Western Tanager Credit: Bob Duchesne

I’ve been travelling a little bit lately. How’s your summer going? My trek took me through South Dakota, Montana, Alberta and Saskatchewan, then back home via all the remaining Canadian provinces between there and here.

Traveling is a good chance to get reacquainted with humility. I have a superpower. I know almost every sound a Maine bird can make. However, put me in the Rockies among unfamiliar birds and my powers weaken. It’s kryptonite.

But wait. Many Maine birds are also Montana birds. The most abundant bird by far was the Swainson’s thrush, which is also a denizen of Maine’s spruce forest. Ruby-crowned and golden-crowned kinglets were common. We share many woodpeckers, plus northern forest birds such as gray jays and spruce grouse. Much to my surprise, warbling vireo was the most common vireo; it haunted every campsite. Warbling vireos breed in pockets throughout Maine. In Bangor, Essex Woods Marsh is the best place to encounter them, but in the Rockies, they seemed to be everywhere.

What we don’t seem to share is warblers. Maine is renowned for having lots of warblers. In Montana, I encountered maybe six species total. At home, I can hear that many from the front porch before breakfast. In a good day of birding in the Pine Tree State, I’d expect to meet 16 to 20 warbler species.

This disparity caused me to think about how nature works. Across the northern portion of this continent, the spruce-fir forest is relatively unbroken. Birds are free to expand their ranges from east to west. But through the central part of the United States, there are significant barriers to east-west expansion, particularly the Great Plains and the Continental Divide. Perhaps there was a time during the last Ice Age, when there was unbroken habitat along the glacial edge. Once the ice receded, barriers emerged, populations became isolated and these evolved into different species.

But not that different. Some of these related groups now look different, but they can sound very similar. The western counterpart for Maine’s rose-breasted grosbeak is the black-headed grosbeak. Not only are their songs nearly the same, but the “chink” call note is also practically identical. There are scarlet tanagers in the northeast, summer tanagers throughout the south and western tanagers throughout the Rockies. The three species look different, but they sing remarkably the same.

The mourning warbler is a secretive songbird that is found in regenerating clearcuts in northern Maine. In the Rockies, MacGillivray’s warbler occupies the same habitat niche, quickly colonizing the brambles where forest fires have opened up the canopy. The two look, sound and act so much alike that I laughed out loud at finding my first MacGillivray’s warbler in Glacier National Park. It skulked around like a Maine mourning warbler, and even showed its annoyance by uttering the exact same “spit” call note.

Montana’s red-naped sapsucker acts exactly like Maine’s yellow-bellied sapsucker. They even share a preference for territorial drumming on metal.

So, between the species common to Maine and Montana, and the species that sound similar, I slowly regained my superpower and could recognize about 80 percent of what I was hearing, despite being so far from home. Which is the point of today’s column. Much of what you know about birds in Maine is transferable.

Up to a point. There are also birds that are visually indistinguishable from each other, but sound very different. Evolution is a funny thing. The western meadowlark looks virtually identical to an eastern meadowlark, but their songs are radically different. Eastern and western wood-pewees are twins, but there is little similarity in their vocalizations. Recently, scientists decided that Maine’s winter wren is actually two different species, and renamed the western version as the Pacific wren. I can’t tell them apart visually, but the song of the Pacific wren is definitely faster, with more notes per verse.

In Maine, I need only learn the vocal difference between black-capped chickadee and boreal chickadee. In Glacier, both are present, but so are chestnut-backed chickadees, which call a little like their black-capped cousins, and mountain chickadees, which sound more like boreal chickadees, and sing a bit like a white-throated sparrow.

Naturally, there are some birds in the west that throw me completely off my game. The varied thrush looks and acts somewhat like an American robin. But in the evening, it utters a plaintive note from the treetops that sounds like a child’s police whistle being blown through a kazoo. I’d never heard anything like it.

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