It’s the middle of August, and the heat and humidity have chased me to the relative coolness of Centennial Woods, a 147-acre patch of forest owned by the University of Vermont. There’s not much stirring in the midday heat. Until, that is, I hear the tapering whistle of an eastern wood peewee ringing out from the canopy above. The sound is striking against the noticeable absence of other birds singing this late in the season.
Naturalist Aretas Saunders calls these post-nesting songs – unique to songbirds – “revival songs”, and Alida Chanler’s 1917 story in Country Life in America describes the revival song of the peewee as though the peewee, like her audience, belonged to the leisure class: “With languorous nonchalance he [sings] ‘Pee-a-wee, pee-yer.’ There is nothing matter of fact about the peewee. His is the luxurious ease of the contented loafer. His soothing drawl lulls to meditation; all tension relaxes, and Nature’s mood of brooding content fills the woods.”
I locate the peewee I’ve been hearing in a mixed stand of hardwoods and softwoods. He’s taken a break from singing, and I watch him swoop out over a brook and catch a fiery-red dragonfly on the wing in a frenzied display of acrobatics before returning to his perch. I hear the faint slapping of the insect’s wings beating frantically against the peewee’s perch before he devours the meal.
As a mid-sized flycatcher, peewees have found a narrow niche between the larger great crested flycatcher, which hunts in the upper canopy, and the smaller Acadian and least flycatchers of the understory. Not only do peewees feed only in the mid-canopy (the layer of vegetation roughly between 20 and 50 feet above the ground) but they also nest here. One hundred and fifty years ago, when this forest – and much of New England – was open pasture, the grazing cows might have heard the late-season twitterings of goldfinches staking claim to the few scattered shade trees. But without a mid-canopy, they would not have heard pewees.
Today, this forest’s thick mid-canopy supports a healthy peewee population. But data from the North American Breeding Bird Survey indicate that this bird is on the decline in New Hampshire and Vermont. And one of those reasons is an unlikely suspect.
On a nearby sandy slope, young, shade-tolerant hemlocks are thriving in the understory. The well-worn trails leading in and out of the hemlocks are a sure sign that this stand is busy with deer in late fall and winter. Since deer are limited primarily by their ability to find adequate winter shelter, where there are hemlocks there will be deer.
Prior to European settlement, hemlocks comprised about ten percent of Vermont forests; nearly three centuries of cutting and regrowth have reduced that to less than five. A quarter of a mile downstream from me and just upstream from the Winooski River is the former site of TJ Rutters Wool Pullery Co., which processed hides from locally-killed livestock from the early 1800s to the 1860s. In the mid-19th century, ten miles was the farthest a tannery like Rutters could afford to source hemlock. As the local hemlocks disappeared in an ever-widening circle, so did the deer.
Habitat loss, combined with over hunting, dropped deer populations so low that, in 1865, Vermont put a moratorium on deer hunting to protect the struggling herd. The population didn’t start recovering until 1878 when 17 deer from New York were released in Vermont.
At the same time, the trains that brought those deer in were opening up access to the Midwest, and tanning operations became concentrated in industrial areas like Chicago and Boston, closer to the meat packers and shoe manufacturers. With fewer farms and outsourced tanneries, the hemlock slowly returned and the deer populations began recovering.
The deer herd in Vermont averages between 5 and 25 deer per square mile. According to a 10-year long Forest Service study in Pennsylvania, a density of 20 deer per square mile is enough to negatively impact mid-canopy nesting birds like the peewee. At this density, deer browsing patterns alter forest structure by eliminating the understory. Given enough deer in an area eating the buds of saplings (adult deer eat 3-5 pounds per day of woody material in the winter), most trees don’t grow past the sapling size, which prevents the mid-canopy from regenerating itself.
The historically low density of deer in the early twentieth century has afforded us today a robust mid-canopy with healthy breeding populations of peewees all across New England. But with fewer people hunting and more deer wintering grounds than a century ago, sustained high densities of deer will reduce the regeneration of peewee habitat and make those lazy August afternoons a bit quieter in the future.