Where Do Timber Rattlesnakes Spend the Winter? Communal Dens

What a timber rattlesnake den looks like

A winter den, which biologists call a hibernaculum, is a place where snakes can get deep enough underground to avoid freezing. For timber rattlesnakes in the Northeast, the Appalachians and the Midwest, that usually means a fissure in a rocky ledge, a jumble of fallen boulders at the base of a cliff, or a talus slope of broken rock. Gaps between the rocks lead down to chambers below the frost line.

Most dens face roughly south, from southwest to southeast. These slopes catch the low spring and fall sun, which lets snakes bask right at the den entrance before going in for the winter and after coming out in spring. Nearby open, rocky areas are used for basking, shedding and, for pregnant females, giving birth.

In the southeastern lowlands, where rock outcrops are scarce and winters are mild, timber rattlesnakes, there often called canebrake rattlesnakes, usually overwinter alone or in small numbers. They use places such as stump holes, hollow logs, tangles of roots and old animal burrows.

How long do timber rattlesnakes stay in their dens?

Snakes do not truly hibernate as mammals do. Their winter dormancy is called brumation: the snake’s body cools to the temperature of its surroundings, digestion stops and the animal barely moves, but it can wake and move when conditions warm. You can read more about this in Do snakes hibernate?.

In the northern part of the range, timber rattlesnakes may spend up to seven months a year at their dens. In New York, the active season runs from late April to mid-October, and in the far north of the state, emergence is often delayed until mid-May. Farther south the dormant period is shorter, and snakes in some areas have been found leaving their dens briefly in midwinter to bask on warm days.

Who shares the den?

Rattlesnake dens are often shared. Many northern dens hold roughly 15 to 60 timber rattlesnakes, and the same crevices are frequently used by copperheads and rat snakes. The reason is simple: good dens are scarce. A rock crevice deep enough to stay above freezing, in the right position to catch the sun, may be the only suitable site for kilometers around.

Sharing a den may bring other benefits as well. Genetic studies suggest that rattlesnakes using the same den, particularly pregnant females and young snakes, are often more closely related to each other than to snakes from neighboring dens. Young snakes seem able to recognize chemical cues from relatives, and this may help them find their way to the right den in their first fall.

Loyal to one den for life

Timber rattlesnakes show strong den fidelity, meaning that most return to the same den every fall, often for their entire lives. Since adults can live 15 to 20 years or more, and their young return to the same place, a good den can be used by many generations of snakes.

Young snakes learn the way. Newborns are born in late summer near the den, often at the rocky basking areas where pregnant females spend the summer. In fall they appear to follow the scent trails left by adults back to the den entrance.

Spring emergence and summer travels

When the rocks warm in spring, timber rattlesnakes emerge slowly. For days or weeks they stay close to the den, basking in the sun and sheltering under nearby rocks. Then most of them disperse into the surrounding forest to hunt and, for males, to search for mates.

In early fall the snakes head back, often along much the same routes, and gather once more around the den entrance before slipping underground for the winter.

Why dens make timber rattlesnakes vulnerable

Gathering in one place each year has a serious downside. Dens are where timber rattlesnakes are easiest to find, and for centuries people found and killed them there. In northern New York, some counties once paid bounties for rattles, a practice outlawed in 1971, and the state’s timber rattlesnakes have disappeared from about a quarter of their historically known dens.

Today the main threats around dens are illegal collecting for the pet trade, disturbance by hikers, climbers and off-trail visitors, development, and roads that cut across migration routes. Because the snakes are so loyal to their dens, losing a den or most of its adults can wipe out a local population that may never return. This is a large part of why the species is protected in many states, as explained in Are timber rattlesnakes endangered?.

If you hike in timber rattlesnake country, be extra careful around rocky ledges in spring and fall, never reach into rock crevices, and keep at least 2 m (6 ft) from any snake you see. Rattlesnakes rarely bite unless stepped on or handled, but if someone is bitten, call 911 or seek emergency medical help immediately.