Biology Reference
In-Depth Information
American White
Pelican
31
years
Mourning Dove 31
years
Sandhill Crane 31
years
An American Robin can produce three successful broods in one year. On average
though, only 40 percent of nests successfully produce young. Of those that fledge, only
25percentsurvivetoNovember.Fromthatpointon,abouthalfoftherobinsaliveinany
year will make it to the next. Despite the fact that a lucky robin can live to be 13 years
old, the entire population turns over on average every six years.
Q Why don't birds fall off branches as they sleep?
A
Whenabirdbendsitslegstoperch,thestretchedtendonsofthelowerlegautomatically
flex the foot around the branch and lock it in place. This involuntary action is called “the
perching reflex.”
Coping with the Cold
Q How do birds stay warm all winter, especially when the temperature is below
zero?
A
Birdbodiesarelikeawell-insulatedcabin.Theirouter,or
contour
,featherskeepmois-
ture and wind out. Their inner, or
down
, feathers trap air, providing insulation to hold
their body heat inside. Northern birds grow additional down feathers during the fall as
temperatures start plunging. When they sleep, they raise these feathers, maximizing their
insulation just as we do when we plump up a down sleeping bag or jacket.
Even the most well insulated cabin can be darned cold without a heat source within.
Birds have two “furnaces” — their own muscle activity and their metabolism. Both burn
calories from their food to produce heat. Birds can survive northern winters only if they
can get enough high-energy food to maintain their body temperature. This is especially
tricky because the farther north they are, the longer the nights, so the less time each day
can be spent searching for food to stay alive over the long night.
