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.

gray tree frog-

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.

gray-tree-frog-

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.

Toxic toads

I heard a few faint, froggy croaks coming from the dying perennials in the garden.  It seemed a little late in the season for the local amphibians to be active.  But wind and coolish temperatures didn’t deter an appearance by this little American Toad — hiding in the litter under the aging peony vegetation.

American Toad

It’s not much bigger than the chunk of mulch it was sitting on (about 2 inches long). 

American Toad

Not the most attractive skin with its lumps and spots, but those large lumps right behind the eyes (called parotid glands) are the toad’s secret weapons.

Amphibian skin is really quite special.  It can absorb water like a sponge when its owner is dehydrated, and it can secrete a variety of chemicals its owner might use for defense.  Poison dart frogs aren’t the only amphibians to use toxic chemicals to deter predators; several Toad species (in the genus Bufo) secrete a combination of chemicals called “bufotoxin”, which induce a variety of debilitating reactions in animals that try to eat them.  Although concentrations of bufotoxin vary from species to species, one website claims that “the skin of an average-sized toad can cause significant symptoms and even death in humans and other animals”.

Pet owners beware — don’t let your dogs lick any toads.

“Eye” wonder

Last year I wrote about the possible basis for the many variations of eye color in birds (click here to read that post).  Unlike most mammals which sport a limited variety of pale blue, gray, green, to dark brown shades, I’ve noticed that frogs and toads, like birds, also exhibit a rich variety of eye colors.  And so, “eye” wonder why?

LEOPARD FROG-

Leopard frogs have a golden-colored iris with some dark speckles running through it.

GRAY TREE FROG-

Similarly, Gray Treefrogs also exhibit that golden-colored iris with the darks streaks running through it.

But these highly colorful eyes are tame, compared to those of a couple of South American frogs.

ghost glass frog

Those are some mesmerizing eyeballs in this Ghost Glass Frog. Glass frogs have see-through skin, especially on their ventral surface, which is as transparent as glass permitting a view of their internal organs.  Are those wild purple lines etched on the silver background of its iris to captivate female glass frogs, or frighten potential predators?

Red_eyed_tree_frog_

Red-eyed Treefrogs sit quietly on the underside of leaves during the day. But if disturbed by a predator or nosy human, they flash their big red eyes, orange toes, and yellow and purple legs to startle and gain time to escape.  [Photo from Wikipedia, By Carey James Balboa via Wikimedia Commons]

The variety of eye color in frogs and toads is astounding, as captured in this collage by Jodi Rowley.

eye color in frogs-Jodi Rowley

Just a sampling of the normal variation among amphibian species… From RealScientists.org

Surely all this ocular advertisement has purpose — beyond frightening would-be predators?  Any speculation from you, dear readers?

In addition to the flash of color provided by the wide-open frog eye, you may have noticed that frogs have the ability to project their eyes outward from their head, or retract the eyes inward level with their skull.

leopard-frog-swimming

This leopard frog has staked out a calling site, hoping to attract females. But it’s broad daylight and he needs to be able to see approaching predators (and photographers). 

Extrinsic eye muscles that elevate the eye above the level of the head actually give the frog a 360 degree view of its environment.  Movement of the eyes downward presses on the roof of the frog’s mouth, helping to propel food down the back of the throat toward the stomach.  Eyes — the multiple use organ!

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.

Frogs!

Off and on rainy days with warm(er) temperatures have really set the frogs in motion here.  I sat on an upended bucket by one of the ponds in the backyard and trained my binoculars on the pond’s edge, hoping to finally locate those tiny little creatures that were making that hugely loud racket.

Eventually, by trying to ignore the loudest chirpers, I could distinguish three different types of calls, all at different pitches, frequencies, and volume.  Finally, by staring at the water where I thought the calls were coming from (this takes sound localization ability, which apparently I am lousy at), I found the frogs making them.

Leopard frogs made very low intensity calls, very infrequently, and I couldn't really see where the sound was coming from (no obviously inflated pouches).

Leopard frogs made very low intensity, low pitch calls, and call very infrequently.  I couldn’t really see where the sound was coming from (no obviously inflated pouches).

