Winter is a hard time for an animal to make a living. Plants go to seed or dormant, a blanket of snow covers the ground, and many water sources are frozen. Although some animals are able to remain active during the freezing cold months, others leave for warmer climates or take a long winter nap.
* Flying Bird Migration *
Since most birds are built for flight, many simply migrate to warmer locations during winter. Waterfowl, such as geese, ducks and swans, may travel vast distances to reach their wintering grounds.
Most songbirds move south in winter, while a few species, such as mourning doves, chickadees, and cardinals elect to stay. Although there are fewer resources available in winter, there are also fewer competitors, so a small number of bird species can manage to make a living in a frosty climate.
Ruby-throated hummingbirds relocate to the tropics during the coldest northern months. Many birds of prey, such as hawks and owls, migrate in winter, with the exception of the snowy owl. A field guide to birds, such as Peterson's or Audubon, can help you find out which bird species migrate through and which remain in your region all winter.
* Land Mammal Dormancy *
Except for bats, mammals don't have the ability to fly, making it more difficult for them to travel large distances. Some hoofed animals, such as deer and elk, will move southward to wintering grounds, but with human roads and habitations cluttering up the landscape, it is difficult and dangerous for land animals to migrate.
Many mammals will go dormant to save energy during winter. This means that they must build up their fat stores, find a burrow, nest or den, and then enter a state of reduced activity, often lowering their body temperature and their metabolic rate. Black bears go dormant for most of the winter. This type of dormancy is called hibernation. Most small mammals just reduce their winter activity, lowering their body temperature and metabolism for short periods of time, and then waking occasionally to eat. This type of sporadic dormancy is referred to as torpor.
* Where Do Insects Go? *
Bugs are absent during winter. Where do they all go? Insects have a variety of strategies for coping with winter. Some do migrate to warmer climates. The monarch butterfly is a pretty poster child for this option.
Insects often have several distinct stages in their life cycle. Depending on the species, they may overwinter as eggs, larvae or adults and then become active again as the temperature increases. Many beetles pass the winter in dormancy, with their larvae waking to eat plant roots in spring before transforming into an adult. The juvenile nymph stage of the dragon fly spends its winter in chilly lake water before changing into a flying adult. Social insects (Hymenoptera), such as bees, wasps and ants, hibernate for the winter as well.
So although winter wildlife may seem sparse, many animals of temperate climates don't leave when temperatures drop. They are still all around, just lying low until spring returns.
* Sources *
Exploring Nature, "Where Do Animals Go In Winter?"
ThinkQuest, "The Deep Sleep."
US National Park Service, "Migration Basics."