Say Avians May Be Able To See Magnetic Fields
Are birds able to
literally "see" the Earth's magnetic fields? It's a controversial
theory in scientific circles... but researchers say it also appears
to be a likely one.
The Chicago Tribune reports light-sensitive cells in avian eyes
may be able to sense variations between magnetic fields, perceiving
those changes as shadows. In conjunction with an internal compass
-- which relies on tiny metal filings in the cells of many birds,
that "point" in the proper direction -- birds may follow those
variations north or south, depending on the season.
"You must put yourself in the brain of the bird," says
University of Illinois physicist Klaus Schulten. "We might be
surprised, but animals have many types of senses that we just don't
share."
Schulten theorizes birds use these additional capabilities to
guide them on the proper path, along with visual cues such as the
setting sun. Even smell may play a role in how birds are able to
memorize the migratory path, that often spans entire
continents.
Princeton University researchers Martin Wikelski and Richard
Holland conducted a test of their own that appears to support
Schulten's theories... and suggests age and experience are also
factors. They took 30 migratory sparrows from Washington state, and
released them in New Jersey. Younger sparrows flew directly south,
as they normally would along the west coast to wintering spots in
Mexico. Older birds flew southwest from New Jersey.
"The theory is that they have both a map and a compass," said
Holland -- adding the ability to sense subtle changes in magnetism
likely guided the older birds along the right path.
Wikelski agrees. "The way that birds orient themselves in nature
is probably much simpler than we assume," he said. "They use the
one point in their environment that's never changing -- the
sunset."
Schulten believes a protein called cryptochrome -- found in the
eyes of many animals -- may react to variations in light between
magnetic fields, and help guide avians along the proper path. That
sense may work in conjunction with the "magnetic compass" theory
espoused by the Princeton researchers.
"Birds are very good at picking up little differences in shades
that move through their field of vision," Schulten said. "The
magnetic field may act like a filter modifying what they see, like
a cloud floating in the image."
While other scientists still aren't sure of Schulten's findings,
one thing appears crystal clear: humans -- whose brains also
contain magnetite crystals, similar to those found in bird cells --
shouldn't plan on being able to magically find their way in a
similar manner.
"If we do have a magnetic sense," Holland said, "it's probably
weak and not used anymore."