A Sweeter Trill in the Trees

Of A Feather
Bill Chaisson
Last June I heard an unfamiliar song in our overgrown pasture that turned out to be a field sparrow. He may have been looking for a place to start a second brood or perhaps he was an unattached male. A similar phenomenon may be unfolding this June. Twice in the past week I have heard a familiar trill at the edge of the woods at the northwest corner of the meadow. It sounds like a chipping sparrow, but richer and fuller, and is also at a lower register than a dark-eyed junco’s song. When I hear this bird I always recall a mitigated failure that I experienced in spring 1980, when I flubbed the “Griscom test.”

When I arrived at college in fall 1978, I was an accomplished birdwatcher because for the past eight years I had spent hours every week out and about with binoculars. At college I found other interests, both academic and not, and I did not do as much birdwatching as I had. However, I took an ornithology course in my sophomore year and was at the same time the teaching assistant for it. I also had a girlfriend who was singing the praises of summer restaurant work on the Maine coast.

My ornithology professor recommended me for a summer position as a naturalist working … I don’t remember who I would have worked for. The Audubon Society? The Department of Environmental Conservation? In any case, in late April I borrowed my girlfriend’s car and drove up to Massena for an interview of sorts. I met an older man at a woodlot near some giant transmission lines that led away from one of the dams on the St. Lawrence River. With very little preamble, he turned to the woodlot and asked me, “What kinds of birds would you find in there?”

This is the approach made famous by Ludlow Griscom. Birds are not randomly distributed on the landscape; they all have their own ecology and are much more likely to be in some places than others. During the drive up from Canton I had crossed some of the bleakest countryside east of the Mississippi. The North Country above the Adirondacks is flat, open, and empty. There is a kind of grandeur to it, but it is a lot less picturesque than the Maine coast.

The woodlot that I was staring at was a mix of conifers and deciduous trees with the latter predominating. While there were large trees, forming a continuous canopy in some places, there were also openings, filled with saplings and shrubs. There may even have been some scrubby areas filled with herbaceous vegetation. Certainly I was standing in that as I looked into the woods.

In other words, it was a very diverse floral community and would therefore support a diverse faunal assemblage. It was not an easy test. As I began to list species that I thought should be present, a bird began to sing at the edge of the opening in front of us. I didn’t know what it was and my interviewer’s body language instantly communicated disappointment. I knew that this was a sort of make-or-break moment, and I also knew that I did not want this job. Unlike today’s youth, in the late 1970s a 19-year-old was not likely to find satisfaction in pleasing an older authority figure who was testing them all the time.

I reasoned through the identification aloud in a desultory way. It was a melodious trill that reminded me of a junco, but the environment was wrong. I decided it was a rather adventurous chipping sparrow with a sweeter than usual song. My interviewer just grunted, told me it was a pine warbler, and brought our encounter to a quick conclusion. It was not a canny career move on my part, but I sure had fun during those two summers on the Maine coast.

The pine warbler (Setophaga pinus) really does prefer pines (unlike, say, the palm warbler, which is found among palms only incidentally during migration). I learned my warblers here in central New Hampshire, where there are abundant pines, but never saw this species. I didn’t see them on the Maine coast because they actually avoid spruce, fir, and larch forests. I spent the most time with them when I lived on Martha’s Vineyard amid the oak-pine assemblage that covers much of the island. A couple of pine warblers had territories (were singing that pretty trill) within earshot of where we were living on the south shore, but they were absent from the nearly pure scrub oak assemblage at the center, which was filled with prairie warblers and towhees.

S. pinus is unusual in that it lives primarily in North America throughout the year. The populations in the southeastern U.S. are permanent residents, and birds from the north-central and northeastern states and southern Canada rarely migrate as far as the Caribbean or Mexico in the winter.

In 1999 evolutionary ecologist Douglas Levey and others discovered that, unique among wood warblers, S. pinus undergoes a seasonal enzymatic change that allows them to digest seeds during the winter. They are the only warbler to have a predominantly seed diet, an adaptation that allows them to remain further north in the winter. Yellow-rumped warblers (S. coronata), which also winter in North America, eat some seeds during the winter, but focus on fruit.

Pine warblers are conservative-looking members of the Parulidae. They are green above and yellow below with indistinct darker streaking on the breast and sides and darker wings with two white wing bars. The female is browner above and paler yellow below.

I went on to get a Ph.D. in micropaleontology, not ornithology, and did all my field work at sea staring down a microscope, not in woodlots with binoculars. The pine warbler singing in my woods reminds me of a road not taken.