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Excerpts from Jim Conrad's
Naturalist Newsletter
from the September 6, 2018 Newsletter issued from Rancho Regenesis in the woods ±4kms west of Ek Balam Ruins; elevation ~40m (~130 ft), N~20.876°, W~88.170°; central Yucatán, MÉXICO
SHEEP FROG
The rancho's little cement-lined pond continues to be both a blessing and a curse to critters who jump or tumble into its water and can't get out because of its vertical walls. I've added rocks as best I can enabling most frogs and larger snakes to escape but turtles still have to be taken out by hand. I visit several times a week just for that purpose. This week something new turned up working along the pond's edge looking for an exit. At first I thought it was a small turtle, but up closer it proved to be what shown at the top of this page.
It was warty and displayed bulging, toxin-producing parotoid glands immediately behind the eyes like a toad, but its snout was pointier than I'd ever seen on a toad, and its eyes smaller. Most remarkable, though, were the two bladder-like swellings on the back, serving as water-wings. I'd never seen or heard of anything like that in the frog/toad world. Each time I approached, hoping to catch it and get close-ups, the animal would dive and surface someplace else. The only other shot managed, better showing the parotoids, is shown below:
I'd heard of the Narrowmouthed Frog/Toad Family, the Microhylidae, but I'd never seen a member. The family occurs all over the world, with its species varying tremendously in body shape, size, colors and behavior. The family is different from the families to which regular toads and frogs belong to, so members of the family aren't really toads or frogs in the unusual sense, but rather narrowmouthed toads or frogs.
It turns out that in the Yucatan we have one member of the Microhylidae, and that's what's shown in our photos. It's the Sheep Frog, sometimes also called the Sheep Toad, HYPOPACHUS VARIOLOSUS. The species is distributed from south Texas south through Mexico to Costa Rica, and the only reason I got to see this one is that it entered the cement-lined pond and couldn't get out.
For, in Amphibians and Reptiles of Northern Guatemala, the Yucatán and Belize, Jonathan Campbell calls it a secretive frog associated with temporary bodies of water, normally seen only at night, and usually when it's raining. He says that a depression that only a week before was completely dry and lined with deeply cracked earth, after the rainy season's first heavy rains, may produce large numbers of Sheep Frogs. During dry weather they dig into the mud of drying ponds to estivate -- the hot-weather equivalent of hibernate -- until the next rain.
Sheep Frogs take their name from their call, which you might guess is a drawn-out, somewhat nasal baaaaaaaaaaa.... I've heard the call during night rains but wasn't sure they'd be Sheep Frogs, until now.
In our area, if a frog has warts, small eyes and a pointy snout, it's a Sheep Frog. That narrow, interrupted pale line running down the back is distinctive. Also, field guides speak of a "transverse fold" or groove in the skin across the top of the head immediately behind the eyes -- though this trait may not be obvious when the frog is at rest. Our toad doesn't show that line.
Amazingly, I can't find anyone referring to the water-wing-like "bladders" beneath the skin on the toad's back. Maybe these features only show up when the frog has been floating in deep water for some time, not mating or calling. After our frog decided that my frequent approaches were too bothersome, he dove and didn't appear again during the 15 minutes I waited. Earlier, from the way he'd quickly bobbed to the surface after each dive, back-bladders first, I thought maybe the bladders wouldn't allow him to stay below for long. Supposedly, the pond's cement floor offers nothing to hold onto. Maybe in the end he just vented air from his bladders and stayed down.