Some species are no longer visible, but that's not necessarily because they left the area. Others may be even more visible, depending on what's available in your yard.
"Winter is a lean time for all wildlife," says Washington Department of Fish and Wildlife (WDFW) biologist Chris Anderson. "It's the season that naturally helps keep wildlife population levels in check and in balance with available habitat. To survive, animals exhibit different behaviors, strategies, and activity patterns, based on their biological needs."
Anderson notes that the behavior most commonly seen by most people is migration. For some species it makes more sense, from an energy-efficiency standpoint, to migrate out of one area, where winter conditions make food more scarce, to another area where food remains plentiful.
Many birds do just that, most in large groups that are highly visible in fall and spring. Others move out in smaller family groups. Osprey will head south to California or all the way down to Argentina for more favorable climatic conditions to rest and fish. Two of our 15 species of bats -- hoary and silver-haired bats - also migrate to warmer climes.
Some non-winged, land mammals also migrate, although it's more "vertical" - moving from higher elevation summering grounds to lower elevation wintering areas. Elk, deer, and moose are the most obvious examples; as prey species, they are followed by carnivores like cougars, coyotes and wolves.
Many animals go into hibernation, where their metabolism slows down in order to exist largely on stored fat for the winter. Most of our bat species hibernate. Their body temperature, breathing, and heart rate drops. They occasionally come out of this state to eliminate waste, lick condensation from their fur for a drink, or even go out and hunt insects if warm spells are conducive to insect activity.
Bears also hibernate. Their metabolism slows and they go into a sleep-like state, although their body temperature doesn't drop so much. They are in their den avoiding the stressful winter, living off the fat they accumulated when the vegetative bulk of their omnivorous diet was abundant. Bear sows are pregnant when they go into their hibernation den, and will birth their young in late winter in the safety of that den.
Many frogs, snakes and other amphibians and reptiles find areas within their preferred habitat to stay out of the "freeze zone". These areas include the bottom of a pond that does not freeze totally, below rock piles, in rocky cliffs, and under large trees and snags. They go into a reduced metabolic state known as "brumation" - the equivalent of mammalian hibernation for cold-blooded reptiles and amphibians.
Many animals use dormant periods of decreased activity, with reduced body temperature and metabolism rate, known as "torpor." It's a way for some animals, from mice to birds, to eke through a physically stressing period of extreme temperatures or reduced food availability. This can be for just one very cold night, the entire winter, or in overly hot situations.
Anderson notes many people who manage year-round habitat on their property see some wildlife species mostly or sometimes only during the winter. For example, seeds from that alder tree in the backyard are now drawing dozens of pine siskins, many which are year-round residents that are more dispersed in the summer and not usually seen in such concentrations except in winter.
"Providing high quality year-round habitat, both on your property and on others' by working with local habitat enhancement groups, is one thing you can do to help wildlife weather winter," Anderson said.
"Another crucial thing we can all do is avoid disturbance of these animals during these energy-stressed times, including migration, hibernation, and feeding and resting on wintering grounds," Anderson said. "Leave them be, respect their space and needs, and be their advocate!"
Learn more on how to provide habitat and promote wildlife on your property at http://wdfw.wa.gov/living/attracting/ .