Of seeds and serpents
October, 09, 2008
This appears to be a mast year for oak trees, a time when there is a dramatic increase in acorn production. More small rodents will survive the winter after a mast year when food is plentiful, and that in turn could mean a bonanza for their predators in the coming spring.
I was musing along these lines while hiking in the mountains recently when I came upon two timber rattlesnakes. Nothing sets the heart to racing quite like finding a fat-bodied pit viper, more than 4 feet long and thick as your forearm, lying beside the trail or coiled in your flower bed.
Most of us in this area have never seen one of these snakes (and perhaps are glad to have missed the experience). But it was once part of my job to figure out their conservation needs, and I never tire of seeing them.
The eastern timber rattlesnake, Crotalus horridus, is typically shy and non-aggressive. Whether they were always this way, or the more assertive individuals were culled from the gene pool by shovel and club, is an open question.
To the Puritan mind, the New World wilderness was the Devil’s country, and its serpents, like witches, were not suffered to live. The land “teemed with rattlesnakes” in numerous reports from Burgoyne’s terrified German mercenaries on their march toward Saratoga.
Timber rattlesnakes have a hard enough time maintaining a stable population without having to contend with poaching and human fear. They have poor reproductive success, a combination of high juvenile mortality and low population numbers. They breed on approximately three-year cycles, and gravid females do not eat at all in the seasons before giving birth. Their young are born alive in late summer and have a very small window of opportunity to catch a meal before hibernation.
One might assume that approximately a third of the female timber rattlesnakes of reproductive age would be gravid in any given year. However, researchers consistently observe that they find very little evidence of reproduction in some years, followed by a “pile up” year when most of the female snakes in a population give birth. This corresponds rather well to the availability of prey following a mast year for oaks.
Things were different, though, back when the land was covered with American chestnut, that keystone species of the New England woodlands whose loss we still cannot calculate. Chestnuts, you see, had no mast years.
They produced regular amounts of seed, providing an important food source for the small rodent population but one which, by itself, would not cause large variation in their ability to over winter from year to year.
Perhaps when the chestnuts were still a major part of the forest ecology, timber rattlesnakes reproduced in about the same percentages each year. I am aware of one researcher whose observations appear to support this hypothesis, but so much remains to be known about these snakes that for now I can merely speculate.
It was too late in the season for the two rattlesnakes I observed to be breeding. They were waiting out the last pale days of September before drawing back into the granite darkness until another spring stirs their dormant coils. Beneath the forest litter, chestnut roots still push their shoots bravely toward the sun.
Tim Abbott is program director of Housatonic Valley Association’s Litchfield Hills Greenprint. His blog is at greensleeves.typepad.com. He and Fred Baumgarten will write Nature’s Notebook on alternating weeks.
© Copyright 2008 by TCExtra.com
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