Vert-de-Gris

Cope’s gray treefrog on a pepper plant. Photo: Alan Howell © 2017, Star Path Images, Used with Permission.

It isn’t easy being green. Kermit the Frog said it, so you know it has to be true.

He’s always seemed a reluctant celebrity, so my guess is that being the most famous Muppet-amphibian on the planet isn’t always a picnic. I wonder whether life would be a little less stressful if, like some of his cousins, Kermit could change from green to another color when he’d rather not be so conspicuous.

North American gray treefrogs know how to be seen and when to blend into their surrounding, shifting the spectrum from bright emerald to peridot, to gold, copper, platinum, silver, and even gunmetal. Since the places they hang out — trees and shrubs in woodlands, meadows, prairies, swamps, suburbs, and cities — tend toward palettes awash with green and gray hues, these arboreal amphibians can keep their sartorial choices simple. 

What looks like a costume change is actually a rather high-tech, cellular-level special effect created by chromatophores. These pigment-containing and light-reflecting cells, or groups of cells, are present in the skin of certain frogs, as well as some reptiles (including chameleons), cephalopods (such as octopi), fish, and crustaceans. Mammals and birds, on the other hand, have melanocytes, a different class of cells for coloration.

Chromatophores are classified based on their hue under white light:

  • melanophores (black/brown)
  • cyanophores (blue)
  • erythrophores (red)
  • xanthophores (yellow)
  • leucophores (white)
  • iridophores (reflective or iridescent)

The process, known as physiological color change, can be controlled by hormones, neurons, or both. Most studies have focused primarily on melanophores because they are the darkest and, therefore, the most visible. When pigment inside the chromatophores disperses throughout cell the skin appears to darken; when pigment aggregates in cells the skin appears to lighten. Either way, you’ve got an amazing makeover, or a convincing disguise, in no time flat! 

There’s even more to the gray treefrog’s ability to assume an alter-ego than meets the eye —what appears to be a single species is actually two very close relatives: Hyla versicolor, aka Eastern, although there’s a long list of pseudonyms from which to choose (there are more ways to hide than blending into the substrate); and Hyla chrysoscelis, aka Cope’s (which also has a couple of nicknames but not as many as H. versicolor).

Cope’s and Eastern are equally skilled at clinging to and climbing slick surfaces using large toe pads that secrete mucous, creating surface tension. It’s not uncommon to find one plastered against a window pane (allowing for an interesting view of their nether-regions). Both species prefer a diet of small insects, spiders, and snails. Both hibernate under leaves, bark, or rocks. Well, “hibernate” sounds a lot more cozy than the reality… which is that their bodies pretty much freeze and their lungs, heart, brain, and other organs stop working until they thaw out and reanimate in the spring. It’s a pretty nifty chemical trick, on par with being able to transform your complexion at will. 

Kermit has an unmistakable personal brand, but distinguishing H. versicolor from H. chrysocelis visually is just about impossible. Both Eastern and Cope’s are relatively small (1.5—2.0 in/3.5—5 cm), and the adults are often mistaken for younglings. Both wear a sweep of bright citrus-orange along the inseam of their hind legs (a signature shade is all the rage, you know).  Females of both species are usually (but not always) larger, with a ladylike white throat. During the breeding season, males have a macho (make that hipster, since it resembles a beard) black, gray, or brown throat. Guys sing. Gals swoon, but don’t sing along.

The ranges of these two species overlap, but Cope’s are more widely distributed. If you find a gray treefrog in North Carolina or Georgia, you can be reasonably certain it’s a Cope’s, but if you’re in Iowa or Pennsylvania, all bets are off. The only risk-free way to know for sure is to do a DNA test — Cope’s are a diploid species, meaning they have two sets of chromosomes, one from each parent (for a total of 24); Easterns are a tetraploid species, meaning they have four sets of chromosomes (for a total of 48).

