Biology Reference
In-Depth Information
learnedthatsomeneuronsinvisualcentersofthebrainrespondtochangesinthemagnet-
ic field. In darkness or red light, these birds may become disoriented, but in white, green,
or blue light their sense of direction is normal.
In 2004, a European team studying the Garden Warbler discovered light-sensitive pig-
ments in the retina that influence how the bird's sensory cells react to the magnetic field.
It's possible that the curvature of the retina and the position of the magnetite in the nares
(nostrils) may create some sort of pattern as they respond to the magnetic fields, perhaps
producingavisualcolorshiftwhenfacingnorthorsouthbutnoteastorwest.Thiswould
explain why birds grow disoriented in some colors but not others, but we don't know if
the birds' perception of magnetism is through vision or some other sense that we mere
humans can't even imagine.
Q How do scientists know that birds use the stars for navigation?
A
Fascinatingresearchprojectsconductedinplanetariumswerebeguninthe1950s,when
European scientists Franz and Eleanor Sauer discovered that Garden Warblers fluttered
away from the projected North Star, even when the projection was rotated to place the
North Star in another direction. During the 1960s, American scientist Stephen Emlen
showed that birds don't recognize one particular star but actually the pattern of stars re-
volving around the one fixed star. He raised young Indigo Buntings in a planetarium,
under a projected sky with stars revolving around Betelgeuse. During the birds' first au-
tumn, they oriented to fly away from Betelgeuse.
Apparently young birds spend part of the nighttime awake, gazing at the night sky.
They seem to notice that the stars move in a circular pattern, and instinctively know that
the one fixed star that never moves is “north,” and they can find it by learning the pattern
of the stars around it so they can figure out where north is even when the sky is covered
with patchy clouds.
Millions of migrating birds strike high-rise buildings every year. What can we do?
Toronto's Fatal Light Awareness Program (
FLAP.org
) patrols downtown Toronto in
early morning to rescue live birds and collect dead ones. They urge people to turn off
lights or close drapes during migration. Chicago, Minneapolis, and San Francisco have
similar programs.
