May 7, 2020

How wild animals survive the winter in Sonoma County

Hibernation involves a complete change in a bear’s metabolism, helped by a slower heartbeat and reduced breathing, which conserve energy.

But, surprisingly, bears maintain a warm core temperature, only several degrees lower than normal, by burning up their stored fat.

Mountain lions and bobcats don’t fatten up before winter, so they need to keep hunting in colder months, Nelson said. In winter, they seek shelter out of the weather in rock crevices, caves and covered spaces at the base of rocky cliffs.

Alternate strategies

Bats have a completely different strategy — huddling together, said Trish Tatarian, who runs Wildlife Research Associates, a local biological consulting services firm, with her husband Greg. The couple conducts in-depth wildlife surveys and provides ecology assessments for government programs and business projects.

Sonoma County has twelve resident bat species. “Rather than hibernating,” Tatarian said, “bats handle the coldest months by roosting in carefully selected ‘hibernacula.’” These are roosting spaces that provide shelter from the elements, have the right ranges of humidity and temperature and have enough room for large groups of bats to crowd together.

“Huddling closely helps preserve some body heat,” she said. Between October and March, the number of insects — bats’ food — declines, so bats enter a twilight state, called ‘torpor,’ she said.

Unlike hibernation, torpor is a temporary state. The bat’s metabolism and heart rate slows and its activity declines. Their body temperature can fall dramatically, by 24 degrees or more, which saves energy. The little mammals can remain in the torpor state for hours or weeks and rouse when conditions improve.

Some small rodents and birds, as well as some snakes and bees, employ the same torpor state to wait out cold snaps, heavy rain or even limited food supplies. Rattlesnakes and garter snakes gather in dens to wait out the winter, Tatarian said, which is why you won’t see them on trails now.

Ground squirrels and pocket gophers burrow underground before entering torpor, since it leaves them defenseless against predators. Pacific tree frogs will burrow under leaf litter.

Moving south

Hundreds of bird species wing through Sonoma County to migrate for the winter to warmer environments, sometimes thousands of miles away. In the fall, we see monarch butterflies, which are drawn by instinct to fly south from northern locations where they’ve been feeding all summer. Some settle in trees near the coast here or continue to Monterey or Mexico to huddle together by the thousands for warmth, until the seasons change.

Other creatures stay closer to home — perhaps your home. Ants, mice and rats will often seek shelter at this time of year by moving under our homes and other structures, as many local residents can attest.

Of course, cold, rainy weather isn’t a challenge at all for a whole crew of creatures, said Dr. Wendy Trowbridge, director of Restoration and Conservation Science Programs at Laguna Foundation.

“Winter is an opportunity, too.

There is enough water in the creeks for salmon and steelhead to head upstream to spawn. The additional rain connects once-isolated pools together and brings more food and oxygenated water to our resident fishes.”

Trowbridge said after the last round of rains, she spotted four river otters enjoying the additional water in Piner Creek, playing and swimming.

Trish Tatarian of Wildlife Research Associates celebrates the emerging activity as the winter rains descend and newts, endangered tiger salamanders and red-legged frogs appear.

You might see some of this cold weather activity the next time you’re on a winter walk. But, like many of us, wild animals have tucked in and bundled up, awaiting spring.

Stephen Nett is a Bodega Bay-based Certified California Naturalist, writer and speaker. Contact him at

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