green on green

Hiding in plain sight by matching the color of your skin to the color of the background is useful for predators stalking their prey or prey trying to escape predation.  It’s also useful in confusing photographers about where to aim their cameras.  Case in point: I saw the bushes moving, wondered if it was a bird, thought it might be a chipmunk, but stared right at the little critter for a full minute before I figured out what it was.

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A gray tree frog in green phase hiding in plain sight.  It wasn’t this obvious without the zoom on the camera to help pinpoint its location.

gray tree frog-

It’s scientific name gives a hint to its ability to change colors: Hyla versicolor. Usually it appears mostly gray with green splotches.

Many species of fish, amphibians, and reptiles have the ability to change color and outward appearance by contracting or expanding the chromatophore (pigment-containing) cells in their skin.  This chameleon-like ability can assist them in better regulating their body temperature, or as suggested, in achieving the kind of camouflage that helps them evade their predators or fool their prey. It is thought that the animals’ eyes perceive the color spectrum of their environment and send neural signals to skin chromatophores to effect the appropriate color changes.

In cases where there doesn’t seem to be a clear message about the color of the background, Gray Treefrogs are often mottled gray and green, or just remain gray, as illustrated below.

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Hmm… water in a bird bath? Not sure what color to be.

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Gray treefrog sitting on the side of a dish pan, next to green vegetation — again, it’s confusing about what color to be.

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Gray treefrog sitting on an orange dahlia — no possibility of a match here.

gray-tree-frog-green-phase

Green-colored Gray treefrog on the ledge of a wooden door? Clearly a bad match.

Blending in… or not

In the winter, everything seems to take on shades of gray and brown, even the several day’s old crusty snow.  When I looked out in the backyard early one morning recently, I saw a few members of the local deer herd wandering down the hill toward the pond, but didn’t think there was much of photographic interest there.  So I just snapped a quick couple of images.  When I finally got around to looking at those photos, I found the deer match their gray-brown background so well, I didn’t even see the large buck having a morning rest in the snow.

white-tailed buck resting

It’s easy to miss even large-bodied animals, like the buck in the left background, when they aren’t moving around.  When the light is dim in the early morning, and the world is gray-brown, whte-tailed deer blend in nicely with their surroundings.

white-tailed buck resting

A little photo “massage” makes the buck stand out a little better.

Most of the gaudy male birds wear their less conspicuous plumage in the winter — to better blend in and avoid being someone’s lunch.  But there’s always an exception to that general rule:

male Northern cardinal - wnter-

Mr. Cardinal doesn’t stay in one place long, and he is obviously the brightest thing visible in this monochromatic (almost) background.  He visits the feeder right at dawn and again at dusk, and stays tucked into dense vegetation during the rest of the day.

female cardinal - wnter

Mrs. Cardinal is less colorful, but she too only visits the feeders at dawn and dusk, when there is barely enough light for me to see which birds are there.

Color me green, or gray, or brown…

Gray Treefrog, Hyla versicolor

The ever-changeable, Gray Treefrog.  How does it do it?

Green is a popular color for frogs, and birds too, but that lovely green color doesn’t come from a green pigment as you might expect, but from the interaction of multiple layers of specialized color and light-reflecting cells in the upper layers of their skin.

Frogs have three layers of chromatophores (color-producing cells) in their skin. The deepest layer are melanophores that produce melanin pigment giving skin a brown to black color. The middle layer are iridiphores which contain no pigment but instead have mirror like plates capable of producing iridescence, or when viewed from a certain angle, reflect blue light. The most superficial layer of chromatophores are xanthophores that contain a yellow pigment.  When the middle layer of iridophores interact with the top layer of yellow-pigment containing xanthophores, you get what elementary school students have learned:  yellow paint + blue paint = green color.

gray treefrog color

A closeup look at the skin of Gray Treefrogs reveals a mottled pattern of color — the result of different stimuli to those color producing cells in the skin.

