Current Nature: Overwintering Strategies

As the weather gets colder, animals must adapt to survive the winter. Some animals forgo dormancy completely. Birds migrate, deer grow a thick winter coat, and squirrels cache nuts to have a reliable food source. Other species undergo physical, chemical, and habitual changes to their bodies to counteract the cold and the reduced daylight. Many people are familiar with hibernation in mammals, but unique processes also exist in other species.

Reptiles such as turtles will brumate, which is analogous to hibernation but relies on a different process. Whereas, hibernation relies on stored fat reserves, brumation is based upon the animal lowering its metabolic activity to enter a state of long-term inactivity. They are usually lethargic but unlike true hibernation, they can move around if needed. Nantucket’s two freshwater turtle species, the Eastern Painted Turtle and the Spotted Turtle, tend to burrow into soft soil or hide under vegetation during brumation. 

Our Snapping Turtles overwinter in ponds. Sometimes, when the water freezes over, Snapping Turtles can be found moving about under the ice but otherwise, they tend to dig themselves into the mud. Snakes also brumate and seek out underground spots to spend the winter. However, unlike turtles, snakes will follow each other’s scent trails and use a shared hibernaculum. Sometimes hundreds or thousands of overwintering snakes can be found in the same location. On Nantucket, we have six species of snakes. The most common one that people encounter in the winter is the Eastern Garter Snake, as they sometimes try to use basements or crawlspaces as hibernacula. But keep an eye out for Milk Snakes, about a decade ago, the UMass Nantucket Field Station was renovating their septic system and they discovered a large group of Milk Snakes overwintering in the old cisterns being removed.

Insects also use specially adapted overwintering strategies, the most fascinating of them being diapause. This is when a juvenile insect suspends its development due to the adverse environmental conditions in winter and then later resumes that development in the spring when warmer weather returns. Many moths are known for this, but the most famous is the Isabella Tiger Moth, whose caterpillar is known as the woolly bear. Woolly bear caterpillars emerge in the fall but will not become moths until the next spring. Instead, they undergo a controlled freeze of their body. 

Their heart stops beating, their gut stops moving, and they produce a cryoprotectant that works like anti-freeze to prevent them from becoming completely frozen solid. In the spring the process is reversed and they re-emerge to metamorphize into moths. Juvenile solitary bees undergo a similar process while adults look for cozy wintering spots to burrow into. These may be in trees, sandy patches of bare ground, or in human-created bee houses. At the Linda Loring Nature Foundation property, we have a bee hotel, if you look closely at some of the tubes, you will notice that the openings are covered up, indicating that a bee has entered that hole and is overwintering there.

It may be cold and dreary outside, but at least as humans, we have home heating, fluffy clothes, and artificial light. This winter let us take a moment to marvel at nature and the unique strategies species have developed to survive and emerge again in the spring.

Stay tuned for more editions of Current Nature, a bi-weekly column featuring seasonal topics, natural history information, and advice on the outdoors from the staff at the Linda Loring Nature Foundation.