Almost every day after each
of the World Bird Sanctuary Stone Zoo bird shows,
one of the staff gets asked how much Norbert our
Bald Eagle weighs.
Norbert, the Bald Eagle (photo: Sandra Lowe)
Usually we respond with a
question, asking kids and adults how much they think he weighs. The answers are almost
always higher than 20lbs, because most people
don’t understand bird anatomy (Norbert weighs just 7 pounds).
The reason for this faulty
weight perception is twofold; the first is something that’s not visible to the
naked eye. Unlike we mammals,
birds have hollow bones! The
second reason is one that we can easily see, but usually don’t take into
account when doing our weight calculations—feathers! Feathers are very lightweight—even though there may be
several thousand of them on a bird such as an eagle.
Let’s talk about
feathers--that amazing adaptation that gives birds their beauty, insulates them
from the heat and cold, and most importantly—allows them to fly. (Of course, there are some flightless
feathered birds, but that’s a discussion for another day.)
Flight feathers are common
to the majority of bird species. Birds’ feathers will help to
catch air, which allows them to stay in flight. Their wings allow them to direct the air so that they can
create lift. They also will use
their wings to flap, soar, and hover, but that depends on what their wings are
built for.
Diablo, a Tawny Eagle, has passive soaring wings (photo: Aurora Potts)
There are four different
wing shapes. The first one is
Passive soaring wings, which means these birds have long primary feathers (the
outermost feathers on the wing).
These long feathers, with slots between each of the outermost five, allow these birds to catch the upward movement of vertical columns of hot air called “thermals” and to
fly higher in the sky. Some examples
of these birds are eagles, hawks, and storks.
The second type of wing is
the Active soaring wing. This
means that these bird wings are narrow and long, allowing them to soar for long
periods of time on horizontal wind
currents. Examples of these birds
are gulls, albatrosses, and gannets.
Another type of wing is
the Elliptical wing. These wings
are very good for a short burst of high speed flying. Crows, ravens and sparrows are some examples of birds that
have Elliptical wings.
This American Kestrel is a good example of High Speed Wings (photo: Gay Schroer)
The last type of wing is
the High speed wing. The birds in
this category have long narrow wings, which allow them to fly very fast for a
long period of time. Swifts,
ducks, falcons and sandpipers are some examples of these birds.
As mentioned above, although
all these birds are very different, they all have one thing in common... hollow bones, which allow
them to be lightweight. This is a
key factor to why birds are able to fly.
Since birds are so lightweight, wind does tend to affect them while they
are flying.
Riley the Barn Owl (photo: Aurora Potts)
At WBS’s Stone Zoo bird
show in Boston we definitely have windy days
that have affected our birds. For
our Barn Owl, Riley, wind can cause him to have to flap harder and longer to
fly through the wind to get from one trainer’s glove to another. Diablo our Tawny Eagle does sometimes
get blown off course of his flight pattern on
very windy days, but because he’s physically fit from all the practicing we do
with him, he always fights through the wind to
come back. Our Red and Green Macaw Rio actually is the exact opposite of my other two
examples; she would rather wait for the wind to die down, then fly.
Rio, the Red & Green Macaw (photo: Aurora Potts)
Those windy days can
definitely make bird shows very interesting.
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