Geolocators give insight to distance migrations

If you’re seeing flocks of ducks or geese in “V” formation heading south, you may think that the fall migration has begun. However, it really began back in July.

Along East Coast beaches, shorebirds that nested in the Arctic began showing up along New Jersey coastlines in midJuly. Snowstorms can blow through the tundra in August, so Arctic shorebirds fledge their young as quickly as possible to get an early start south.

Closer to home, male rubythroated hummingbirds begin heading south in early August. Any hummers you see right now are probably migrants from farther north. At Hawk Mountain in eastern Pennsylvania, redtailed hawks and golden eagles move through in November. Bird migration runs from July through November, depending on the species.

The most impressive migrants are long distance travelers. Arctic terns, for example, have been known for years to make a 22,000-mile round trip to and from the tip of the Americas. Recent advances in tracking technology have revealed other long distance wanderers.

Sooty shearwaters, for example, roam the Pacific Ocean for most of the year. One population, for example, follows a figure-eight pattern that takes them from Antarctica to the Bering Sea. Though they nest in the south Pacific, these long journeys keep the birds in areas where their food — fish, squid and krill — is abundant.

Similarly, Pacific golden plovers nest in far western Alaska and northern Russia. Then they head to wintering grounds from eastern Africa to Australia, Hawaii, and even coastal California. In so doing, they complete a 10,000-mile to 15,000-mile transoceanic migration.

We know about these phenomenal movements thanks to tiny geolocaters that can be attached to captured birds. When the birds are recaptured, the data recorded by the geolocator can be downloaded and analyzed.

Geolocators record a variety of information including the amount of day light, which is used to determine latitude and longitude on a daily basis. Some units also record air and water temperature and depths to which the birds dive to feed.

Tracking animals with geolocator tags is easier and cheaper than using radio telemetry devices. Everything from whales and sea turtles to fish and seals can be monitored. Some units are so small they can be used to track small song birds and even invertebrates.