Biology Reference
In-Depth Information
trip north in spring, and then are on their own. Most birds, however, cannot depend on
theirparentstoleadtheway.Younghummingbirdsandloonsmigratedaysorweeksafter
their parents have left, and yet the young birds know which way to head, how far to go,
and when to stop. The more we study the intricacies of orientation and navigation, the
more miraculous it seems.
In some cases, birds head in one direction for a certain distance and then change
course. For example, Blackpoll Warblers start their migration in an easterly or southeast-
erly direction from Alaska and northern Canada toward the Atlantic coast. They bulk up,
often doubling their weight, and then strike out over water on a journey that can take
from36to88hourswithoutasinglebreakforfoodorrest,traveling1,500to2,200miles
(2,414 to 3,540 km) nonstop until they reach South America. They start out over the
ocean heading southeast, aided by northwesterly winds. As they approach the Tropic of
Cancer, they start encountering the northeast trade winds, which deflect their flight to the
south or southwest and provide favorable tail-winds as they make the final push toward
South America.
Inthiscase,favorabletailwindsmayhelpsendthebirdsintherightdirection,butthey
can use other navigational aids as well. Research scientists are teasing out the environ-
mental cues long-distance migrants use, including the earth's magnetic fields, the move-
ment of stars in the sky, and polarized light patterns. Recent research has discovered a
neural connection between the eye and a part of the forebrain that is active during mi-
grational orientation. This suggests that the visual system is involved in the birds' ability
to sense the earth's magnetic field. Some species may also use visual landmarks, such as
mountains or rivers below them.
ADOPTIVE PARENTING
Beginning in 2001,
a population of captive-reared Whooping Cranes have been
learning their migratory route by following an Ultralight aircraft driven by crane-cos-
tumedhandlersthatthebirdsareimprintedon.ThebirdsfollowthetinyplanefromWis-
consin to Florida their first autumn, then make the return trip and subsequent journeys
entirely on their own. Eight years after the first release, some of the birds are starting to
breed, and ornithologists hope that soon this introduction will be providing a self-sus-
taining population of this endangered species.