Now, some frog call connoisseurs claim they can detect variations in breeding calls, and that Cope’s treefrogs have a faster and slightly higher-pitched trill than Easterns. But the call rates of both species change with ambient temperature… so color me skeptical.

[Postscript:  What kind of frog is Kermit? While I’ve never found a definitive answer to this question, I always assumed that because he was created/discovered by Jim Henson, he was probably Hyla muppetalis or Rana hensonii… something like that. However, in 2015 Brian Kubicki of the Costa Rican Amphibian Research Center discovered a frog who, if not the same species, must at least be a first cousin, or possibly Kermit’s doppleganger.]

Diane’s bare-hearted glass frog (Hyalinobatrachium dianae). Photo: © Brian Kubicki, Costa Rican Amphibian Research Center, Used with Permission

[Thanks to the photographers who granted permission to use their photos, and to those who made their work available through the Creative Commons license: Dave Huth(composite of color variations), , Chiswick Chap & CheChe, (melanophores schematic), Alan Wolf, Andrew Hoffman, and Douglas Mills© 2017 Next-Door Nature. Reprints welcomed with written permission from the author.]

Virtuosity

Maybe Bobby McFerrin was a house wren (Troglodytes aedon) in a previous life.

This thought popped into my mind when, after listening to On Being’s Krista Tippett interview the singer, I went out for a walk with my canine companion. We hadn’t made it too far down the sunny trail when we were suddenly drenched by a deluge of liquid notes. That vocal tsunami, pouring forth from an entirely disproportional feathered Dixie cup, stopped me in my tracks.

Like McFerrin, who is known for fluid, polyphonic singing and quick, oceanic octave jumps, the wren’s song bounced around like raindrops on pavement. I suppose that’s why the synapses in my brain connected the two muscians.

There are definite differences between these gifted songbirds, though.

For example, wrens and other passerine birds produce vocal sounds using an organ called the syrinx, positioned where the trachea splits into two bronchial tubes. Each side of the syrinx operates independently, so songbirds can produce a sweeping range of notes in fractions of a second, or two different pitches at the same time, or simultaneous rising and falling notes, all without stopping for a breath. Humans, by contrast, make vocal sounds by sending air from the lung into the windpipe, through folds (aka vocal cords) in the larynx, and out to the throat, nose, and mouth.

Admittedly, McFerrin often sounds as if he has a syrinx but, hard as it is to believe, he’s making all of those notes with the same equipment you and I have. It’s just that he’s playing every instrument in the orchestra, and we’re barely pecking out “Chopsticks.” His ability to switch pitch is inarguably stunning; however, even this virtuoso can’t match the speed of a wren running through the scales.

McFerrin has a rich and ever-expanding repertoire that includes pop, a capella, choralclassical, spirituals, and movie scores. Like any jazz artist worthy of the title, he is a master of improvisation; always learning, always expanding his technique, consistently creative and ready to try something new. Wrens, on the other hand, may sound like they’re jamming but they’re actually shuffling 12-16 stock syllables… kind of like a classically trained musician who learned to play according to the rules of the conservatory but wants to sound cool enough to swing.

You see, passerines begin their musical education when they are barely out of the egg, during a development phase known as the critical period. Listening to the adult birds around them, the youngsters tune in to the songs and calls of their own species. Once young wrens have left the nest they practice, over and over and over, dialing in the sounds until the song matches the memory. With the exception of mimicking species (e.g., mockingbirds, catbirds, and thrashers), there will be no extemporization. That’s because wrens choose a mate based on the ability to cover “their song” note for note. Some bird songs have geographic variations, sort of like regional accents, but chicks want a boy who sounds like he’s from the neighborhood, and will pass over anyone who sounds too exotic or experimental.

I’m much less discriminating, at least on that score. Bubbling, effervescent singing, whether it’s an improv by McFerrin or a house wren standard, always helps me tune out my worries… and that makes me happy.

