Blackburnian Warbler. Credit: Courtesy of Bob Duchesne

Now that summer is in full swing, many of us are hiking, biking, paddling and mountain climbing — you know, all the things I used to do. For those who still stumble up mountains, there is something you should know: The habitat changes as you go uphill, and thus, so do the bird species you’ll encounter along the way.

Here’s the magic formula: 1,000 feet of elevation gain is the habitat equivalent of moving 300 miles farther north. That means the birds you find near the bottom of Maine’s mountains are typical of the birds found throughout the nearby forest.

But the birds near the summit are more typical of those that dominate the landscape hundreds of miles into Canada’s boreal forest.

Let’s pick a few mountains as examples. Perhaps you’re familiar with Mt. Blue near Farmington, Big Moose near Greenville, Big Spencer on the northside of Moosehead Lake or any of a dozen other peaks that stretch to 3,000 feet or higher.

Now let’s pick a bird family — let’s say, thrushes. The same phenomenon happens with each mountain.

Bicknell’s thrush. Credit: Courtesy of Bob Duchesne

Typically, the base of the mountain is mostly deciduous, with lots of oaks, maples, birches and beeches. As you ascend, the microclimate becomes cooler and damper. The oaks disappear and the maples dwindle. Hemlocks replace pines. Yellow birch and balsam fir take over from the beeches. Closer to the summit, spruce begins to dominate — at first tall, but later stunted, dense and impenetrable.

At the bottom of the mountain, wood thrushes are possible, especially around the more southerly Maine peaks. Hermit thrushes and veeries are found everywhere. After a half-hour of climbing, the early thrushes disappear, and Swainson’s thrushes begin to take over. The sound of the forest literally changes.

Above 2,800 feet, the forest becomes krummholz — a German word for stunted, deformed spruce. This is the realm of the rarely seen Bicknell’s thrush.

The same thing happens with warblers. The base of the mountain is dominated by birds that prefer mature deciduous trees. Ovenbirds and northern parulas are abundant. Blackburnian warblers, as well as black-throated green and black-throated blue warblers, are common. As you climb, you might notice that the heartier yellow-rumped warblers become more prevalent.

About halfway up the mountain, there is often an area where the hardwoods yield to spruces almost entirely. The remnant birches, beeches and firs on the edge of this zone are scrawny. This is the kind of shorter tree growth that sun-loving warblers desire, and there’s usually a bunch of black-and-white warblers, Nashville warblers and American redstarts in this region. Once you’re deep into the spruces at the higher altitudes, blackpolls and bay-breasted warblers take over.

Pick any family of birds. Scarlet tanagers and rose-breasted grosbeaks tend to be toward the bottom of the mountain, joined by an abundance of red-eyed vireos. Blue-headed vireos tend to prefer the zone just above them. Most of the flycatcher family is near the bottom, but yellow-bellied flycatchers prefer the summits.

One bird demonstrates the most dramatic example that elevation equals latitude. The American pipit is a tundra-loving bird. Its normal breeding range begins in the upper reaches of Quebec and Labrador, extending northward above the Arctic Circle. But there are two places in New England where they nest: the tablelands atop Katahdin, and the summit of Mt. Washington. Tundra habitat prevails on each.

The good news is, you don’t actually have to climb a mountain to see this effect.

There’s a noticeable elevation change just driving through Baxter State Park. After you enter the southern gate, the song of hermit thrushes is ever-present. Just beyond Abol Pond, about four miles north, the road winds uphill, and Swainson’s thrushes become more common, hermit thrushes less. Bay-breasted warblers and blackpolls begin to appear north of Katahdin Stream Campground. The road gains elevation again north of Nesowadnehunk Fields Campground, and the area becomes dominated by spruce, where these northern warblers become more common.

The other good news is that many of these boreal forest species are also found at lower altitudes, primarily in northern and Down East Maine. Wherever the forest is cool and damp, pockets of spruce-filled habitat flourish. Streams and bogs in the north woods are often surrounded by spruce stands that can go on for miles. Some of them are regenerating from earlier clear-cuts, producing patches of low, dense spruce similar to the krummholz found on mountaintops.

The nice thing about mountain birding is that I now have more excuses to stop and catch my breath.

Watch more:

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 mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.