Change is normal in both nature and society

By BILL CHAISSON
Of a Feather
This morning, as I was about to get into my car and go to work, I was pulled up short by the din of several birds chasing each other around and uttering a stream of two-note calls. Eventually I determined that they were a brood of juvenile kestrels. They were about blue jay sized, had long pointed wings, banded reddish tails, tended to hover in one place, and when they perched I could see the characteristic falcon malar stripe below the eye.

I have always thought of kestrels as common and ubiquitous, but their numbers have been contracting over many years, especially in New England. So I was cheered to see this noisy brood racketing around my neighborhood, as I don’t see the species as often as I once did. This morning’s encounter made me recall a project that I did in college that involved tracking four species that were mysteriously expanding their ranges.

While I was in college I tried to bridge the arts and sciences by maintaining majors in English and biology. I read Jacob Bronowski’s “Ascent of Man” and C.P. Snow’s “Two Cultures” essay and was convinced that the estrangement between the humanities and science communities was something that had to be mended. My idealism faded as I moved into graduate school in the sciences — I didn’t have the courage to try making a living at creative writing — and I have instead ended by having successive careers, first in science and now in the humanities, instead of managing to bridge them.

As a consequence of this personal trajectory, I tend to reflexively see parallels — metaphorical and actual — between natural and cultural phenomena. One of the scientific topics that has fascinated me over the years is biogeography. Why do animals and plants live where they do, and how and why does this change over the years? The short answer is that the physical environment changes over time and the biota have to respond. This is one of the places where I see a parallel between nature and culture. Both change through time in response to outside (exogenous is the $64 word) forces.

It is thought that the kestrel contraction is due to the recovery of forest communities as agricultural land has been abandoned. If this is so, then it would be an anthropogenic (human originated) cause.

The four bird species that I studied in college were the blue-gray gnatcatcher, the red-bellied woodpecker, the tufted titmouse, and the Carolina wren. All of these were southern species that were steadily extending their range northward through New York State. My advisor sat me down with stacks of back issues of “The Kingbird,” the journal of the New York State Ornithological Association. This would have been in 1980, and I was looking back about 30 years for recorded sightings of each species. Indeed, all of them were showing a two-steps-forward, one-step-back pattern of advance.

The question was, “why”? Anthropogenic global warming was certainly not the pop culture phenomenon that it is now, but in my own experience the 1970s of my teens constituted a series of much warmer winters than the 1960s of my childhood. The biogeographic trend had , however, been going on since before this decadal shift, and I was told that it was most likely caused by ongoing recovery from the last ice age.

Although the Pleistocene/Holocene boundary was then put at 10,000 years before present (BP) — it is now placed at 11,650 BP — subarctic conditions persisted in New York and New England until about 7,000 BP and later climate episodes like the “Little Ice Age” of the 15th through 18th centuries likely forced some species southward or prevented them from expanding, well after the end of the last Ice Age.

Because I spent many days of my youth roaming through the woods of Merrimack County, New Hampshire and Dutchess County, New York I grew up being aware that the cultural settlement patterns — the metaphorical equivalent of species distribution — do not stay the same either. In rural Merrimack County (Danbury mostly) I encountered stonewalls, cellar holes, and graveyards amid mature hardwood forest far from any contemporary settlement. In distinctly less rural southern Dutchess County (Beacon and Fishkill) I explored empty factories, defunct railways, and abandoned summer cottages. Like nature, civilization expands and contracts in response to outside forces. Land uses, no longer sustainable, move elsewhere (i.e., change their distribution) or disappear entirely (i.e, go extinct).

We make the mistake of thinking the world around us is static, but the landscape is in a constant state of evolution, and the various aspects of it change at different rates. Forests in the Northeast U.S. recovered within decades of abandonment. The deserts of the Southwest, however, were created through overgrazing by Spanish cattle in the 17th and 18th centuries, and the native grassland has not yet returned. The factories of Beacon emptied out through the 1970s and will not return; the Nabisco box factory of my youth is now an art museum.

The first breeding record of the Carolina wren in New Hampshire was in 1991, 11 years after I painstakingly documented their northward spread through New York state. They are non-migratory, so they are “knocked back” by harsh, snowy winters. But apparently outside forces are insuring that we will have fewer hard winters and more Carolina wrens.