Day 2B: Peachfuzz
The first
feathers to grow on these babies are called down feathers. Down is fuzzy
and warm, but doesn't look like real feathers yet! Also, notice how these
feathers don't cover the birds' entire bodies. They only grow in special
areas called feather tracts. The very first feathers grow on the back
because the tummy and sides are pressed tight against the nest and the
other nestling. The back is the place where insulation is most needed.
Q: What is a reason why most birds don't grow feathers over their
whole bodies but only in tracts?
(Answer under photo.)
A.
Except
for a very few birds like penguins, who swim in VERY cold water, most
birds don't need to grow feathers over their whole bodies. One individual
feather is a lot wider than one hair, and can cover a bigger space on
a bird's body than one individual hair can cover on a mammal's body.
But feathers take a lot of energy to produce. To save energy, birds
produce just enough outer feathers to completely cover their bodies
when the feathers are groomed properly. An adult hummingbird has only
about 940 feathers on its whole body. That's many fewer feathers than
an adult mouse has hairs!
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