One of the more gratifying aspects of birding is the way even familiar species find ways to surprise you. Common birds turn up in new settings at new times, or do things you’ve never seen them do before. Despite a good half-century of experience with the birds of Eastern Massachusetts, I can’t spend a single day in the field without seeing something new.
A good example came up about a week ago, involving a hermit thrush I encountered at the Nature Conservancy’s Hoft Farm Preserve in West Tisbury. While never exactly a common bird on Martha’s Vineyard, the hermit thrush is a regularly occurring one, especially during fall migration and into the early winter. I probably run into two dozen or so in the course of a year, sometimes just getting a glimpse or even just hearing a call note, but sometimes getting a chance to watch one of these birds at length.
Like any species, the hermit thrush is capable of a certain amount of flexibility in its behavior; to survive, any animal needs to have some capacity for creativity programmed into its repertoire. But I’d consider the hermit thrush to be, in general, a bird of strong preferences and predictable behavior. As migrants or wintering birds, they like shrubby thickets, preferably damp ones. And they feed mainly on berries found in those same thickets, or on small invertebrates gleaned mainly on the ground, uncovered by the bird as its digs and scrapes in the leaf litter. You rarely see one foraging far from the confines of a thicket or a woodland.
This particular bird at the Hoft Farm, though, broke that pattern from the start. When I first spotted it, it was hopping along in short grass, a good 50 feet from the edge of the woods. The sun was out, the weather was mild, and the hunting was good: Every few hops, the bird zeroed in on some unfortunate bug or spider, deftly grabbing and swallowing it.
While the open setting was a bit odd, the basic strategy wasn’t that unusual, so I wasn’t too surprised. I enjoyed the chance to watch one of these secretive birds in bright light and away from cover. But then it pulled an elegant stunt, one I’d never before observed.
The decommissioned native plant nursery at Hoft Farm still has a number of fence posts standing, and it also incorporates a few modest saplings of oak or pitch pine. The hermit thrush flew deliberately to the top of one of the fence posts, scanned the ground in a full circle around its perch, and after a few seconds sighted some prey item in the grass, and dropped onto it like a stooping hawk.
It repeated the process a couple more times, then flew to the top of a small oak sapling, where it did the same thing. I followed the bird for about 10 minutes as it worked its way around the nursery area, moving from exposed perch to exposed perch, scanning for and then pouncing on prey. I’ve never seen a hermit thrush hunt like this, and can’t recall seeing a member of this species spend even a fraction of that much time out in the open.
Perch-hunting like this, however, is a standard hunting method — perhaps the most characteristic means of foraging — of the Eastern bluebird. Indeed, before noticing the hermit thrush, I had been watching a bluebird engaged in precisely the same behavior, even using some of the same perches the hermit thrush visited.
There’s no way to tell what was really going on. What I observed is certainly consistent with the idea that the thrush learned a foraging tactic by imitating the local bluebirds. Perhaps it invented the move on its own. Perhaps perch-hunting in a wide-open field is a normal part of the hermit thrush repertoire, and I just haven’t happened to witness or read about it in the past. But whatever the full story was, I had the pleasure of watching something I’d never seen across 50 years of birding, and hundreds of hermit thrushes.
I guess I shouldn’t have been surprised to witness this seemingly innovative behavior. I know that hermit thrushes are quite flexible in their diets: I’ve seen one catch and eat a salamander, and published accounts of this bird’s behavior suggest that a hermit thrush taking such comparatively big game is not rare. Once or twice I’ve seen a hermit thrush hawk an insect out of the air, sallying outward off a perch to snap up its prey like a flycatcher.
But the experience was one of those times when I’ve had to question how much I really know about the birds I watch. Do hermit thrushes do this often? Are they capable of learning new behaviors by observing other species? What other surprises are they capable of? The more I learn, the less I know.