Wood frogs sit horizontally in the water Ilike the leopard frogs, emitting sort of a quacking call that sounds like it should be coming from a duck.

Wood frogs sit horizontally in the water, like the leopard frogs, emitting sort of a quacking call that sounds like it should be coming from a duck.  Dark bodies, striped legs, and a black mask over the eyes outlined with white stripes — make this frog quite attractive.

wood frog, Rana sylvatica

Here the wood frog has inflated its vocal sacs during its "quack" call.

Here the wood frog has inflated its vocal sacs during its “quack” call.  When they do this, the water around them shows disturbances in concentric circles, making them a little easier to find in the pond (if you have bad sound localization ability).

Wood frogs are found almost everywhere in central and eastern North America; they are one of the first frogs out in the spring, as soon as the ice melts off the ponds.  They are unique in that they tolerate being frozen solid over the winter, as they “hibernate” in a state of suspended metabolism under the leaf litter.  Click here to view a short video of wood frogs calling (in Minnesota).  And here is an amazing video of Wood Frogs defrosting from their frozen winter state.

By far, the loudest, shrillest, and almost deafening calls were coming from the Boreal Chorus Frogs (Pseudacris maculata), which were almost impossible to find, mostly because I was looking in the wrong places.  They were sitting at least 3 feet from the shore, out in the submerged vegetation, oriented vertically, with their head, vocal sacs and abdomen out of the water.  Perhaps the volume of noise from multiple frogs confuses predators as well.  Are herons and egrets immune to this racket?

Even maximum telephoto didn't bring these tiny, one-inch Chorus frogs into view.

Even maximum telephoto didn’t bring these tiny, one-inch Chorus frogs into view.  

So, I moved to a better viewing spot, sat, and waited until they got used to my presence, and then got closer-up views of a calling Chorus Frog.  These frogs (once you see them) are easily distinguished by the three longitudinal stripes down their backs.

The cricket-like call is emitted through the larynx (voice box), but is amplified by vocal sacs.  The body cavity of the frog swells when air is inhaled through the nostrils, and the vocal sac shrinks.

The cricket-like call is emitted through the larynx (voice box), but is amplified by vocal sacs. The body cavity of the frog swells when air is inhaled through the nostrils, and the vocal sac shrinks.

Then, the frog contracts its muscles to expel the air during exhalation through the larynx, enlarging the vocal sac, and producing a vibration that amplifies the sound.

Then, the frog contracts its muscles to expel the air during exhalation through the larynx, enlarging the vocal sac, and producing a vibration that amplifies the sound.

If you haven’t had the pleasure of standing next to a group of calling Chorus Frogs, you can view a short video here.  These tiny frogs can emit sound at nearly 90 decibels, which is about as loud as the human ear can stand without damage, about the same as standing next to a truck without a muffler.  And, they call continuously for hours and days on end.  Now how is that for amazing!

For good photos and descriptions of MN frogs and toads, you can click here.

Why are frogs green?

I happened to notice blue speckles on the face of the frog in the last post and thought it might be an aberration of the image capture.

But it’s not — it’s due to the chromatophores in the frog’s skin. It’s the answer to why frogs are green, or blue, or red and orange, or how they change color from one shade or pattern to another.

The pattern of color in this subadult Gray Tree Frog (also inhabiting the rain barrel along with the adult in yesterday’s post) shows the range of colors in this species — from almost white to dark green.

If you zoom in, you see patches of skin that are white, various shades of gray, and a range of shades of green almost to black. On the right side of the photo are patches of skin reflecting blue-green instead of green, which suggests the use of structure to produce color (as discussed earlier in birds).

It turns out that 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.

Frogs that lack xanthophores are various shades of blue, like this blue poison dart frog found in Brazil. Black spots are created by the melanophores underlying the iridophores.

(photo from Wikipedia)

So the answer to why frogs are green comes from the interaction of the chromatophores in the top two layers — iridiphores that produce blue color and xanthophores that produce yellow color. As any school kid knows, mixing yellow plus blue yields…

(photo by co-blogger Alison)

And, more amazing is the fact that Gray Tree Frogs can change color to suit their background (or their mood) within seconds, not as fast as a chameleon, but fast enough. They do this by dispersing (darker color) or contracting (lighter color) the pigment granules within the chromatophores or even changing the entire shape of the cell.

