Now that the days are becoming shorter and nighttime temperatures are beginning to drop, Wellfleet Bay’s resident box turtles are preparing for brumation, the reptile version of hibernation. Unlike a woodchuck or a bear, turtles do not fatten up and snooze the winter away in a cozy den. In fact, it’s almost the opposite!
Last May, we began our first long-term study of juvenile box turtles, focusing on five turtles that were “head started” over the last winter at Bristol Agricultural High School in Dighton. The youngsters were released on the sanctuary outfitted with radio transmitters to allow periodic monitoring.
These two-year-old turtles are the size of five to six-year-old wild box turtles. Our primary study goal is to determine if they will behave like the youngsters that they are, or like the somewhat older turtles they resemble. Although our study is still in its early stages and is far from conclusive, I would characterize the behavior of our head starts so far as more typical of two- year-old turtles than six-year-olds.
Each head start was released in a different area of the sanctuary. They spent most of their time hiding under leaf litter or buried in detritus, which is very typical for small (two-year-old) turtles. Certainly our hot and very dry summer may have contributed to this behavior, but in general their movements were few and when they did move they didn’t venture very far. This helps to explain why seeing a tiny box turtle in the wild is such a rare occurrence; they hide most of the time and just don’t move much.
Because of the heat and drought, this was not a good growing year for box turtles. Many of them estivated—or were dormant– all summer. Regardless, each of the hatchlings appeared healthy when I weighed and measured them recently. Two were up a few grams in weight and two were down a few grams. One turtle has had a transmitter failure, so its exact location is unknown. The transmitter problem could be caused by a malfunction of the electronics or by a small critter like a chipmunk gnawing the antenna off (yes, it happens). I know in general where the turtle is and I’ll spend some time searching for it now that the vegetation is receding.
Box turtles on the sanctuary property begin to enter brumation toward the end of October and the last one disappears around Thanksgiving. Their body temperatures cool gradually, and –unlike mammals preparing for hibernation–they’ll stop eating weeks before brumation in order to empty their GI tracts. Trying to brumate on a full stomach could be fatal, as food still in the GI tract could decay and lead to an infection.
Each turtle selects a brumation site in well-drained yet moist soil or leaf litter and digs a burrow where they slip into a state of torpor until April or May. Somehow, they know just how deep to dig their burrows in order to avoid freezing temperatures. The burrows here in Wellfleet range in depth from about one to seven inches, with the average being a mere two to three inches. How do they survive the cold? Box turtles are freeze tolerant; they are the largest vertebrate that can withstand icing of their internal organs (for a short period of time).
One of the behaviors that we will be watching for this fall will be when the head starts begin digging their first brumation burrows and settling in for the winter. Let’s remember that these turtles spent their first two winters in captivity, warm and with plenty of food. Will they know when it’s time to brumate? Will they know how and where to dig? I suspect they will, but like a guardian angel I’ll be watching!