Hi:
The term “Bird Brain” has been used by human species over the
millennium in a derisive manner, usually implying that someone is as
dumb as a bird. It might be fun to look at just one aspect of a bird’s
biology, its migration strategies, to see if this perception of a
bird’s brain is factual. Let’s focus on the Upland Sandpiper, an inter-
hemispheric migrant shorebird that winters in South America and whose
breeding range includes Colorado. Right now the Upland has left its
wintering grasslands in Argentina and is winging its way north, could
be in Texas in a couple of weeks. So how does the Upland navigate its
way to the grasslands in northeast Colorado? Most likely the Upland
has an imprint in its brain of the general longitude and latitude of
Colorado’s grasslands where it may have successfully bred the year
before, but again how does it accomplish this feat of navigation?
Migrating bird use three orientation strategies assisting them in
keeping on course to a destination.
Magnetic compass: following the magnetic pull from either the northern
magnetic pole or the southern magnetic pole. The receptor for the
magnetic influence in a bird is located in a tiny section of the
retina of the eye also in some species on some skin located near the
upper beak.
Sun compass: depending on the geographic latitude, longitude, and time
of year, the sun will have a varying influence on the bird’s ability
to zero in the relative azimuth of the sun to orient its migratory
direction.
Star compass: this orientation is used mostly by night migrating
species. Because stars in the Northern Hemisphere rotate counter-
clockwise around the Polaris star and clockwise in the Southern
Hemisphere, changing their appearance seasonally as well as
attitudinally, when stars can be seen, they offer a reliable source
for direction.
The Upland may use one strategy or another or a combination of all of
them depending upon conditions. It is quite amazing to think how the
brain of an Upland Sandpiper, leaving its wintering grounds in South
America for the grasslands of Colorado can compute all this incredibly
complex, sophisticated information. We may be able to accomplish this
feat, but we would have to carry around a sack full of expensive gear,
and confusing manuals, to have any hope of doing it.
For more on this topic please see the Auk Vol 126,no 4, October 09
Bob Righter
Denver CO
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