Migration is one of the most fascinating and least understood aspects of bird behavior. Each species of birds has developed its own reasons for or against migrating. Birds need to have a suitable environment for the 2 or 3 months they are breeding and raising a family, and the rest of the year they basically just need food and shelter until the next breeding season arrives.
Birds that remain all winter in the snow belt have developed strategies that enable them to survive the harsh conditions. The main food sources available in winter are seeds, berries, insect eggs and pupae. Our winter birds use these sources of food and are able to find shelter in tree cavities, evergreens, brush piles, etc. The foods we provide at our feeders supplement these natural sources. It is also important to plant berry bushes, create brush piles, and leave cavity trees standing.
It is easy to understand why some birds cannot winter here when you look at their food sources. Swallows and swifts live mainly on flying insects, hummingbirds drink nectar and gather small insects from flowers, shorebirds and other waterfowl must have open water, and warblers, flycatchers, and most wrens and thrushes are nearly 100% insect eaters. All of these birds must go south to a warmer climate.
Some migration flights can be quite dramatic, while other birds are called irregular or medium-distance migrants. Ruby-throated hummingbirds fly hundreds of miles nonstop over the Gulf of Mexico and lose up to 1/3 of their body weight in the flight. Many Canada geese fly just far enough south to stay in open water. Much of migration is accomplished at night with daylight hours used for resting and feeding. Most small songbirds fly at 20 to 40 miles per hour, while ducks and shorebirds fly between 40 and 60 miles per hour. Songbirds travel between 30 and 200 miles per day, often at altitudes near 4,000 feet. During cloudy nights, they may fly just over treetop level and unfortunately often collide with tall buildings. Most birds fatten up before they leave. The Blackpoll Warbler leaves in the fall with twice the weight it arrived with, and has enough "fuel" to fly nonstop over the Atlantic from Newfoundland to its winter home in South America.
There is much to learn about bird migration, and much that we will never understand. The beauty of birds is not only in their appearance and their songs, but also in the fascinating ways they behave and live their lives.
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