[Play both videos at once so Bobby and the house wren can duet!]

 

[Thanks to the following photographers for making their work available through the Creative Commons license: Dustin Gaffke, , Todd Van Hoosear, and Rachid H.  © 2017 Next-Door Nature. Reprints welcomed with written permission from the author.]

Shell Game

eastern box turgle

Eastern box turtle shells provide protection from predators, but not the hazards of life in cities and suburbs (Photo: Alan Howell © 2010 Star Path Images, used with permission)

[This post is a reprint from 2011, prompted by Dash’s discovery of a box turtle on our evening walk last night–enjoy!]

Sometimes you just need to shut out the world for a while, you know?

Maybe you can’t relate but I know the eastern box turtle (Terrapene carolina carolina) certainly can. Whether the threat is carnivores or the impending return of students to campus, there are times when nothing beats a little self-imposed solitary confinement.

Carrying a personal isolation chamber on your back means sensory deprivation can be achieved in mere seconds. No need to call ahead for an appointment at the local day spa. Don’t bother dimming the lights, closing the blinds, and turning off your cell phone. Just pull in your extremities and slam your hinged shell shut—a little privacy, if you don’t mind!

eastern box turtles

Hello… goodbye!

Is it any coincidence that box turtles are one of our longest-lived species, with well-documented cases of individuals who reached and then passed the half-century mark? Stress reductions, in the form of a room of one’s own, may well be the key to attaining a ripe old age.

We shouldn’t dismiss the importance of wise food choices either—lots of lean protein, in the form of earthworms, snails, slugs, and insects, as well as fruits and veggies such as berries, grasses, and flowers.  Turtles have another favorite food that may contribute to overall longevity—they’ve been known to consume poisonous fungi, causing anyone who dines on that particular portion of turtle meat to sicken, or worse.

Of course, someone has to kill and eat said turtle before suffering the consequences, which may not seem like much of a survival benefit unless you consider it from the standpoint of the population, rather than the individual. See, all it takes is one or two bad dinners and, ever after, box turtles become a much less appealing meal for that particular consumer. The technical term is adverse conditioning—that’s a polite way of saying animals (both human and non-human) tend to stop eating things that make us vomit.

Now, it’s unlikely that turtles have that particular life-extending strategy in mind when eating wild mushrooms, but other kinds of magical fungi have been credited with providing a variety of benefits, including an improved sense of well-being and decreased anxiety levels. Perhaps box turtles are self-medicating with the Terrapene equivalent of Xanax®.

One of six subspecies of the common box turtle (T. carolina), the eastern, like all its kin, has a highly domed carapace (the upper portion of the shell) and a hinged plastron (the lower half of the shell). What sets each subspecies apart is distribution and habitat, as well as certain physical characteristics.  T.c. carolina, found from southern Maine to southern Florida and as far west as central Texas, is known for a colorful keeled carpace that features diverse combinations of spots, bars, and radiating lines.

Color provides a clue to more than a box turtle’s species. It can also help us determine the gender of that lurching, resolute reptile we stop to help cross the street.  If the eyes (irises) are bright orange or red, you’re holding a male; females have brown or light orange eyes. What if, in response to your good deed, the turtle has gone into hiding, making eye contact a moot point? Simply turn the creature over; females have a flat plastron, males are slightly concave. (You know… birds do it, bees do it…).

The hinged plastron is what caused taxonomists to create a separate genus for North America’s box-top reptiles, and what allows the eastern and it’s relatives to retreat into a kind of biological fortress. For most of their history, this survival strategy worked quite well against predators like coyotes, raccoons, and skunks.  Sadly, it doesn’t provide the same level of protection from every threat.

Box turtles are still relatively common throughout much of their range, but not even the most tightly closed shell can shield this species from the impacts of habitat loss and interactions with Homo sapiens. These are slow moving, slow growing creatures with delayed sexual maturity and low reproduction rates, all of which puts them at risk. A female may produce hundreds of eggs during her lifetime, but less than a dozen offspring can be expected to survive to adulthood.

