The first winter chill can send even the hardiest humans into a flurry of preparation for the months ahead.

For most humans, that means bundling up before heading outdoors, heating their homes and slightly adjusting their activities. But for others, it means packing up and moving to a warmer locale. These people, often called snowbirds, spend the warmer months of the year in one spot and the cooler parts elsewhere. Many people who call the Northwest home spend their winters in places like California and Arizona to maintain their outdoor-focused, active lives.

Some animals that spend their lives outdoors also make changes to their living arrangements each year. Some make smaller adjustments, like storing food, growing thicker fur and sleeping more. For others, changes can be much more drastic. These animals, like human snowbirds, participate in an annual event called migration.

Migration is a yearly occurrence when an animal, or group of animals, moves from one area to another for predictable periods of time. Some animals migrate up and down a mountain; this is called altitudinal migration. Birds, land mammals, marine mammals, fish and even insects migrate. Some examples: Arctic terns that fly from the Arctic to Antarctica and back again every year to follow the summer sun; gray whales that move from Alaska to Baja California; and salmon that migrate from the ocean to freshwater rivers and streams.

Migration often takes the animal to warmer climates for the winter, but there are other scientific reasons for the move. Those reasons include photoperiod (the amount of sunlight in one day), food availability, hormonal changes and breeding. Scientists suspect that a combination of these factors triggers migration, and the trigger or triggers may be different for every species.

Those triggers may be disrupted by global climate change. Animals may delay migration if temperature cues are incorrect or they may change the migration destination based on the new temperatures or availability of food. The predators of these migratory animals also follow their prey to the new areas.

DO YOU MIGRATE SOUTH FOR THE WINTER?

If you live in the Northwest in the middle of November, you are probably not a snowbird. So what can you do to participate in the annual phenomenon of migration? Explore your local parks or your own backyard and look for animals preparing for winter here in the Northwest and animals in the process of migrating.

Go for a hike: Places like Nisqually National Wildlife Refuge, Point Defiance Park and Ruston Way offer fantastic wildlife viewing opportunities at this time of year. Some animals live there all year long, some come for the winter and some are simply stopping for a rest on their way to other places. Take guide books, binoculars and a notebook to record what you see. Then look up more information about the animals when you return home to find out if they are year-long residents or simply part-timers.

Observe backyard animals: Closely watch the animals that visit your backyard. Migrating animals may stop by to rest in your trees or to “refuel” at a feeder or water source. Other animals, like squirrels, may be busy gathering food for the winter. Keep a notebook of the types of animals you see and what they are doing. Then use that information to make your backyard even more wildlife friendly.

This month’s column was prepared by the staff at Point Defiance Zoo & Aquarium.

On the Web

To learn more about migration, go to these Web sites.

Point Defiance Zoo & Aquarium: www.pdza.org

National Wildlife Federation: www.nwf.org

National wildlife refuges: www. fws.gov/refuges

Audubon Society: www.audubon.org