Every 1,000 feet of elevation gain is the equivalent of traveling north 300 miles. Remember that the next time Alex Trebek asks you about it on Jeopardy. Or the next time you climb a mountain in Maine.
Perhaps you’ve been on a mountaintop, admiring the view, and thought to yourself, “Hey, the birds are different up here.” You’re correct. Elevation changes everything.
Generally, the temperature decreases three degrees for every 1,000 feet of elevation gain. Summits also get more than their share of moisture, and the earth dries out more slowly up there. Naturally, the vegetation adapts to the harsher environmental conditions. As habitat changes, so do the birds.
Pick a mountain, any mountain in Maine that’s at least 3,000 feet tall. Notice what happens. At the base of the mountain, the forest is typically hardwood. It’s likely to be a mix of maples and oaks, birches and beeches, maybe some pines and hemlocks. The trees are tall, and the forest floor is shaded. But within half an hour of walking up the trail, you begin to notice that yellow birch is taking over from white birch. Oaks are disappearing, replaced by balsam firs. These trees prefer a cooler climate.
Another half-hour later, the forest has changed again. The trees are shorter. There may still be some maples and birches, but they are stunted. Often, there are nice views from the mountain ledges overlooking the valley, as the dwarfish trees no longer obscure the full panorama. Red spruce is beginning to take over.
By the time you’ve climbed 90 minutes, spruce becomes the dominant tree species, and even these trees are getting shorter and thicker. Upon reaching the summit, or at least upon passing the 3,000-foot mark, the “trees” look more like shrubbery – stunted and impenetrably thick. On the taller peaks, it won’t take long before you’re above the tree line altogether.
Now: as you climbed, what thrushes did you hear? At the base of the mountain, you might have heard a wood thrush, which has a strong preference for mature hardwood forests. Hermit thrushes flourish in Maine’s mixed forests, and you don’t have to walk far up the trail before they completely take over. After an hour of climbing, you begin to hear the Swainson’s thrushes. They prefer a cooler coniferous forest. Their songs will follow you all the way up to 3,000 feet. Once there, in the short, twisted spruce, you might hear the song of a Bicknell’s thrush — an alpine bird that nests exclusively in this stunted zone.
You don’t even have to hike to get this effect. Drive up the west side of Baxter State Park. Initially, at the entrance gate, all you hear are hermit thrushes. But within four miles, usually after you’ve driven past Abol Campground, you’ve gained enough elevation that the Swainson’s thrushes become more numerous.
The same thing is happening with warblers. At the trailhead in the mature forest, canopy-loving birds are abundant. Northern parulas and black-throated green warblers are everywhere. The subtler song of the Blackburnian warbler descends from his hiding place in the foliage. Ovenbirds call from the understory. Soon, a short way up the trail where birches and beeches take over, the black-throated blue warbler might be heard more often. When you pass 2,000 feet, and stunted trees are no longer holding back the full sun, American redstarts and magnolia warblers pop up. Higher up, in the stunted spruce zone around 3,000 feet, blackpolls and bay-breasted warblers become common.
Flycatchers do it. Alder flycatchers may call from the trailhead parking lot, and eastern wood-pewees may echo through the mature forest, but by the time you reach the summit, all you hear are yellow-bellied flycatchers. Grouse do it. Ruffed grouse may drum near the bottom of the trail, but you’re more likely to trip over a spruce grouse near the summit. Chickadees do it. You’ll find black-capped chickadees at lower elevations, but boreal chickadees in the stunted spruce atop the peak.
Perhaps the strongest evidence that altitude simulates latitude is provided by the American pipit. It’s a bird of the northern tundra. You might have to drive to Labrador to find one in summer. Or you can just drive New Hampshire’s Mount Washington Auto Road. In all of New England, there are only two places pipits can be found breeding: near the summits of Mount Washington and Katahdin, where the local climate is definitely tundra-like.
So go climb a mountain, and report back to me. I’ll wait here.
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 email@example.com.