Animals that change their skin color (like some frogs and reptiles) not only can change the shape and size of the chromatophore but the dispersion of the pigment within the cells.  Thus, tightly contracted chromatophores with no dispersion of pigment might appear white, and the opposite pattern would look black. Moderate dispersion of melanin pigment in the deepest layer of chromatophores looks gray. Dispersion of pigment in the xanthophores coupled with dispersion of light-reflecting particles in the iridophores produces variation of yellow, blue, and green colors in the skin.  Combination of all of the above produces the mottled pattern of coloration the animal uses to blend in with its background — a protective camouflage.

gray treefrog color-closeup

An even closer, close-up look at the skin of the Gray Treefrog.

Color change seems to be temperature dependent:  warmer frogs are lighter in color to reflect incident light; darker frogs are generally cooler and the darker skin helps them absorb heat.  Skin color becomes lighter when these frogs are placed on a brighter background, and darker when placed on a dark background.  This color matching is part of the effective camouflage protection.  And lastly color change may reflect the mood of the animal — e.g., sexual display, territorial display, etc.  The stimulus for all of this change begins in the brain, is transmitted by hormones, and carried out by the actions of the chromatophores — all in a matter of seconds to minutes.

A really detailed and fascinating discussion of how color change is achieved in animals (in this case a Chameleon) is shown below.

Fotogenic Frog

gray tree frog

A dahlia flower fell down into some yews, and a shy tree frog decided it was a fine place to rest.

The Eastern Gray Treefrogs are most often found on vegetation, usually high up in the trees, rather than near water, as their name implies.  Actually, I most often see them in the outdoor tank we use to water potted plants.

gray tree frog

I picked up the lid of the water tank to see if it needed filling, and found this little guy waiting for me. I don’t know how they get in, and I wonder how they get out.

gray tree frog

They are adept at climbing vertical surfaces, even slick ones, using their sticky, enlarged toepads.

Their skin has a warty appearance, like that of toads, and they manage to stay hydrated without taking refuge in pools of water, even during hot days.  Gray Treefrogs tend to hunt at night, often near an outdoor light fixture where they can capture insects coming to the light.

gray tree frog

Interesting eye color in this individual, and you notice patches of green in the otherwise gray skin.

Skin color in these frogs is highly variable (hence their scientific name — Hyla versicolor).  Three layers of chromatophores in the skin (color-producing cells) combine to produce the color pattern, which can change (very slowly) from near white to very dark brown, with variations of mottled green and gray in between. Treefrogs don’t match their environment perfectly the way a chameleon does, but their color changes do help camouflage them in their environment somewhat.  More on how this is accomplished in the next post!  Stay tuned.

gray tree frog

oops, there are no red-orange pigments in those chromatophores, so color matching this dahlia would be tough.

Sooty Grouse in the backyard

I stepped outside the door to go hiking on the Tahoe Rim Trail near sunset, and ran into a family of Sooty Grouse (hen and four young).  For those who know their birds, these used to be called Blue Grouse, and they do have a small amount of blue showing on their breast feathers.  But overall, this bird does an amazing job of blending into its coniferous forest floor background.

Mother hen led her offspring across the road and up into the forest.

Note how well the young grouse blends into the background.

Sooty Grouse live in montane foothills, near the coniferous border, and range from northern British Columbia along the coast to northern California and all along the Sierra Nevada mountains.  They are permanent residents where they occur, but have the strange habit of actually going to higher altitudes in the winter (contrary to most other species).  They are quite omnivorous in the summer, eating a varied diet of insects, berries, and leaves, but in winter they subsist on a diet of Douglas fir, hemlock, and pine needles.  In order to balance their winter energy budget on such an indigestible diet, their gut elongates and they grow a large fermentation chamber in the part of the gut analagous to our appendix (theirs is called a cecum).

To maintain their cryptic coloration in the winter, their newly molted feathers are a grayish white color, so they blend nicely into the winter snow.

In the spring, the male molts new, bright brown and gray feathers, and develops brightly colored vocal pouches on either side of their neck which they inflate while spreading their tail and parading in front of the female.

photo from Avian Web