Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
Stephen Knight spotted an iguana when checking into his hotel in Tulum, Mexico. I put up the quiz earlier, and now here’s the reveal. Did you find it?
This appears to be a black spiny-tailed iguana, or Ctenosaura similis. Readers can correct me if I’m wrong, as it may be a green iguana.
We have a melange of photos today, but will start with Stephen Barnard’s documentation of the eaglets growing in Idaho:
Lucy (?) and a fast-growing chick:
The nestlings are exercising their wings.
Nearby lives a Great Horned Owl (Bubo virginianus):
Anne-Marie Cournoyer found what appears to be a mating aggregation of garter snakes (Thamnophis sirtalis) in the Parc du Mont-St-Bruno outside Montreal:
And nearby, a miracle!!! Explain this if you can:
Black-capped chickadee (Poecile atricapillus). The Cornell bird site notes that it is “a bird almost universally considered ‘cute’ thanks to its oversized round head, tiny body, and curiosity about everything, including humans.”
Mourning dove (Zenaida macroura):
And finally, a space photo by reader Don McCrady:
Here is an image of M101, also known as the Northern Pinwheel Galaxy, which forms a neat triangle with the last two stars in the handle of the Big Dipper. It is a large face-on spiral galaxy that lies about 20 million light years away. Its grand spiral shape is deformed by the gravitational attraction of other galaxies in its vicinity, including the dwarf galaxy NGC 5477 seen near the left edge of the image. As you can see, the galaxy is literally dotted with bright active nebular regions called HII regions, brought out in this image with the addition of 2 hours of separate Hydrogen-alpha exposures. Seven of these bright knots actually have their own designations in the New General Catalog (NGC).
Total exposure time for this image was over 7 hours, with over 2 hours of luminance, 3 hours of RGB colour data, plus 2 hours of Hydrogen-alpha. The image was captured through a Stellarvue SVS130 f/5 apochromatic refractor and a SBIG STL4020M camera, taken from my backyard in Redmond, WA. The final image was upsampled 2x.
Reader Karen Bartelt photographed nature red in beak and claw:
Coopers hawk (Accipiter cooperii) dining on northern flicker (Colaptes auratus) in my driveway. Full service birdfeeding.
Reader Stephen Barnard offers this as an example of mutualism:
A couple of Black-billed Magpies (Pica hudsonia) picking parasites (I assume) off a bull moose (Alces alces).
And a reptile from Richard Dahl of South Dakota:
Here’s a bullsnake (Pituophis catenifer sayi) photo from Devil’s Gulch near Garretson, South Dakota. Devil’s Gulch is a site of a Jesse James / law enforcement shootout, now turned into a place for a picnic and a quick hike. The snake was right by a walkway to get to the other side of the gulch. It was not happy about having visitors, and put on its best rattlesnake impression. Gave me a nice startle.
Bullsnakes are sometimes mistaken for rattlesnakes and killed. Owing to its coloration, dorsal pattern, and semi-keeled scalation, the bullsnake superficially resembles the western diamondback rattler (Crotalus atrox), which is also common within the same range. The bullsnake capitalizes on this similarity by performing an impressive rattlesnake impression when threatened. First, it hisses, or forcibly exhales through a glottis or extension of the windpipe. The end of the glottis is covered by a piece of cartilage known as the epiglottis which flaps back and forth when air is exhaled from the right lung producing a convincing rattling sound. It also adopts a rattlesnake-like “S-curve” body posture as though about to strike. It will commonly vibrate its tail rapidly in brush or leaves, and flatten its head to resemble the characteristic triangular shape of the rattlesnake. These defensive behaviors are meant to scare away threats, however, and not to sound an attack.
by Greg Mayer
Last month I took a trip, and posted a “spot the _____” post for an animal I’d seen and photographed, but without giving any geographic location clues, so as to make identification more challenging. Despite this, many readers were not only able to spot it (not very hard), but also identify it: a cottonmouth. It is, more specifically a western cottonmouth (Agkistrodon piscivorus leucostoma), and I photographed it in the Cache River State Natural Area in southern Illinois. Here she is again, in a slightly different view. You can see she’s right in the middle of the footpath, and blends in fairly well with her background. By the time this photo was taken, she was pretty agitated and had reared up, so she stood out more.
Southern Illinois is very interesting from a natural history point of view, both geologically and biologically. The southern part of the state narrows to a point where the Mississippi and Ohio rivers join. A bit north of their confluence you find a set of hills crossing the state from west to east, called the Shawnee Hills or “Illinois Ozarks“. Illinois is otherwise exceedingly flat (in Wisconsin, Illinoians are know as “flatlanders”, and considering how flat Wisconsin is, that’s saying something), so the Hills are a distinctive landscape feature. Composed of Carboniferous sandstones and limestones from the mid-Paleozoic epicontinental sea that covered what is now the middle of the U.S., differential erosion has created many interesting land forms, including Camel Rock and Giant City.
