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.]

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.]

Lonesome Doves

It’s a fine world, though rich in hardships at times. ~ Larry McMurtry

There’s a sweetness in the lament of a mourning dove (Zenaida macroura) that makes the sorrow bearable, and believable. Theirs isn’t an pop tune about a hookup with a hook, or a power ballad tale of infatuation, thrill, and transitory heartbreak. When mourning doves call I hear a country-western melody about spacious, isolated landscapes and complicated lives composed of joy and calamity, love and betrayal, not to mention good and evil that can’t be easily differentiated by the color of someone’s hat.

Country music has had it’s share of singers who could wail with convincing anguish on stage, then party ’til the cows came home once the show was over… so I have to wonder if the mourning dove’s high lonesome yodel —coo-OO, COO, coo — is simply part of the act. After all, that grievous angel cry is replaced by a jaunty whistle of wings every time they launch skyward.

Plus, doves are rarely alone and don’t seem to have much time in their lives to feel lonely. The whole clan is known to grow up fast (reaching sexual maturity at about 85 days old) and then pair up into monogamous ’til-death-do-we-part couples who take the directive to be fruitful and multiply seriously… as in up to twelve chicks in a single season serious (six broods of two chicks each). Both Mom and Dad are doting, active parents who share grocery shopping and child care equally, rarely leaving their babes unsupervised by at least one adult at all times.

The end of the lovey-dovey breeding season shouldn’t bring on the lonesome blues either, because that’s when the community flocks together in a big way. They go on group picnics, gobbling up seed in open fields or from the ground beneath backyard feeders until their crops are full, then settle onto fences, or walls, or telephone wires to digest the meal and the days events. They go drinking together, although for doves that means sipping water from puddles and bird baths rather than throwing back with Jose Quervo at the neighborhood saloon.

The community even sleeps together— literally, not euphemistically — roosting in trees and other protected areas. Comforted by the safety of numbers, they’ll drop their heads comfortably between raised shoulders rather than tucking in beneath a wing or over the back as so many other birds do.

Despite all the social network support, there is a darker side to the life of a mourning dove that may explain their doleful song — they often end up on the wrong end of a gun. Mourning doves are abundant, with a population estimated to be comprised of nearly 500 million individuals, but they are classified as a game bird and are the most frequently hunted species in North America. As many as 70 million are shot by hunters each year. Those who dodge the bullet still have to contend with the threat of lead poisoning from shot picked up from the ground while feeding.

Despite what their name implies, though, when one of these doves becomes a widow or widower they don’t spend a lot of time in Brokenheartsville bemoaning their newly-single status. In fact, they pair up again pdq. After all, ya can’t be fruitful all by your lonesome.

 

[Thanks to the following photographers for making their work available through the Creative Commons license: Sarah Richter, Chuck Roberts, George Thomas, Tina :0), Edward Peters, and Patty Myrick.  © 2017 Next-Door Nature. Reprints welcomed with written permission from the author.]