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Notes From The Field Blog

Bird Migrations

Posted: 12/27/2012
Posted By: Robert D. Hinkle, PhD
Original Source: Notes from the Field

migrating drake mallard

They are stirring. Restless, their eagerness building, soon they will come, millions upon millions, as the great migration northward begins. No adjective can enlighten a statement about the enormity of it all, the very diversity of songbirds and the masses that swarm through on starlit nights as they come north, but come they do. And now we can see them, through the darkness, as they push north.

Mysteries of Migrations

Migration seems always to have been a mystery. Biblical references point to the southward movement of certain birds in each autumn. The ancient Greeks thought that swallows flew into muddy stream banks or plunged into lakes and hibernated there for the winter. Other cultures, seeing one kind of birds arrive as another kind departed, believed in the transmutation of species, thinking that one population transformed into the other. At the time of the founding of our nation, it was still believed that swallows migrated to the moon. And yet observations recorded as far back as Aristotle noted the regular and predictable movement of cranes, pelicans and other large, obvious species passing each autumn from northern habitats to spend winter in Egypt along the Nile Delta, only to return in the spring. It seems that throughout recorded history, the seasonal movements of birds have captured our interest and imagination.

Nighttime Migrations

That some species of birds can be seen headed south during daylight hours in autumn makes the concept of migration easy to grasp. But what of night migrants, those elusive "missing migrants" who appear in massive numbers one day and are totally absent the next morning? Anyone outdoors in Northeast Ohio after dark in April and May can answer that question. Listen up, or upwards, perhaps. All through the night, the soft chirps and twitters of migrating birds passing overhead come drifting down out of the darkness. The nighttime northerly migration of songbirds through our region is readily apparent to even an untrained ear.

How Migrating Birds Navigate

Certain species of birds have been shown not just to use stars in migration, but sense and adjust for the movement of stars across the heavens as the night passes. Others appear sensitive to the Earth's magnetic field and use that as an internal compass mechanism to take them northward. Some species have even been tagged with tiny radio transmitters and their signals plotted as they migrated home again. More recently, however, an astounding discovery has been made which allows anyone with access to the Internet or a television to see the amazing scope and breadth of spring songbird migration.

Using Nexrad Radar to Track Bird Migrations

Nexrad radar, promoted unabashedly by television stations, is a network of 158 high-resolution Doppler radars installed and operated by the National Weather Service. Together, they create an overlapping mosaic of radar images, which cover nearly all of the United States. Nexrad is different from other radars in that it can detect precipitation and wind through high-resolution means. Interestingly, it has been discovered that depending on its mode of operation, it can also detect objects as small as migrating insects, and of course migrating birds as well. This first came to light for me three years ago when a remarkable series of Nexrad scans showed the entire ocean between Cuba and Florida blue with the radar images of migrating songbirds. Subsequent evenings showed the migration proceeding northward, until parts dissipated as birds dropped out, returning to their home territories.

Nexrad images showing migration underway can be seen on regional or national radar. Remember that this is an April and May phenomenon as masses of songbirds, migrating in a large front and in mixed flocks rather than "clouds" of birds of a single species, move north. Begin looking just after sunset, when migrating birds, after feeding during the day, rise off their perches to resume the northward migration. The images will first appear as blue "donut-looking" rings, then expand outward and northward as migration continues through the night. Depending on weather conditions and the timing of migration of various species, these images may cover only a few regions along recognized flyways, or they might cover much of the nation as seen here: www.fort.usgs. gov/Radar. For a more technical explanation of Nexrad radar and how it shows migration, check the Clemson University website.

Population Decline

And so they come northward at night, if you read this in late April or May, and you can watch them. While the spectacle is wonderfully revealed through special radar technology, we are reminded that the populations of many of these amazing migrants have declined by as much as 70% in fewer than 50 years. Imagine how the images might have looked in 1940 or so if the technology had been available to see them. Your children's ability to see those images when they reach your age depends entirely on the political, social and moral choices we make in the next quarter-century. All the rainforests on the planet are of no value to migratory birds if their northern breeding forests are too heavily fragmented or missing entirely. Likewise, we share our birds with Central and South America, and without high-quality habitat available there, all the northern forests we save are without value, if you're a migrating songbird. Technology can only reveal, not preserve. The choices remain ours to make.


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