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There are two different coloring patterns
of birds -- those that promote conspicuousness
(scientific term: phaneric) and those promoting
concealment (cryptic). Lesson 3 will discuss
the second type -- cryptic or camouflage
coloration. Let's talk here about the brighter
patterns.
Has your breath ever been taken away by the
striking colors of a bird? We may be somewhat
blind to the many subtle colors and patterns
surrounding us but we still react when we
see the glowing throat of a Broad-tailed
Hummingbird or the brilliant color pattern
of a Western Tanager.
As a photographer I've always been conscious
of color. With computer images now offered
to us everywhere in an unbelievable array
of colors, I've become even more aware of
color. I know that all of the colors seen
in photos are produced by combinations of
red, green, and blue. I don't know how computers
mix colors but, I do know that however they
may do it, the colors seen in feathers are
more varied and impressive than those in
either computer images or color photographs.
For instance, neither computers nor photos
can display structural colors. Some of the
brightest blues and greens seen in feathers
are structural colors, or colors produced
by an effect called Tyndall scattering. We
see this effect in Scrub Jays, kingfishers
and many other birds. The creation of blue
by Tyndall scattering depends on two factors:
a light scattering surface layer and, a black
background. Scrub Jay feathers, for example,
are really black but contain millions of
tiny reflectors. Structural green is produced
when light passes through a yellow filter
before reaching the Tyndall scattering layer.
This same scattering makes the sky look blue
to us on a clear day, instead the black of
deep space. Wow!
Have you ever looked at a magpie and seen
their basic black take on a sheen of iridescence?
Have you ever watched in amazement as a drake
Mallard's head changed from green to purple
and back to green again? Have you ever asked,
what causes this? Keep reading, because I'm
going to tell you.
Birds in peak condition build up extra keratin
on their feathers. Most light passes through
the keratin. However, in bright sunlight,
some light reflects off the surface in two
different wavelengths vibrating in opposite
directions. This reflection produces a false
hue known as interference color. This phenomenon
serves a useful purpose for birds. A male
Ring-necked Pheasant, for example, is dark
and well camouflaged as he skulks through
the underbrush avoiding predators. But his
brilliance is striking as he walks out into
full sunlight ready to impress female pheasants
(and us birders).
Color affects courtship and mating. Many
male birds take on bright colors during the
courtship season. Bright colors and color
patterns signal to the female that the displaying
male is in good condition and likely to produce
healthy offspring. But the male's bright
color is dangerous as well as exciting. A
brightly colored male will have a better
chance of attracting a mate but will be more
visible to predators.
Territorial defense is affected by color
and color patterns. For many territorial
birds, attack on an intruder is automatic
if certain visual clues are present. The
brightness of the colors is often related
to the intensity of the attack. In experiments,
females of a species that were dyed the colors
of males were driven from the males territory,
and males whose feathers were painted a drab
color could often enter another male's territory
and not be attacked. The down side of this
last is that a male with shabby feathers
would probably lose control of a prime territory
and not attract a mate.
Color affects juvenile feeding. The hungry
nestling with the brightest colored gape
will often get a bigger share of the food
brought in by the parents. The relationship
between adults and their offspring is often
based on color and color pattern recognition.
Many adult gulls, for example, have a bright
orange spot on the bill. When the parents
bring food to the young, the young peck on
the orange spot stimulating the parent to
regurgitate food.
I'm reminded that, just a few thousand years
ago, human hunter-gatherers learned through
dances and rituals to align their behavior
with wild animals. For stalking prey and
avoiding predators, costumes and body painting
were designed to blend in with the surroundings.
For courtship and celebrations, costumes
were brightly colored and often outlandish.
This "educational system" allowed
our ancestors to learn the necessities of
survival. Modern educational systems don't
teach us much about survival but we still
dress in bright colors and patterns to stand
out in a crowd, especially during courtship.
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