Biologically, many southern species reach the northern limit of their range in southern Illinois. (Culturally, too– having driven several times from Chicago to the Gulf coast in Mississippi, I can attest that you enter the Bible Belt somewhere in southern Illinois, and leave it about ten miles north of the Gulf of Mexico.) In the Hills you get a high diversity of oaks (my favorite trees), but just south of the Hills you enter the flat Cache River country full of cypress and tupelo swamps, two species at the northernmost edge of their ranges. The Cache River itself is a remnant of an old bed of the Ohio River.
The giant old cypress above is said to be 1000 years old, with a basal circumference of 43 feet (13 m). A couple of buttresses from a second very large cypress can be seen at the right; that tree is known as the “Winnie the Pooh Tree“. Cypresses are known for having upward projections from their roots that stick above the water, known as “knees”; their function is unclear.
My wife and I spent one day hiking in these swampy areas in a few different places, and were well rewarded by our hike along the edge of Little Black Slough, a tupelo/cypress swamp.
We saw and photographed a bald eagle– it looked much better through binoculars!
After 3 days of hiking, our herpetological findings had been limited, just a few true frogs and painted turtles. Southern Illinois is the northern edge of the range for cottonmouths and copperheads, but I had begun to think the season was not far enough advanced to have a chance to see them. At 3:30 in the afternoon, when basking was likely to be done for the day even if the snakes were active, I thought our snake chances were over.
Just moments after the photograph above was taken, the photograph below was taken. My wife had stepped over or next to the snake. A pace behind her, I saw it—a thick bodied, banded snake, right next to the water—and I immediately thought “water snake or cottonmouth?” I changed my step in mid-stride, awkwardly hopping over the snake and turning to face it– no doubt, it was a cottonmouth!
It too had turned to face me, and raised and pulled back its head, opening its mouth and exposing its “cotton” mouth. In the picture below, you can see several neat feature of the snake’s biology. First, is the aforementioned open-mouthed threat display, enhanced by the mouth color. Second, note the eye, divided into dark and light halves, that break up its identifiable shape, helping to camouflage the snake. Between the eye and the lip, note the white pit, which is an infrared sensitive structure which enables the snake to get a “thermal picture” of its environment, and the thing from which “pit vipers” get their name. Pit vipers can strike a warm object accurately using only their pits to locate the object. And finally, the fangs are in the long folds of the buccal mucosa alongside the lips on each side of the mouth. The fangs can pivot, and would swing forward out of the surrounding tissue when the snake actually tried to bite, either for predation or defense. (Click on these photos to enlarge them and see more details.)
I took these pictures with a Nikon camera I had gotten for Christmas, and was pleased to find you could actually see the blood vessels in the snake’s mouth, but I was too unfamiliar with it yet to figure out in the moment how to take video. So, my wife used her cell phone.
Note the vigorous “rattling” of the tail– many snakes do this, not just rattlesnakes. Against the substrate and dry leaves, this can be quite noisy, and in a cottonmouth acts as another threat beyond the white, open mouth display. Rattlesnakes have taken this further, with the loose fitting, keratinous, rattle scales at the tip of the tail capable of making a loud buzzing sound. In the video I mention the “quite long” tail to note the smooth tapering of the tail from the cloaca, indicating this is a female. Having said that, I immediately realized that to most people it would seem that the tail is shorter than they expected, so I then say it is a “fairly short” tail. The two statements are not contradictory– just pointing out different aspects of the snake’s tail: the tail shape showing its sex, but also that, as in most snakes, the tail is relatively short compared to the body length.
A natural history tour of this area of Illinois is well worthwhile, with many state and federal protected lands. The one criticism I would make is that in most areas the interpretive materials (i.e. signage) are sparse to lacking. There is, however, a fine, small museum run by the state of Illinois, the Barkhausen Cache River Wetlands Center, and I would recommend beginning a hiking tour with a couple or more hours there first.
Greene, H.W. 1997. Snakes: The Evolution of Mystery in Nature. University of California Press, Berkeley. (excellent general natural history of snakes that we’ve had occasion to recommend here before)
Smith, P.H. 1961. The amphibians and reptiles of Illinois. Illinois Natural History Survey Bulletin 28:1-298. (details on Illinois herpetofauna)
by Greg Mayer
Following up on Matthew’s linguistic investigation of larval amphibians, I’d like to address another amphibian linguistic conundrum: the English words for adult members of the order Anura. Just as we have two standard words for a larval anuran in English, we have two standard words for the adults: frog and toad. But this linguistic duality comes nowhere near encompassing the biodiversity of anurans. There are, by many estimates, over 40 families of anurans. I myself consider this taxonomy a bit oversplit, but even a conservative taxonomy would have more than two dozen families. There are thus many more sorts of anurans than there are English words to name them. Why is this so?
