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Wintry cabin
      (Courtesy NEBRASKAland Magazine/NGPC)

Tracking birds during migration periods
Radar is a powerful tool for tracking movements of flying birds. Migrating birds appear on the radar screen as small targets moving at predictable speeds.

In migration studies, radar has been invaluable in helping researchers determine:

  • direction and speed of mass bird movements,
  • dates and times of departure,
  • height of travel, and
  • general number of birds, especially at night.

One interesting discovery that came out of radar work is that there are relatively large movements of warblers and other small land birds migrating over oceans rather than along coastlines, moving in directions ground-based observers were completely unaware of.

The central flyway

The central flyway

How far birds migrate
or move

Meadowlarks, Blue Jays and Song Sparrows make such short migrations that it's difficult to detect individual movements. Some short distance migrants such as the Harris' Sparrow spend the summer in Canada and the winter in the central part of the Great Plains, including Nebraska.

Long distance migrants such as Common Nighthawks and Cliff and Barn Swallows travel extremely long distances – up to 7,000 miles (11,000 kilometers). Some species of shorebirds fly as far as 8,000 miles (12,8000 kilometers) one way.

Very long distance migrants
Long-distance migration flights are extraordinary feats of physical endurance. Arctic Terns commute about 15,000 miles (25,000 kilometers) round trip each year. Up to 12 million migrants leave the coast of New England in the fall and embark on an eighty- to ninety-hour non-stop flight, traveling out past Bermuda and from there continuing to the coast of South America.

For some tiny birds, like the Blackpoll Warbler, this trip requires a degree of exertion not matched by any other vertebrate. For you to equal what the warbler does, you'd have to run a four-minute mile for 80 hours straight. If the warbler were burning gasoline instead of body fat, it would be getting 720,000 miles to the gallon!

Migrants develop important stores of fat specifically for migration. Fat is great fuel for migrating – it yields two times more energy than carbohydrates or protein. Blackpoll Warblers nearly double their weight from 11 grams to 21 grams before making their big journey.

Even with increased body fat, regular refueling is essential during long migrations. For example, songbirds usually fly several hundred kilometers and then pause for one to three days of rest and refueling. These stopover destinations, or staging areas, are used by millions of birds. Anywhere from five to twenty million shorebirds stop at the Copper River Delta in Alaska every spring. These migrations stops are well-timed – the birds arrive at the same time food becomes abundant.

Migration altitudes
At 20,000 feet you would have a hard time talking while running. But flying geese call to each other even while they travel at the tremendous height of 27,000 feet.

In the Himalayas, observers at 14,000 feet recorded storks and cranes flying so high they could be seen only through field glasses. In the same area, large vultures were seen soaring at 25,000 feet and an eagle carcass was found at 26,000 feet.

One theory about this high flying is that advantageous tail winds of greater velocity are found higher up and that the cooler air minimizes the need for evaporative water loss to regulate body temperature under the exertion of flight.

Radar studies have shown that nocturnal (nighttime) migrants fly at different altitudes at different times during the night. They generally take off shortly after sundown and rapidly gain maximum altitude. They maintain this peak until around midnight, when the travelers gradually descend until daylight.

There is considerable variation, but for most small birds the favored altitude appears to be between 500 and 1,000 feet. Some nocturnal migrants (probably shorebirds) fly over the ocean at 15,000 or even 20,000 feet. Nocturnal migrants also fly slightly higher than diurnal (daytime) migrants.


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