Imagine waking up one morning and feeling a little feverish. You leap out of bed, panting like a dog on a hot summer day. Passing by the full-length mirror on your bedroom door, you stop dead in your tracks. Your body is padded with muscles so thick you make Arnold Swarzenegger look like the "before" pictures in a workout program. You rush to the breakfast table and shovel food into your mouth as fast as you can, frantically trying to consume twice your body weight in pizza and doughnuts before the day is over.
Sound like some kind of teenager's nightmare? Maybe, but it could also be your daily routine if your metabolism were the same as that of the Ruby-throated Hummingbird. The metabolic rate of these tiny migratory birds is so high that if yours were the same, your body temperature would top 150 °F. To supply oxygen to its supercharged body, the Ruby-throat breathes about 250 times per minute, compared to only 16 times per minute for most people. To fuel their frenetic lifestyle, Ruby-throats must consume twice their body weight in food each day. For humans, that's about 6,000 calories per hour, 24 hours a day.
The darting image of the Ruby-throat buzzing around the nectar feeder in your backyard represents just a small part of this migratory bird's fascinating life. When hummers leave your neighborhood in early fall, they begin a journey that will take them to the wilds of Mexico. Along the way, many will make a 26-hour nonstop flight over the Gulf of Mexico, an amazing 400-mile voyage across open water.
This brief glimpse into the life of the Ruby-throated Hummingbird is just a sample of the excitement that awaits you when you begin to study birds. Birds are everywhere. They inhabit our cities and the countryside. They are often the most conspicuous and abundant wildlife in our neighborhoods. They are easy to see and observe, and birds have fascinating lives that will introduce you to a whole new world of animal behavior and ecology.
Birds of Two Worlds
In winter, there are typically only about one-half as many species of birds in your schoolyard as there are during the remainder of the year. Where do they go?
Slightly over 600 species of birds nest in the United States; of these, 338 are classified as Neotropical (New World tropics) migrants. This means that during the nonbreeding season (our northern winter) they migrate to the tropical regions of Mexico, Central and South America, and the Caribbean. Some birds, such as the Ruby-throated
Yellow Warbler, Male.
Hummingbird, Golden-winged Warbler, and Blackburnian Warbler, are complete migrants, meaning that nearly all members of the species travel to the Neotropics. In partial migrants, such as the American Robin, Yellow Warbler, and Eastern Bluebird, only some of the population makes the complete migration; others linger further north, depending on weather conditions.
Those migratory species that are not Neotropical migrants display a wide range of migration patterns. Most move from northerly to southerly areas, often within the boundaries of the United States. Some birds, such as the Mountain Bluebird, are altitudinal migrants. They nest at higher altitudes during summer, and retreat to lower altitudes during winter.
Why do birds migrate? Ornithologists believe it is a strategy to take advantage of optimal conditions at two critical times during the birds' annual season. Neotropical migrants come to the Northern Hemisphere to take advantage of long days, good weather, and reduced competition with other birds. Mostly, however, they come to feast on the superabundance of insects needed to feed their young. As days shorten and the weather turns bad, migrants return to the tropics, where stable temperatures and adequate food sources prevail.
Many Neotropical migrants undergo dramatic shifts in ecology and behavior as they migrate from north to south and back again. Imagine the changes that a young Blackburnian Warbler experiences the first year of its life. Hatched in the spruce and hemlock forests of the northeastern United States, the nestling consumes a steady diet of caterpillars and other insects brought by its attentive parents. Late in the summer, it begins a 5,000-mile journey to the humid forests of the South American Andes without the benefit of prior experience or other, more seasoned birds to guide it. Once there, its diet shifts to include not only insects, but also fruit. Like many migratory birds, the Blackburnian Warbler's plumage also changes. Its muted nonbreeding-season feathers are transformed to fiery orange by springthe better to attract a perspective mate. On the warbler's first night in South America, it may fall asleep listening to the howling of monkeys, which is a far cry from the raccoons and red squirrels that were its neighbors in its breeding grounds.
