Spring Migration

Joe Meche is a past president of the North Cascades Audubon Society and is still active in chapter affairs.He has been watching birds for more than 50 years and photographing birds and landscapes for more than 30 years. He has written more than 100 articles for Whatcom Watch.

In 2001, the popularity of the award-winning documentary film, “Winged Migration,” was widespread and made more people than ever aware of the spectacular natural phenomenon of bird migration. It’s a phenomenon that has taken place like clockwork long before humans were here to invent clocks. Millions upon millions of birds take part in migration in the spring and fall in response to their individual needs and the changing seasons. Of these immense movements, spring migration is perhaps the more heralded of the two. The massive movement of birds in spring is the beginning of a new year. It’s the cyclical time of year for birds to engage in their often elaborate courtship rituals, leading to breeding, nesting, and raising the young of the year.

After a quick check of the calendar in early March and springing our clocks forward, the time has arrived! Birdwatchers everywhere are in the early stages of euphoria because it’s time once again for the annual spring movement of millions of birds from their winter retreats to their breeding grounds. Early signs are already upon us locally that the southern contingent of birds is already on the way north with the arrival of tree and violet-green swallows. These small, active birds are the true harbingers of spring in the Pacific Northwest.

Many of the birds that have wintered here and farther south are in the process of staging in local waters. These birds utilize the biologically-rich, protected bays and inlets to rest and to feed and forage. The time they spend here is essential to build their fat reserves for the long journey to their respective breeding grounds. The loons, grebes, scoters, and other birds that winter on saltwater and nest farther inland to the north and east require these energy reserves to fuel their arduous flights over the mountains to freshwater lakes and ponds.

In some respects, there are mixed emotions when the birds that we enjoy throughout the winter leave for the spring and summer months. However, any sadness that we observers might feel is quickly supplanted by the arrival of brightly colored, song-filled birds that have only just begun to entertain us for the next several months. The resplendent wood warblers, thrushes, flycatchers, and more will be the birds that we pursue and enjoy on the longer days that also bring the promise of better weather for the winter-weary among us.

The evolution of bird migration is similar in some respects to the large-scale movements of mammals. When the seasons change and food becomes scarce or fresh water freezes, survival is the motivating factor. Some birds are equipped to withstand colder winters and their basic food and shelter requirements are usually available through the snowy months. The seed eaters, for example, are usually able to find sufficient food throughout the year. Other birds, especially the species that depend on insects, need to move to wherever their primary food sources are available. Follow the food and you’ll find the birds.

We usually think of migration as a north-south movement but elevation also plays a role in the movements of certain species. While they are not considered as migratory, varied thrushes are prime examples of birds that will follow the snowline down to sea level when deep snow in the mountains covers most of their ground feeding areas. Locally, there have been fewer varied thrush sightings this past winter, due to the higher snow levels throughout the area.

In North America, migrations take place along four principal routes – the Pacific, Central, Mississippi, and Atlantic flyways. Traditionally, these are the main north-south corridors where avian movements have taken place. Most of the waterfowl and many sparrows and finches that migrate annually do so completely in temperate North America. But more than 300 species, including warblers, flycatchers, swallows, raptors, and shorebirds winter in the Neotropics.

While many of the local migrants go unnoticed for the most part, there are species that we are more attuned to than others. The spring arrival of Vaux’s swifts has become a well publicized and well attended event all along the Pacific Flyway. Many of the festivals that take place along the coast are part of the celebration of specific migratory birds, like the Pacific black brant and the variety of shorebirds that stop by on their journey northward for their short but active breeding seasons.

In all fairness, it’s important to point out that many birds — many of the smaller species for instance — are nocturnal migrants. The idea of millions of birds migrating at night merely adds to the air of mystery surrounding avian migration. In general, it’s considered that the smaller, ground feeding birds must utilize the daylight hours to feed on insects they find on foliage, leaving only the hours of darkness to continue their migration.

While innumerable studies have been conducted, many are still underway to determine how birds are able to find their way from place to place during migration. Their faithfulness to traditional paths leads researchers to a number of theories about the techniques that birds use. Some birds utilize the sun to find proper direction while others appear to have built-in magnetic compasses that allow them to continue their movement even on cloudy days. Night migrants that orient themselves by the stars might become disoriented on cloudy nights, which might account for our own sightings of rarities along the way.

Humans have become aware of the seasonal movements of birds and used that knowledge for a variety of pursuits. Subsistence hunters rely on the seasonal movement of birds, much as they might on the return of salmon to their native streams. Researchers also rely on traditional migratory routes to further our understanding of this great mystery. Migrating birds are easily snared in safe mist nets where they are given a scientific once-over before being banded and released. Population studies of birds are enhanced by knowing where the birds will be.

In all, bird migration will always be the subject of study and wonder as we continue in our attempt to unravel the mysteries surrounding it. No matter how much we learn about the how and the why, nothing will make it any less fascinating. The seasonal arrivals and departures of hundreds of thousands of waterfowl every year when I was growing up in southwest Louisiana will always be firmly etched in my memory. The sights and sounds of migrating waterfowl still evoke strong feelings from that early exposure to an awe-inspiring part of nature’s grand design.