By Paul Kerlinger
Unveils the mysteries of poultry migration. Ornithologist Paul Kerlinger writes in a fascinating sort for all chook fanatics. "An very good, renowned, but authoritative explanation." --Library magazine
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Additional resources for How Birds Migrate
Many of those involved in banding are volunteers. Bird banding has its shortcomings and biases. For every bird recovered a distance from the banding site, perhaps a hundred are never seen again. Before the 1950s the recovery rate for banded hawks was 5 to 10 percent because shooting them was legal. The current rate of recovery in North America is about 1 to 3 percent. In some parts of the world the recovery rate is still rather high. Elliot McClure, the dean of American bird banders, reported that just 4 percent104 of 2,486of the Gray-faced Buzzard Eagles banded on Miyako Jima (an island between Japan and the Philippines) were recovered.
Migrating hawks are counted during daylight at hundreds of sites around the world by thousands of hawk-watchers. The thousand or so members of the Hawk Migration Association of North America (HMANA) count migrants as they pass, recording the number of each species in half-hour intervals. Hawks have been systematically counted at Hawk Mountain Sanctuary in Pennsylvania since the 1930s. These counts reflect the upward and downward swings of the Page 31 populations of many species of raptors and are a useful and cost-effective means of monitoring hawk populations over decades.
New technologies evolved, and scientists quickly realized that they could learn more about bird migration by using these new radars. At least four types of radar have been used to study migration, each of which has its advantages and disadvantages: airport surveillance radar (ASR), weather surveillance radar (WSR), tracking radar, and marine surveillance radar. Radar relies on microwaves that are reflected off an object from a microwave transmitter. What the radar ''sees" is the radar-reflective material within a body.