‘HE’S HANDSOME,’ I’ll say, or “Doesn’t she have have great markings?” when someone is here visiting, and we’re at the edge of the water gardens. “How do you know he’s a he or she’s a she?” people always ask, and with the most common species in my yard–green frogs (Rana clamitans) and bullfrogs (Rana catesbeiana)–it’s pretty easy, even out of mating season: It’s all in the ears.
The guy up top is a dead giveaway: He’s a green frog (I know, he’s all yellow right now, but his species is green frog). The yellow coloration he adopts in mating season can be just underneath, on the chest (with his back staying greenish or brownish), or it can go all-out, as with this ultra-sexy individual. The frog below? It’s a green frog, too–but look at her ear, or tympanum–that flat disc on each side of the head, behind the eye (not the architectural element by the same name).
If the tympanum in green frogs (or bullfrogs) is larger than the eye, it’s a male. About the same size as the eye or smaller? A female, and this one’s hiding in the semi-shade of some pondside vegetation, watching the antics of the males who are violently competing for her attentions.
In some species (in the tropics, for example) it’s more like it is with many birds: males and females have different coloration. (That’s called being sexually dimorphic, or having two morphologies–physical forms–per species, according to which sex you are.)
And then sometimes, it’s all about size–of the thumbs, that is. In certain species of frogs and toads, sexually mature males in breeding season have enlarged pads on their thumbs. They’re called nuptial pads, and no wonder: The better to clasp their brides with, when it’s time for amplexus. I don’t know if the forward young male in the photo below has nuptial pads, but he sure did get himself a big, beautiful bullfrog girl.