Bird Migration

By Jackie Canterbury

Imagine the brilliant Rufous Hummingbird during a summer moment, resting in your yard after sipping flower nectar, preparing to migrate across several states. Or the Violet-green Swallow flying low over an open field in search of insects with her flock maneuvering to keep the pace, fattening up for the long journey as far south as Costa Rica where she will spend the winter. Or the Western Wood-Pewee tucked in our PNW forest sallying for insects and bound for northern South America. Tonight, the conditions are perfect for the flight south, the route ingrained. In the West, mountain ranges funnel travel south to varied destinations. The Rufous Hummingbird makes a clockwise circuit moving up the Pacific each spring and as early as September, fliessouth down the chain of the Rocky Mountains, headed for Mexico. For most songbirds, this takes place under the cover of darkness which provides calmer atmospheric conditions and guidance from the stars. Raptors, cranes, and waterfowl travel by day.  

Rufous Hummingbird, photo by Jackie Canterbury
Western Wood-Peewee, photo by Jackie Canterbury

In North America, 70% of birds migrate. Some traveling from the Arctic to the southern tip of South America.  The bird that has the honor of being the longest migrant is the Arctic Tern, who travels 25,000 miles every year from the highest to lowest latitudes. 

Violet-green Swallow

Why do they do it?  Over millennia, birds have evolved patterns and timing mechanisms that stimulate them to fly. As daylight hours shorten and food resources dwindle, hormonal changes urge them to migrate. A pattern called Zugunruhe, a German word for migratory restlessness, has been observed in captive birds for hundreds of years. Caged birds would predictably become restless just before the time they would begin their seasonal migration.

Arctic Tern, in Iceland

Scientists are learning more about migration as a result of advances in the use of weather radar which produce images of millions of birds during migration. BirdCast is a dashboard that explores nightly migration in each state. Here’s Jefferson County’s: This is a critical time for conservation. Some three billion birds have disappeared from North America in the past 50 years, and migrant species have suffered significant losses, no doubt due to their perilous migratory journey and habitat loss in both breeding and wintering areas. We can all help birds by keeping outdoor lights out during both spring and fall migration. Artificial light pollution can attract, confuse, and disorient them. We can also plant for wildlife and provide water features and a hospitable environment for our feathered friends.  Where would we be without them?