Animal activity as winter turns to spring

By Jeff Osborne - About two weeks ago, a nice marmot, Punxsutawney Phil, purportedly did not see his shadow after he was pulled from a prop tree stump and held aloft by a very formally dressed man. This is supposed to mean an early spring and warmer weather in February and March. Unfortunately, according to historic temperature data, this predictive method has been incorrect over 60% of the time. Maybe Phil is wrong on purpose because he wants to be left resting in his burrow a while longer like all his other woodchuck friends. There are many animals that slow their metabolic functions when food is scarce, like during winter in Pennsylvania, and some have a flurry of activity after the cold weather breaks in late winter and early spring.

              Last week as I drove to work, I smelled thiols which are chemical compounds that have a sulfur smell. They are found in skunks and added to natural gas. I smelled sulfur many times and then started to notice expired striped skunks along the road. On my way back from work, 45 miles, I counted nine dead skunks, which is a great increase from average. This great increase marks the beginning of skunk mating season and increased activity on their part. Most male skunks huddle alone during cold winter weather in underground dens. There they can enter a state of torpor. In torpor, they reduce their heart rate, respiration rate, and body temperature. This helps conserve energy and water. They can go into torpor daily for 9 to22 hours during winter. After the midpoint of winter, they leave their dens to find mates, often spurred by a period of warmer weather. Some skunks den in groups, with several females and up to one male. These skunks may not undergo torpor as they use less energy to maintain their body temperature and are able to expend their fat reserves at a much slower rate.

              Bats are another mammal in Pennsylvania that spend much of the winter resting. They enter a longer state of torpor, often called hibernation. Six of the nine species of bats common within the state hibernate here. For up to six weeks at a time, little brown bats can reduce their heartbeat below 20 bpm, versus over 1000 bpm during flight. They also reduce their respiration rate to about 10 breaths per minute, and their body temperatures dip to the ambient temperature of their hibernation spot, often around 40 degrees F. Big brown bats can inhabit your attic all year long, hibernating there in winter. Bats will break hibernation to replenish fluids and if disturbed. There is a great expenditure of energy to break hibernation, and if bats are disturbed too many times, they may not have enough energy to last until spring. In early spring, bats will burst forth to seek their roosting sites and begin the offspring gestation process.

              Chipmunks and woodchucks are some of the many rodents that slow their metabolic functions in winter. Many chipmunks undergo torpor for a few days at a time from late December through February, awakening to eat from their food hoard. Woodchucks store up fat to survive longer spells of torpor. Woodchucks begin entering a torpor state around November 15 and resume normal metabolic rates around the last week of February. During this time, they may only break torpor about 12 times. As winter breaks, these rodents will seek mates and establish or defend their burrows and surrounding territory.

              Birds also use torpor to conserve energy. Hummingbirds can enter torpor and stay in the state for a few hours. This can help them retain energy reserves on cool late-spring nights or store a bit on energy in cool late-summer nights before they travel south. Whip-poor-wills have also been documented utilizing torpor. They sometimes enter torpor in cool spring and autumn mornings and stay in the state for a few hours.

              Cold-blooded animals can slow their metabolic functions as well. This is called brumation. Some cold-blooded animals, like toads, burrow several feet underground and relax until spring. Others, like the bull frog, wait for spring in deep, cool water. The wood frog can go under leaf litter or into a crevasse and literally freeze. It may have no heartbeat for months. The wood frog lives as far south as Georgia and is the only known amphibian living above the Arctic Circle. Their bodies accumulate glucose and urea, which prevents individual cells from freezing, although the water between cells freezes. Spring peepers will freeze in the winter as well, and, depending on temperature, the first week of March is a good time to start listening for their first calls of the year.