A Novice With Binoculars
The Alula
Tom LeBlanc, Volunteer Naturalist at the Nature Center, showed me a small
black feather and asked me what species it came from.
I finally decided that because of the featherís small size it had to
have come from a small bird. Since
there were a number of the small black-and-white birds around the Center at that
moment, I guessed it was from a Dark-eyed Junco.
Tom told me it was an ěalula feather.î
ěAlula?î I said incredulously, thinking to myself,
ěIíve never heard of that bird.î
But, he went on to explain that the alula is a particular set of
feathers on the wing of a bird and, in the case of this little black feather, it
was from the wing of a raven or crow.
I had never before heard the name and I had not seen an alula
shown or described in any of my field guides that illustrated wing-feather
topography. The alula
(AL-you-lah), plural alulae (-lee), is the group of
feathers attached to a projecting digit (finger) on a birdís wing.
Called the pollex, this
digit is the birdís equivalent to the skeletal parts and muscles of the human
thumb. The numbers of alula
feathers attached to the pollex are variable according to the species.
Some species have only two feathers attached here while others may have
as many as seven.
I now looked with more interest at the small finger-like
part projecting along the front of each wing of our defeathered Thanksgiving
turkey that I had noticed before on many previous turkeys, the finger to which I
had now learned the turkeyís alula is attached. I had never even speculated as to what this appendage to the
Turkeyís wing might be.
Now totally intrigued, I learned that the entire wing of a bird
is termed ěhomologousî to the human arm; that is, it is similar in
structure to a human arm even if its function is different.
The joint at the bend of a birdís wing, which is similar in many
respects to that of our own wrist, gives the birdís ěhandî (the outer
portion of the wing to which the primary flight feathers are attached) much of
the flexibility of the human hand. The
birdís ěhand,î though, has only three digits (fingers) instead of five,
one of which is this feathered ěthumbî
near the bend of the wing. The
other two digits at the outer end of the wing are fused to other ěhandî
bones.
Just as we control our thumbs, the pollex and thereby the alula
can be controlled by the bird independently from the rest of the wing.
The alula is used by a bird to create a slot at the front of its
wing to help channel the air flowing over the wing so as to increase its
ěliftî as the bird slows down, much as the flaps on a modern airplane are
used as it is landing. Without this
part of the wing, the birdís flight would not be nearly so graceful.
Iíve now begun to look more carefully at the wings of close-by common
larger birds such as crows. I had
rarely paid much attention to crows, but now instead of dismissing one as just
another crow and turning away to try to find something more ěinteresting,î I
find myself carefully observing - watching it as it slows down, hoping to see it
ěthumbî the air as it lands.
By: Michael J. DeSha
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