Radar, fast becoming a must-have tool for ornithologists, is capable of revealing the highs and lows of bird migration—within a few feet. The newest weather radars can even distinguish between birds, bats, insects, dust, and pollen.
Jetliners: 35,000 feet
Bar-headed geese: 29,000 feet
The highest flier, the bar-headed goose, has been sighted over the highest Himalayan peaks, forgoing lower mountain passes. Swans have been seen flying at 27,000 feet.
Raptors: 22,000 feet
At 20,000 feet, birds breathe where mammals can't, thanks to a complex respiratory system that sends a continuous flow of oxygen through their lungs.
Many long-range fliers rise from 5,000 up to 20,000 feet during migration, gaining height as they burn fat and lose weight. The distance champ is the the Arctic tern, with a 13,000-mile trip between polar regions twice a year.
Waterfowl: 16,000 feet
Nocturnal migrants—most songbirds and ducks—take advantage of less turbulence and fewer predators while gaining feeding time during daylight hours.
Small planes: 8,000 feet
Songbirds: 6,000 feet
New radar data show that when songbirds migrating over the Gulf of Mexico hit strong headwinds, they drop to low altitudes. In the future they will risk collisions with wind turbines.
Sandpipers: 3 feet
Some migrants, including sandpipers and sea ducks, skim the water so closely that they disappear behind cresting waves.