The answer, I believe, is simple. In Great Britain, where the language developed, there are four native species: two frogs (Rana temporaria and Rana lessonae), and two toads (Bufo bufo and Bufo calamita). So in England, there are indeed only two sorts of anurans. Here’s one of the frogs, the common frog (North American readers will note the resemblance to our wood frog, Rana sylvatica, which also has a tympanic dark spot and dorsolateral folds):
And here’s one of the toads, the common toad (the green flecks are duckweed or some other plant):
We can distinguish frogs from toads, because frogs are more aquatic, with long hind limbs for jumping, webbed toes (easily seen above), and moist, smoother skin. Toads are more terrestrial, squat with short legs for hopping, and have dry, warty skin. And this distinction works for the anurans of Britain– the frogs are members of the family of “true frogs”– Ranidae, while the toads are members of the family of “true toads”– Bufonidae.
As the English encountered more kinds of anurans around the world, each new anuran was shoe-horned into being either a frog or a toad. Thus the long limbed, arboreal, jumping anurans of the family Hylidae (which English nobility would have encountered in their Continental estates) were called, aptly enough, tree frogs. And in the North American colonies, the squat, warty burrowing members of the family Pelobatidae were called spadefoot toads. But with dozens of families of anurans, and a great diversity of ecological habits and body forms, the distinction breaks down, and our English common names wind up forcing an exuberant diversity into just two names.
I wonder to what extent the biodiversity of a language’s native land influences the language’s naming diversity. In the only other language I (sort of) speak, Spanish, I know three words– rana (for frogs), sapo (for toads), and maco. The latter is a word I learned in the Dominican Republic, and it has a very different meaning in standard Castilian, as given by the Real Academia Española: it means ‘knave’ or ‘rogue’ if converted to a noun (in Castilian it is an adjective). It’s possible that the Dominican word is of Taino or West African origin, rather than Spanish.
So, I’d like to ask our non-Anglophone readers, how many words for kinds of adult anurans are there in your language? And how does this compare to the biological diversity?
[The title of the post refers of course to a story about demons in the Gospels. A Roman legion had 6,000 men (and there are about 6000 species of anurans). If each family of anurans should have a common name, there names would not be quite legion, but there would be a lot more than two!]
We have a short but macabre selection of photos today, taken by biologist Lou Jost in his Ecuadorian home (he lives in a national park).
My last submission featured spiders and scorpions from my house. Someone in the comments wrote “…basically I’m wondering, do you live in Hell?”. Well, this submission, like the last, could go either way, depending on the person.
Last night as I went into my bedroom I was surprised to see a fairly lengthy snake stretched out nonchalantly alongside my bed. First time I’ve had one in my house. It was vaguely like a coral snake, so I was cautious about it. Here in the tropics it is harder to tell real coral snakes from their mimics, because there are so many more kinds of both coral snakes and mimics. So I carefully caught it in a flower pot and kept it until today to photograph. It turns out to be a newly described species of false coral snake, Siphlophis ayauma, which was only described in 2014 and is endemic to a small area of the eastern Andes in southern Ecuador. Pretty exciting! See here.
A few weeks earlier I had another visitor, a blue-legged centipede. I do hate these things. This one walked between my feet while I was working at night. I’ve never yet been bit, but I suspect it will be just a matter of time before I roll over one in my bed, or get bit by one hiding in my shoe….
Reader Dennis Hansen, whose photographs of Aldabra (a large coral atoll that’s part of the Seychelles in the Indian Ocean) and its tortoises and crabs have appeared on this site before (see, for instance, here, here, here, and here), has now sent a video of his work on the island’s tortoises, “Ghosts, giants, and resurrection.” It’s a wonderful video made by a man who truly loves his tortoises. (See also his posts on Mauritius here and here.) Dennis’s notes:
Here’s a slightly unusual set of visuals for your consideration for the Reader’s Wildlife Photograps section – in the form of a video.
The video is from a recent private & annual TED-like event here in Zurich, where business people, artists, and scientists get together and discuss ideas and stories presented by artists and scientists. It’s usually great fun and a very broad mix of topics and people. The curator of the event, Rolf Dobelli, generously provided me with an opportunity to share our work with giant tortoises, resurrection, and islands with the audience.
As the talk contains almost nothing but photos (and a few video clips of the giants & what they’re up to!), I thought it could be an interesting semi-personal way to share some wildlife photos with your & your readers.(like you, though, I absolutely hate listening to my own voice, so I hope I remember what I said in case you or anyone else has questions…).
Afterwards, when discussing tortoises with attendants, a lot of people enjoyed touching and examining the carapace I’d brought along, leading to discussions about tortoises and ecology in general. Turns out that show & tell works even for CEOs
