Summer World: A Season of Bounty - Bernd Heinrich (2009)
Chapter 23. The Last Peep
25 September 2005. IT IS A CRYSTAL-CLEAR DAY AND bees are bringing in pollen from the goldenrod, which is now fading fast. The purple and blue New England asters are still going strong, but the American ash are starting to shed their now purplish leaves. The sedges in the bog are brown and a few sugar maples are turning yellow. The first frost is forecast for tonight, so technically we’re now beginning Indian summer. But we passed the fall equinox two days ago, when the sun spent twelve hours above and twelve hours below the horizon at every latitude on Earth. Here it is defined as the first day of fall (and it is the first day of spring in the southern hemisphere). From now on our days here will be gradually getting shorter than the nights, and that changing photoperiod will affect the physiology of trees, birds, and many mammals, to turn off growth and reproduction. It is therefore curious indeed that some spring-blooming plants are again showing signs of life—even our pear tree has a few blossoms. Dandelions are once again raising yellow flower heads. The phoebe sang briefly this morning after two months of silence, and spring peepers sometimes sound off with isolated calls at night.
19 October 2005. Windy, cool weather makes me feel restless and I’m looking forward to going to Maine tomorrow. The leaves are now falling thickly. Despite the cold and overcast weather a few more “spring” flowers have started to bloom—common blue violets (Viola sororia), self-heal (Prunella vulgaris), cranesbill (Geranium maculatum). I had been startled to see the spring-blooming pear and a crab apple tree that I transplanted in May again put out a few blossoms in late September. Now a wild honeysuckle in our driveway burst several of its hundreds of buds to grow twigs with leaves and flowers. A cottony white fluff ball drifts by on feeble wing beats—it’s the migrating form of the woolly alder aphid. I don’t know where it’s going, but it is of the summer’s last generation from wingless parents. I heard geese calling in the night. This morning about fifty of them sit quiet, like decoys, on the beaver pond. Suddenly, at about eight AM, they splash off toward the east; then they circle toward the north; and then the assembled flock heads west. A dozen remain on the pond. Only a few white-crowned sparrows—migrants passing through—are left here. A grouse drummed. I had not heard one since spring.
The beavers in our bog are again felling poplar trees, gnawing off the branches, and dragging them into the water to store them in their food cache next to their lodge, where the ice will soon cover them. Chipmunks gather acorns and with their cheek pouches stuffed full they scurry to and from their dens to top off larders in their previously prepared underground storerooms. I stock the woodpile, harvest the honey, and insulate the house and hives, while Rachel obsessively cans vegetables and makes apple pies. Meanwhile, overhead the geese honk on their way south, and in the nearby woods the rutting of moose and deer is timed so that the young will be born early enough in the spring to grow up and withstand the next winter. As always when summer ends, most of what I see (and try to do) makes sense. It should. After all, few animals or plants would survive a full year without changing their behavior as well as their physiology to prepare for the awesome, inevitable winter challenge. Given the strict and predictable schedules of the seasons, I am puzzled by any plants or animals that would be fooled enough to be far off schedule. Are they aberrations? But if so, why are there so many of them?
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 influence of artificial short days, whereas another will flower only if subjected to long days. Similarly, a constant laboratory photoperiod induces birds to either lay eggs or shut off egg production. Wild birds breeding in the north start their reproductive cycles, including all their behavior of migration, courting, and nest building, in an orderly progression influenced by photoperiod. Our chickens lay throughout the summer when the natural photoperiod is on average at least thirteen hours of light and eleven of darkness. But to keep the hens laying in the middle of the winter all we have to do is keep a light on in their shed for several extra hours. At the spring equinox, near the end of March, the photoperiod is rapidly approaching thirteen to eleven, and that is also the time when many organisms are preparing for summer. Since they use the photoperiod to inform them of what season they are in, how does the same photoperiod, at around the fall equinox in late September and the spring equinox in late March, allow them to differentiate spring from fall?
Temperature is too variable to serve as a reliable cue to differentiate the beginning from the end of summer. Plants and animals not only need to know when summer is or is coming, but also need to predict when it will begin and end. Any given photoperiod as such is not the only answer. It seems remarkable enough that any organisms can measure photoperiod and almost universally respond appropriately to it, but they need an added mechanism to determine the direction of the changing photoperiod. That seems a lot to ask for. When plants flower at an inappropriate time, this effect is often attributed to “stress” or to unusually high temperatures. Stress could indeed be a contributing factor, but perhaps the springtime photoperiod in the fall is in itself a stressor.
Fig. 41. One bud (of eight on this section of twig) of a honeysuckle bush that has opened to extend a twig with leaves and flowers in October; normally the plant blooms in late May.
Mistakes or imperfections provide variety for natural selection to work on, to permit evolution. There is even a mechanism whose only “purpose” is to produce variation. It’s called sex. If there were no variation, there could be no evolution. If species had been magically created, they would all be clones. It was a heritable mutation that caused central European blackcap warblers to misorient, so that they ended up flying west in the fall rather than south to Africa. These birds got a new population started, and they are now thriving in Great Britain. Some possibly misguided phoebes who abandoned cliffs and started nesting on houses became the norm because houses were safer. Salmon that did not find their home streams on their spawning migration and by chance ended up in other streams eventually colonized the new streams, expanding the populations. Possibly confused woodpeckers that wasted a lot of time and energy hammering pseudo nest holes in the fall found them to be useful places for overnighting during very cold weather, and they had a slightly better chance of surviving than those who seemed to be less misguided. Similarly, the rare blue violet that blooms in the fall reminds me that nature is not always proximally perfect, though it evolves and ultimately persists because of its imperfections.
FOR YEARS ON WARM NIGHTS AND SOMETIMES ALSO ON warm days in late summer and fall, I have heard strange, generally isolated high-pitched cheeps and chirps coming from our woods. Whenever I have stalked near to determine the sources of these birdlike calls, they have invariably stopped and I have seen nothing. It has taken me a while to finally establish that I was hearing the voices of apparently misguided spring peepers and wood frogs. In the spring these frogs collectively make a deafening din in their breeding ponds, and afterward they hop back onto land in the nearby woods, where they remain silent all summer. However, by September and early October, in Indian summer, when you again begin to hear their voices, they are never in breeding ponds but always in the woods, where they will overwinter under the fallen leaves. No bullfrog, leopard frog, or green frog makes the same “mistake” of calling as though jumping the gun to begin the breeding ritual six months ahead of schedule. But wood frogs do call, although not as frequently as the peepers and although the calls are usually very brief and isolated. Once while I was up in a spruce tree in Maine during November I suddenly heard a wood frog below me; then another joined it; then a third. They were separated by about 100 feet. There was no pool in sight. The three called for about ten minutes, and then resumed their silence. These were probably their last peeps of the season.
These fall-calling frogs are already filled with egg masses like those they will deposit half a year later, as I found out by accident. I had built an aviary enclosing a section of woods, and one morning at dawn in September one of the ravens inside captured and killed a frog. I immediately confiscated it to make a positive identification: it was a plump female wood frog carrying a full cluster of eggs that looked identical to what females freshly out of hibernation deposit in their breeding pools in April. If the frog had frozen the next day and thawed out in April, it would have awakened to another day of very similar temperature and photoperiod, and it might not know the difference, or might not know that anything had changed. The seven-month interval until these eggs would have been laid would have been, to a cold or frozen frog under leaves and snow and ice, a time of death when a minute is an eternity and an eternity a minute. The end of summer is also the beginning.