BIRD MIGRATION 
Migration Movement
Well before the autumnal equinox, more than 200 species of migratory birds make their north-to-south journey down the flyways from northern Canada to Central and South America. Known as neo-tropical migrants, these are not exotic strangers but the familiar tanagers, buntings, thrushes and warblers that may have frequented your backyard all summer.
They fly south, not to avoid cold weather, but to find food because insects are disappearing. Shorter days and longer nights in the Northern Hemisphere also put a limit on food gathering.
Nothing interferes with birds' instinct to travel, which may give us the chance to host some new visitors at backyard feeding stations. The question is, will they stay put, move on or move in?
Permanent residents of your local area are known as non-migratory birds: cardinals and chickadees for example. Winter residents, such as white-crowned and white-throated sparrows, breed as far north as the Alaskan tundra but spend the winter locally in places like Hartford, Milwaukee and Coeur d'Alene. Some warblers may be migrants that breed father north, winter farther south, and only pass fleetingly through your neighborhood.
Southbound migrants predominantly are nocturnal, traveling under the cover of darkness to avoid predators. Starting just after dark and ending before sunrise, nocturnal migration generally peaks around midnight. Unfortunately the night travelers can be at peril from manmade hazards -- tall, abundantly lit buildings in spreading commercial developments.
Ornithologists know that bright lights at night confuse birds' navigation systems, causing severe disorientation. Chicago's Field Museum scientists studied the number of bird fatalities at McCormick Place (right), a largely glass exposition hall on Chicago's lakefront, during the prime fall and spring migration periods. In a two-year period, more than six times the number of birds died after hitting lighted windows than died from hitting unlighted ones.
Chicago is one of several big cities to implement a "Lights Out" program. Building managers keep bright lights off in tall buildings to make the skyline darker during September and October, helping the birds pass over the city more safely.
Mystery of Migration
Many of our summer birds -- the neo-tropical migrants -- travel thousands of miles twice each year between their wintering homes in the south and breeding grounds in the north. And even scientists who have spent years trying to solve the mystery of migration don't have all the answers.
Some birds migrate north to south, others east to west. Then there's the wandering albatross, which breeds only every other year. So it can stay at sea for as long as two years at a time, following the ocean currents and prevailing winds in an unending circular migration route around Antarctica.
Some believe that birds have the ability to navigate using the sun or stars as a compass. Others think that land formations, rivers or wind directions play a part. A recent finding alluded to an unusual chemical in birds' eyes that may make them able to "see" Earth's weak magnetic lines of force as if they were an interstate highway in the sky.
It makes sense that many small North American songbirds migrate at night. They are somewhat protected from predators, and they are able to feed during the following daylight hours.
Approximately two-thirds of all North American bird species migrate. This means they travel from a breeding area to a wintering area and back again.
How do birds know when it's time to leave their summer or winter homes? They must prepare for this long flight by molting old feathers and growing new ones, as well as putting on extra fat to fuel their long flight.
Some people believe that it simply is instinct that brings birds north to breed in their traditional summer grounds. But birds also can improve or change their techniques. For instance, as they get older, they learn the most productive areas for food and change their route accordingly.
Many North American migrations are timed so that the young nestlings hatch just as spring seeds and berries ripen and insects arrive. Northbound migrants must time their travels correctly or face winter-like conditions when they return.
The indigo bunting that breeds and raises its young in the northeastern half of the country migrates each fall as far south as Panama. For a little bird that's quite a trip. Although buntings separate into breeding pairs in the spring, during migration they form flocks for their journey.
Within one species in the same state there can be variations in migratory patterns. Some white-crowned sparrows, for example, are permanent central California residents. Other white-crowns migrate from northern breeding grounds to southern parts of the state.
One tiny bird that travels thousands of miles between its summer and winter grounds is the ruby-throated hummingbird. It summers in the eastern half of the U.S. and southern Canada and winters in Mexico and points south.
How a bird, measuring barely three inches in length and weighing only a few grams, is able to fly thousands of miles and still maintain its course against prevailing winds is beyond imagination. And yet, each year this feat is repeated. The hummingbirds, buntings and all of our summer birds return every year to grace our backyards, fields and woods.
Although "neo-tropical" sounds exotic, many of these species are regular visitors to backyards. Purple martins, hummingbirds, warblers, thrushes, buntings, orioles, vireos and tanagers all are considered neo-tropical migrants because most of their populations winter south of the border.
Whether mystery or miracle, this cycle has continued throughout the years. Keeping a bird journal can help you learn a little more about your feathered friends. When the first migrant flies into your yard, mark it on a calendar and jot down some notes. Include any other observations you make on these birds. You could be helping to solve the mystery of migration.
Soaring the Skies
Taking Flight with the Birds
In much the same way as your backyard birds display different eating patterns, you will notice that they exhibit different flying patterns as well. Basic techniques include flapping, gliding, soaring and hovering. Most birds use at least two of these on a regular basis; some birds use all four. For example, the little yellow and black "roller coaster" approaching your feeding station is the American goldfinch, using its characteristic alternate gliding and flapping technique.
Flapping
Flapping is the most common pattern you see. But it also is complex and requires sophisticated wing strokes. The up and down motions are obvious, but the birds also use strong backward and forward motions to propel themselves. On the down stroke, their wings extend and curve for maximum air resistance. On the up flap their wings fold a bit, then quickly rise as the air passes between the separated primary feathers. Before birds developed the strong muscles needed for flapping, they all glided.
Gliding
Today, gliding is used primarily for short distances. Game birds, such as quail and pheasants, will flap quickly to gain altitude when they are startled and then stiffen their short wings and glide silently away. Swallows, swifts and starlings use the glide pattern when descending, which helps them conserve energy. A bird's speed and initial height at takeoff, combined with the wind, determines the length of the glide.
Soaring
You may have heard the expression "riding the thermals." This soaring flight technique is used by birds with large wingspans, taking advantage of wind currents and rising warm air to ascend and travel through the sky. Eagles, hawks and vultures soar because it is energy efficient, allowing them to stay aloft as they hunt for prey for hours without tiring.
Hovering
Hovering is used by birds to hold themselves in midair by flapping their wings sufficiently to stay in place. Hummingbirds are champions of this practice, able to beat their wings 50 to 60 times per second while hovering like a helicopter, then going forward, backward or sidewise. Watching your birds' flight patterns may help you identify species in the air and will add a new dimension to your pleasure of the birds around you.
Flower Power
Birds are tangible reminders of the link between landscape and geography. In the process of moving from one flower to another, birds not only feed, they also pollinate.
Some species travel a migratory trail of thousands of miles, following blooms from distant Central America to North America. The rufous hummingbird, for example, stops in Oregon, California and Colorado en route to Mexico from as far away as southern Alaska, visiting flowers all along the way. It is nature working in concert with the birds to get plants widely distributed.
History of life on earth has been one of movement of species into new areas and their survival success or failure. The fate of plants and birds and humans is naturally intertwined.