NORTHERN TIMBER RATTLESNAKES
By Niki Wilson
[1] In the rugged terrain of the Adirondack Mountains in New York State, biologist William Brown of Skidmore College has spent 36 years getting to know
a local population of timber rattlesnakes (Crotalus horridus). He has traveled through gnarly forests and up rubble-filled slopes to find these snakes near
the same dens [tocas] year after year, sometimes curled up in the leaf litter, other times basking [tomando sol] on stony outcroppings near shelter rocks.
[2] Timber rattlesnakes are members of the pit viper family, meaning they have temperature-sensitive openings or "pits" on the sides of their heads. Though
venomous, they are shy snakes, preferring to crawl away rather than strike. They hibernate in their dens during the colder months, mating in the late
summer. The breeding habits of this species have particularly captured Brown's attention, as understanding the rattlesnakes' reproductive behavior is key
in determining how to protect them.
[3] Last fall, armed with decades of data, Brown revealed some of his long-term findings. One of the biggest surprises was the average age of first
reproduction in females, something not previously confirmed, and an important piece of the lifecycle puzzle.
[4] Whereas females of other rattlesnake species, and even certain southern populations of timber rattlesnakes, begin reproducing around age three,
Brown showed that northern female timber rattlesnakes are roughly ten years old before they bear young for the first time. "They seem to have one of the
oldest ages of sexual maturity known in rattlesnakes," says Brown, adding that their age of first breeding varies significantly by population and geographic
location.
[5] Not only is it a long wait to mate, but many females – about 60% of those studied – will only have the energy to reproduce once in their lifetime. When
they do have sufficient reserves to carry a pregnancy, sometimes up to 20% of the litter (which normally totals between four and ten young) will be
undeveloped or dead at birth. Pregnancy and birth take an enormous toll on the mother, says Brown. “If she survives, several years may be needed for her
to build up the energy stores to do it again, if at all.
[6] Knowing how vulnerable the females are makes the protection of their core habitat critical. For example, Brown has found that timber rattlesnakes
require about a two-kilometer radius of undisturbed basking habitat around their dens while pregnant. The New York State Department of Environmental
Conservation is currently in the process of identifying such areas in an effort to develop a formal recovery plan.
[7] The snakes need it. Though currently stable, this population's future is far from secure. It is listed as "threatened" in New York State. In the past, numbers
dwindled due to poaching [caça ilegal] and the now-illegal collection for the pet trade. However, according to Brown, "The main threat most recently, at
least in New York State, is residential development up against timber rattlesnake range.”
[8] Brown has also discovered new information about the snake's lifespan. One memorable day last year, he re-captured a female snake he had first tagged
in 1981. She was roughly fifteen years old back then, meaning that last year, she was around age fifty. ''I'd always assumed they lived until they were
about twenty to thirty," he says. "Prior to this study, most herpetologists wouldn't have believed they could live this long.”
[9] It's another surprising and important piece of the lifecycle puzzle, one that can only come from a lifetime of work on a single population.
Adapted from Natural History, April 2017.
Before William Brown made his discoveries about northern timber rattlesnakes,
