For the Birds Radio Program: Homing, Part II (Original)
(Recording of a Rock Dove)
The homing instinct in birds has been observed for centuries. Ancient Romans made practical use of it–they took nesting swallows from home to games, and then marked the birds with the colors of the winners–the birds would quickly return home to their nests, where the people who missed the games could learn who won. Today that same function is served by TV news personalities–a remarkable example of how man is steadily evolving and may one day be able to do all the things birds never had any trouble doing.
The first serious experiments in homing were made in the early 1900’s. Two ornithologists captured seabirds called noddies and sooty terns from their nests on Florida’s Dry Tortugas and shipped them 850 miles north to Cape Hatteras. In less than six days, the birds were back on their nests, confirming both the remarkable homing abilities of seabirds and the remarkable rudeness of some ornithological studies. The record homing returns are of a Manx Shearwater, another seabird, which was snatched from its nest on Wales and flown by plane across the Atlantic to Boston–it was back on its nest, 3200 miles away, in 12 1/2 days; and of an albatross which was also displaced 3200 miles–it found its way home in only 10 days.
How do birds find their way across these huge distances? Some may use the stars, the sun, or familiar landmarks to navigate by, but not Leach’s Petrel–a seabird that can find its way through darkness and heavy fog. This species may actually use its sense of smell to locate its musky-smelling burrow once it reaches the general area, but how it finds its way over land and sea to get within smelling distance is still not known. Hawks, waterfowl, and gulls, on the other hand, probably use familiar landmarks–like shorelines, rivers, and mountain ridges–to navigate by. Pigeons use landmarks once they are near home, but to begin with they probably use a combination of the sun and a sense of geomagnetism. If the sun is visible, released pigeons quickly orient themselves toward home. But at night or when the sky is overcast, they still usually orient themselves in the right direction. In one study, an ornithologist put non-magnetic brass bars on the backs of one group of pigeons, and magnets of an equal size and weight on the backs of another group of pigeons. On cloudy days, the birds with non-magnetic bars oriented properly, and the birds with magnets oriented randomly. But when the sun came out, they all were able to return to their roosts successfully.
All in all, birds probably use a combination of methods to orient themselves and navigate home. Even with their superior senses of vision, magnetism, and hearing, though, many fly off course every migration, and some birds that people displace from their nest sites never return. Most of the rare birds seen in Duluth every spring and fall are just off-course migrants. Maybe they’re lost, but maybe it’s a natural dispersal mechanism so that if a natural disaster occurs in one place, a species can still survive. Then again, maybe the stragglers are exactly where they want to be, just off to look for America.
(Recording of a Rock Dove)
This is Laura Erickson, and this program has been “For the Birds.”