| from the April 11 2010 Newsletter issued from
Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán, MÉXICO CASQUEHEADED TREEFROG Two or three times weekly I hike a little trail into the woods for about a kilometer, to where there's a little orchard with some water troughs set out for wild animals, who here during the driest part of the dry season need all the help they can get. A large water tank is kept nearby, periodically refilled by a pickup truck that makes its way back there, often scraping its bottom on rocks. With a bucket I carry water from the big tank to the troughs, and these days I'm amazed at how fast the troughs are emptied. I've seen deer drinking there, and lots of birds, and coatis and other critters in the general area. This week I checked the big tank to see how much water was left and found inside a little treefrog floating at the water's edge. I knew he was a treefrog because of the large, circular pads on the tips of his toes. You can see him, his head barely out of the water, above. Below the frog's bulging eyes notice the pinkish bulges on both sides. These are parts of the frog's balloon-like "bilobed vocal sac," a vocal sac that bulges on both sides instead of bulging into a single big sac below the throat. The sac is bulging because as I took the picture the frog was croaking, apparently because some splashing I'd done sounded too much like rainfall, and he wanted a mate. I'd never seen a frog like this but with its narrowed lower body and curious head with a conspicuous Y- shaped marking, it was easy enough to identify in Jonathan Campbell's Amphibians and Reptiles of Northern Guatemala, the Yucatán, and Belize. It's the Yucatán Casqueheaded Treefrog, TRIPRION PETASATUS, the only species of the genus in our area. In the picture, notice that the frog's head skin is of a different texture than the rest of the body. It's like a shield atop the frog's head -- the "casque" in "casqueheaded." Casque is another name for helmet. Campbell writes that the species "... finds refuge in holes in trees, where it plugs the opening with its bony casquelike head. The behavior whereby tree holes are plugged in this fashion is called phragmosis. Because the skin on the top of the head is co-ossified with the skull, this frog experiences relatively little moisture loss when sequestered in its hiding places... " Below you can see how sharply defined the head casque is from the rest of the body: |
| Campbell describes Yucatán Casqueheaded Treefrogs as conspicuously absent during most
of the year because they "aestivate" (the summer version of
"hibernate") in dried mud. He says it breeds after heavy rains from late May
through August. Therefore, this little frog somehow was out of his dried-up mud at a time of year when not many others of his species were likely to be circulating. I'm watching to see if he can call a mate into his tank with him. My anthropomorphic judgment is that in the last picture he looks a bit sad, as if he'd finally realized how badly out of sync he was with his cohorts. Yucatán Casqueheaded Treefrogs are distributed from the northern Yucatán south through northern Guatemala and Belize to northern Honduras. With such a limited distribution I'd call him an endemic, and it always tickles me to run across endemics. |
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