Kiley BriggsViews:
On a warm spring night, fog thick in the air, the forceful trills of American Toads filled my ears. Intent on photographing a mating pair, I slowly circled the shallow wetland. If I made one wrong move, the serenade would stop, and the toads would vanish into the vegetation. After finding a pair posing almost perfectly for a photo, I carefully reached forward to move an obstructing leaf from sight. Just as my fingers grasped the leaf, I felt a clammy wetness squeeze my hand, accompanied by an awkward chirp. A toad had grabbed me and would not let go! Prying his arms from my fingers was no challenge, but it may have proved quite disappointing for the toad. From his perspective, he hadn’t just warded off a spectating herpetologist. He had actually grabbed a possible mate! Frog and toad eyesight, it turns out, leaves much to be desired.
During a frog’s breeding season, the males attract females with a distinct call. For American Toads, the call is a high-pitched trill lasting up to 20 seconds. Spring Peepers peep, and Wood Frogs make a sort of clucking sound. When a female approaches, the male will jump onto her back, press his wrists into her sides, and hold on as hard as he can. This is called amplexus, and he will stay on the female’s back until she lays eggs, which he then fertilizes. Other males may try to push him away or also hop on, and things can get very chaotic. Sometimes, males even hop onto a female’s back before they reach water, letting her carry him the remaining distance.
In these breeding frenzies, male frogs are highly prone to mistakes in their mate selection. Indeed, barely a week after encountering the overzealous toad, I found another latched onto the back of a Green Frog. Terrestrial frogs that breed in wetlands for only brief periods each year don’t have much time to find a mate. While every female frog is almost certain to breed, the same is not true of males. Not wanting to miss their chance, the males will grab almost anything that moves. If it’s about the right size, shape, and color, it’s worth a shot. Odds are, it’s at least another frog, and probably the correct species.
By far, the most stories I’ve heard of frogs latched onto the wrong species include Wood Frogs. This recent comic from Bird and Moon lists a few notable examples:
I can also add floating dead mice to the list. While I lack photographic evidence of most of these claims, this video of a Wood Frog amplexing a trout shows that all of the above is possible:
So, what happens when a male frog tries to mate with something other than a female of the same species? He may hang on for quite a while, waiting patiently for it to lay eggs. If it’s a salamander, dead mouse, or human hand, he will need to wait a long time. By far, the things male frogs most frequently grab onto by mistake are each other.
Male frogs might stay at their breeding site a week or more, while females stay only long enough to lay eggs. Consequently, males can vastly outnumber females at breeding wetlands. If they can’t tell a female apart from a floating mouse, you can imagine how often they might amplex each other. They have a system for that, however. Males of many frog species have a release call, which they use when another male grabs them from behind. The release calls are quite cute, actually, often consisting of adorable chirps and gentle vibrations. To the other frog, the message is understood: “You won’t get any eggs out of me.”
Salamanders don’t make release calls, however, and neither do female frogs (correct species or not). Dead fish, pinecones, and cattails especially don’t issue release calls. I’m not sure how long it takes male frogs to figure out they’ve made a mistake in those cases. While they are highly determined, it wouldn’t surprise me if they aren’t very patient either.
While the mating strategy of these frogs seems far from perfect, it has served them well for millions of years. Depending on species, a female frog lays between hundreds and thousands of eggs every year. Despite the apparent shortcoming in male eyesight and mate selection, somehow, almost every single egg gets fertilized.
Already this year, Wood Frogs have begun mating in southern parts of their range, including Georgia. Over the coming weeks and months, the breeding season will spread northward, reaching my home in Vermont perhaps during April. If you have a chance to visit a wetland when they, or other frog species are calling, keep your eyes open for unexpected pairings!