It’s hard to even begin to estimate how many turtles are hit attempting to cross roads every year, and there are plenty of other hazard against which withdrawing into your shell is of little use—trains, lawn mowers, tractors, and bulldozers, to name but a few. Then there’s the capture of turtles for the pet trade. In many states, this practice is completely unregulated, with devastating impacts on wild populations.

Even so, there are still times when coming out of your shell is the better choice. Especially for humans. Solitary confinement is used as a punishment because, unlike turtles we are social mammals. We need companionship, conversation, touch. Hard to get any of those needs met when you retreat to your shell. Unless, of course, you invite someone to join you there.

[Thanks to the following photographers for making their work available through the Creative Commons license: Doug Letterman, Bill Lynch, Shane Kemp, Brian Hefele, and  Chesapeake Bay Program.  © 2011 Next-Door Nature. Reprints welcomed with written permission from the author.]

Track & Field

cottontail leaping

Back to school, and to early morning practice before class – hop to it!

[Students are returning to my university town for the start of another academic year… so in honor of college athletics I’m offering a slightly-edited instant replay of this post about cottontail rabbits that originally ran back in April 2011.]

On your mark…. Get set… HOP!

An article I read while eating breakfast had me thinking about track meets as the terrier-boy and I set off for our morning walk.  That piece may be why I noticed, for the first time, how runners imitate the posture of a rabbit as they settle into their starting blocks. Human runners have to fold themselves up to gain the potential energy advantage of a crouching leg, but rabbits are always ready for the starting gun.

sprinters

In 2009, Usain Bolt set a record of just over 23 mph in both the 100- and 200-meter, but he’s an exception even among world-class athletes. It’s nothing out of the ordinary for Sylvilagus floridanus to reach speeds of 18 mph, and they can maintain that speed for close to 800 meters… while zig-zagging to change direction every few strides. Let’s see Bolt try that!

racing cottontailsMost sprinters are specialists, but cottontails and other Lagomorphs, with the exception of pikas (Ochotona princeps), also excel at hurdles, steeplechase, and in some field events. Okay, they can’t throw a javelin or a shot-put, but they leap to the top of the score board when it comes to jumping.

leaping cottontails

Longing to see a long jump? At first glance, a cottontail’s 4.8 m (15 ft) may not sound too impressive when compared to current world record holder Mike Powell’s 8.95 m (29.4 ft), set in 1991. But consider this: a 4.8 m leap is 10x the average length of an adult cottontail’s body; 9 m is barely 5x the average height of an adult American male.

How high can they flycottontail courtship? The men’s high jump record stands at 2.45 m (8 ft), set in 1993 by Javier Sotomayor of Cuba. That’s only 1.4x the average height of Olympic jumpers. While courting, both buck (male) and doe (female) cottontails will jump 0.6 m (2 ft), nearly twice their height, to demonstrate worthiness. By that standard, not even elite human athletes would be able to find a mate.

cottontail courtship 2Once the mating ritual (which also includes a little boxing, just to keep things interesting) is complete, 1-12 kits are born approximately 28 days later. A doe will often mate again within hours of giving birth—what a woman! Admittedly, she’ll only visit the nursery when it’s time to feed the kids so she’s not going to win any “most attentive mother” awards. But, to be fair, compared to her baby-daddy she’s a doting parent, and staying away keeps predators from getting wise to the location of the nest. It will take her 3 weeks to wean one set of youngsters, then she’s got about 1 week to recuperate before the stork arrives again.

Still not impressed? She may have up to 7 litters in a single year.  Now, I call that a marathon.

[Thanks to the following photographers for making their work available through the Creative Commons license: Porsupah ReeRob Helfman, and Michale Connell.  © 2011 Next-Door Nature. Reprints welcomed with written permission from the author.]