Seeing the Crested Caracara on the 7th piqued my interest in the species.
So far, I found out that -
A) "Cara" in Spanish means face, so I guess that translates as "face face."
(per Karl Stecher, thanks)
Someone besides me was drawn to that bird's "interesting" face when they
named the bird.
B) *The Sibley Guide to Birds* teaches us with both an illustration and
with text, "Color of
facial skin can change in seconds." (page 129, first edition). I was
intrigued by that and tried to find out more about it.
*Lyons, J. 1984. Caracaras in captivity. Pages 69-77 in Wildlife
rehabilitation, Vol. 2. Exposition Press, Inc.; Smithtown, New York*.
"The bare skin on the face of this bird is an interesting and distinctive
feature. When the bird is at rest, preening or being preened, or engaged in
other non-aggressive behaviors, the facial skin is bright orange-red. When
threatened, the color of the facial skin changes to a pumpkin color and
finally to pale yellow. Apparently, threat or fear causes blood to bypass
the subepidermal blood vessels, resulting in a change in facial skin color.
The caracara's crest provides another method for communication. When a
caracara is comfortable and not threatened, the crest lies flat. The crest
is raised when they feel threatened, frightened, or are on alert."
*
*
So caracaras must really "need" to signal stress, and they have two
different ways to do it.
*
*
What the color change is NOT about - not the temp, the mess, not the mate.
The lack of facial feathering is well known in other carrion eaters,
where it both serves
for thermoregulation (for heat dissipation in these blackish birds who
sit in the sun) and also avoids messiness (Don't you hate it when carrion
sticks to your face?).
Facial skin can change color in many birds during mating displays, (Wild
Turkey) or to show that the bird is healthy and eating prey containing
carotenoids (Red-legged Partridges
and European Kestrels).
For more reading about that, see:
http://people.eku.edu/ritchisong/avian_integument.htm
But it is the color *changes* that intrigue me.
I began to think about how rapid mutability of the color of the facial skin
would be adaptive as it evolved, spurred
by a question from SeEtta Moss.
These are just speculations, as I could not find much about just how the
signal is acted on by the caracara that notices it.
Assumptions:
The sexes are similar in appearance, and the color change is shown by both
sexes, so it is not strictly a mating behavior.
The volume of blood diverted from the facial skin would be a trivial amount,
so the rest of the bird would not benefit from its diversion from the face.
(So this is not equivalent to more
blood flowing to a human's gut after eating, during digestion).
The sub-epidermal vessels are usually engorged, which is a signal to other
caracaras that could mean, "I'm an adult Crested Caracara, and I am not
stressed right now."
I doubt that other species of birds or the prey care what color caracara
faces are, so presumably it is a signal only between or among individual
Crested Caracaras.
When the bird is threatened or stressed, etc, the sub-epidermal vessels
constrict, causing the face to become "pumpkin colored" then the "pale,"
within seconds.
The color change would mean to another caracara, "I'm stressed!"
It seems at first blush not to happen fast enough to be the equivalent of
the Blue Jay's scream, "We're
under attack!" or "Let's go get that owl!" But maybe caracaras are very
sensitive to even slight color changes, so the signal could occur with the
first shade of color change, right away, when even a few seconds are too
long. Maybe a signal that takes a few seconds is quick enough.
Just how would other caracaras react to that silent facial signal and to the
raised crest. (I guess the simple answer is a rhetorical question, "How does
any bird respond when it sees that another bird is stressed).
The "I'm stressed" as a signal to other caracaras could mean, "Danger is
near."
Or "Not now, I am too stressed."
Or, "Help me!"
This is as far as I got, and I am eager to learn from others who know more
about it.
I am particularly interested in how other caracaras respond to that color
change, which is the part I am least clear about.
Joe Roller, Denver
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