How do migrating birds travelling thousands of kilometres find their way? This has been a much studied topic in recent years. The more the question is studied, the more the complex the answer appears to be.
It has been observed that many more birds make migratory flights when the sky is clear than when it is cloudy, leaving scientists to conclude that the sky must be a navigational aid. Studies conducted in planetarium type buildings have verified that birds can indeed orient themselves to the sun or to certain star formations. It has even been determined that they have some sort of internal clock that allows them to compensate for the movement of the sun (or stars) as the day (or night) passes. But some birds were observed migrating during poorer whether when no sky was visible at all. How did they know which way to go?
Some birds apparently use a combination of factors. A study involving Blue-winged Teal showed that they had the ability to use familiar landmarks to determine their direction and then orient themselves relative to the wind. They then flew such that the wind remained in that same relative direction (works fine as long as the wind doesn’t change direction en route).
Experiments with some species of pigeons indicate that they have built-in compasses which allow them to detect the earth’s magnetic field. When tiny magnets were affixed to their heads they became totally disoriented. There is also evidence to suggest that some birds can hear extremely low frequency sounds, such sounds can be heard over very long distances. A bird flying north through the prairies might be able to here the wind in the Rockies off to the left and the waves pounding on the coast to the east. Some birds apparently use much more “low-tech” methods, they merely follow coastlines or major river valleys.
While all of these methods would be of assistance in determining general direction, none are specific enough to allow a bird to return to the same small lake or the same field or the same nest in the same tree year after year. It would seem that the navigational aids get them close and then memory and familiar landmarks do the rest.
But how do we explain some birds’ ability to get “home” under circumstances other than traditional migratory flights? How do homing pigeons get home? Experiments have been conducted with birds other than pigeons. One such experiment involved a Laysan Albatross removed from its nest on Midway Island west of Hawaii and released in Washington State. Ten days later it was back on its nest, having made a 5,000 km journey across a featureless ocean. It is not completely understood how birds can navigate across unfamiliar territory in unfamiliar directions. Research continues.