Frogs in a barrel

Where did that expression “like shooting fish in a barrel” come from?  Meaning it’s so easy, you can’t miss?  Well, you can’t really miss when you take photos of tree frogs in a rain barrel either, except when you have absolutely no room to get behind the camera viewer and have to hold it over your head and point randomly downward hoping the subject is in the photo, like this.

Gray Tree Frogs hang around landscaped dwellings in the summer after they breed in the nearest pond.  They especially like outdoor lights…and rain barrels, where they find lots of tasty insects to eat.  They climb vertical surfaces with ease using those super-sticky toe pads.

(Photo from Hanna and Barnes, 1991, Journal of Experimental Biology 155: 109)

However, there is no glue or adhesive secreted, just the simple physics of the surface tension developed by a large area of moist skin pressed against a flat surface.  It’s the same principle used for suction cups that stick to vertical glass surfaces.  For greater sticking power, frogs press their belly and thigh skin against the surface as well, and can stay put at angles of as much as 150 degrees from horizontal (i.e., tending towards upside down).  Read more about how this was determined here.

(Photo by co-blogger Alison)

Early morning visitor

I was filling the rain barrel we use to automatically water the potted plants and found a visitor sampling the fresh water.  When the frog saw me, it dropped to the bottom of the 50 gallon tank, but eventually made his way up to the top again and allowed me to take its photo before departing.

The yellow coloration inside the hind limbs and the slightly warty skin, along with the rounded disk-like suckers at the tips of the toes make this a Gray Tree Frog (Hyla versicolor).  It can change color (slowly) from gray to green, which is why they are not Green Tree Frogs.  They are found all over eastern North America in deciduous forests, and are usually active at night up in the trees, although they do descend from the trees to breed.  Perhaps this was a female, checking out my rain barrel as a potential egg laying site.

This is somewhat of an unusual frog because it has double the number of chromosomes of its close cousin, Cope’s Gray Tree Frog (a southern species).  Usually doubling of genetic material is a bad thing, but apparently not for this species.

Prairie Spring

We took a field trip to Glacial Lakes State Park this weekend to take photos of the prairie wildflowers.  Hah!  Wildflowers are not fooled by a little warm weather in March.  They can monitor the daylength and “know” that the real spring weather (and rain) comes in April and May.  We unfortunately picked a rainy cold weekend to survey the prairie, but there were a few interesting highlights to see.  Just to give you an idea of the obstacles to our viewing pleasure, there was fog…

and a steady drizzle during one of our hikes (photo by Alison) …

with clouds threatening to pour down on us a lot of the time (photo by Alison).

The wildflowers made bright spots of color in the mat of taller grasses, like this Hoary Puccoon, which is almost orange  (photo by Alison).

Prairie Smoke is so-named for the structure formed by the maturing seed.  The flowers are a pretty magenta color but droop down, while the seed head will later be an erect wispy fringe on the flower stalk, resembling a plume of smoke.

Prairie Plum has low clumps of purple pea-like flowers that will later form an inflated orange-red pod lying close to the ground.  Apparently the pods taste much like fresh peas, which is logical since it is a pea family plant.

Another early bloomer is Golden Alexander, with its taller and erect flattened panicles of yellow flowers. 

Scattered throughout a wet, marshy field, we found Jack-in-the-Pulpit already well into its blooming phase.  The seed head of the central spike (Jack) will form a bright red cone of berries in the fall.  (see The Worm, the Pulpit, and the Thorn Plant, Nov. 29, 2011)

Even though it was rainy and misty most of the time, the were lots of birds out singing and flying around.  As we drove the backroads around the glacial lakes we saw a couple of Trumpeter Swans… (photo by Alison)

a small group of White Pelicans on Lake Minnewaska, (photo by Alison)

and the grandkids found a frog on the trail — it was very lethargic, either from the cold or having been injured earlier.

(photo by co-blogger Alison Mickelson)

As eldest grandson summed up at the end of our wet hike, “sometimes you find unexpected treasures in pretty boring places.”