Summer World_ A Season of Bounty - Bernd Heinrich [101]
I’ve just noticed that the raven pair living within earshot of our house have noisily returned to their nest site on the cliff, as though getting ready to renest. Invariably (so far) they will break off their apparent interest in a month or two (although there are reports of European ravens occasionally nesting in the fall). A friend reported seeing an osprey carrying a stick as though preparing to nest, and someone e-mailed to tell me he saw a raven pair near Bethel, Alaska, bringing sticks to their nest in mid-October. At this time of year the ruffed grouse occasionally drum in the woods, as they do in the spring when attracting mates. It has been claimed that this Indian summer activity is for “setting up territories,” but instead most of the grouse are now almost semi-social, often feeding and resting together in small groups.
Woodpeckers also occasionally drum, and bluebirds have come and examined nest boxes. Other birds sing again, after a silence of at least two months. Daily I hear swamp, song, and white-throated sparrows; starlings; ruby-crowned kinglets; blue-headed vireos; and occasionally American robins, phoebes, and ovenbirds sound out abbreviated and somewhat hesitant renditions of their distinctive refrains, in what seems like a muted, halfhearted way. They usually give only the first few notes of their song at half volume and then it trails off as though they have changed their mind. (The spring migrants coming through do the same.)
Birdsong is a male prerogative that functions to lay claim to a territory and keep other males out, and possibly also to attract a mate. But many of these singing birds that I hear now are migrating south, moving through to their wintering grounds. None of them will form pair bonds or seek breeding territories until next spring and summer. In short, their singing is out of context and off schedule by about six months.
Perhaps singing is now a response of heightened exuberance that is normally reserved for the spring. But if so, it’s a proximal, not an ultimate, response; exuberance can’t explain plants’ behavior. By late September I occasionally find not only the previously mentioned plants in flower in Vermont, but also at least one other species, the bunchberry, Cornus canadensis, in the Maine woods, near my camp. Bunchberry has flashy white flowers that carpet the north woods for two weeks in May. They are absent through the summer. When these flowers now reappear next to the plant’s bright red berries and among fallen red, brown, and yellow tree leaves, they make a curious anomalous contrast.
None of the late flowers of the bunchberry will develop fruit. Many of them are misshapen as well, reminding me of the “imperfect,” muted birdsong at this time. I suspect that unseasonably warm fall temperatures (global warming?) would cause even more flowers to bloom in the fall, but temperature per se does not make them bloom, because it is invariably hotter in the previous months of summer, yet no flowering response is induced then.
Fig. 40. Many of the off-season bunchberry flowers are misshapen.
Does the end of summer contain the seeds of spring? There are vast differences between summer and winter in temperatures and hours of light versus day, but there is much that is similar between the beginning and end of summer. Both tend to be cool times of year. And at the fall and spring equinoxes—22 September and 20 March, respectively—the photoperiod is identical: twelve to twelve (twelve hours of day and twelve of night).
Some flowers bloom in the spring, others in midsummer, and still others in the fall. In the laboratory one can induce one plant to flower under the