Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [100]
20
BERRIES PRESERVED
Wondering what the crows roosting in town eat in the winter, I collected bagfuls of their regurgitated pellets under the roost and picked the pellets apart. These undigested remains of what they had eaten that didn’t pass through their digestive tract contained mostly berry seeds. Some pellets consisted primarily of wild grape seeds. Others were masses of seeds from the common Viburnum species, and some contained wild holly seeds. In early spring many were almost pure bundles of undigested staghorn sumac seeds. Almost every kind of winter berry was represented in these crow pellets that can be as much fun to pick apart as owl pellets full of bones and fur.
Only nine of the thirty-eight local species of berries that I know of ripen and rot quickly. These are the summer berries, such as strawberries, June or serviceberries (Amelanchier), raspberries, black berries, blueberries, and chokecherries. They ripen in a progression from May through August and they spoil within several days. That leaves twenty-nine winter berries, which all ripen in the early to late fall. They are not sweet, but they last on the branch through the winter.
I have come to notice these winter berries as a consequence of watching birds. Berries and birds are intertwined in an ancient and complex mutual relationship that is as intricate and interesting as that of flowers and bees, although it is not always as visible or obvious because it proceeds over time spans measured by seasons rather than minutes.
Watching the different kinds of berries that are specific to winter can be a slow sort of sport, unless one has a good view and keeps a long-running score. I am lucky to have a beaver bog nearby which I routinely check to see what’s happening. Many berry species can be found there. The beaver pond is surrounded by a virtual hedge of arrowwood (Viburnum dentatum), a species whose dark-blue berries show up conspicuously because they are attached to the twigs by bright yellow stems.
Arrowwood berries provide a considerable bird feast in the fall. During the autumn of 2000, I counted and weighed the berries from twenty arrowwood bushes, estimated the number of bushes surrounding the pond, and calculated that the little beaver bog yielded slightly over a ton of bird food. From early September and into November, wave after wave of hundreds of robins came through, feeding for several days before moving on. Bluebirds, blue jays, starlings, grouse, and pileated woodpeckers also fed on these arrowwood berries, and I found not one berry remaining by early March, when the resident winter birds would presumably need them most. Indeed, by February arrowwood berries are dry, their yellow attachments to the twigs are brittle and faded, and the remaining berries then drop off. Thus, although fed on by many birds, these berries are apparently adapted for fall migrants.
Surrounding the beaver bog, though in much less abundance, are also maple-leaved arrowwood (Viburnum acerifolium) and nannyberry (Viburnum lentago). Both species have blue to black raisinlike berries, but unlike the V. dentatum, these stay attached by stalks that do not turn brittle. Furthermore, these berries are not consumed by the fall migrants. They can stay on the bushes all winter and they are fodder for resident winter birds such as grouse, purple finches, blue jays, and crows. If not fully removed, they then also feed spring migrants.
Winterberry, the common name for a holly (Ilex verticillata), should presumably also feed winter birds. It grows in swamps and wet places, bearing crimson berries. A bush laden with these berries, after the leaves are dropped in the fall, shines like a red torch that signals birds to come eat and ultimately to disperse the seeds. Yet, I had routinely seen resident winter birds, such as woodpeckers, chickadees, kinglets, blue jays, and grouse, in and