease in the number and location of birds using those habitats. Nowhere is this more important than in Maine’s working forest. Not only have there been changes in our forestry practices since the last atlas, but factors such as spruce budworm and warming temperatures affect the range of birds.
If you want to know what’s going right and wrong, sometimes the fastest and cheapest way to find out is to ask the birds.
Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.