Ever since I was a kid, I’ve been fascinated by animals’ biological processes and behavior. This time of year, it’s all about reproduction.
One warm, wet evening at the end of April, I heard a loud chorus of trills coming from the ponds down the mountain from my house. It was the end of the breeding season of the eastern American toad (Anaxyrus americanus americanus), and I’d never heard so many trilling here. Although my landlords had told me about a huge boom in toadlets down at the ponds years ago, I’d also never seen any breeding down there. I grabbed a flashlight, my phone (to record the trilling), and my camera and headed down.
The noise was loudest at the shallow end of the trout pond. In the growing darkness, I shined my flashlight around there, seeing about a dozen toads on the bank and in the water. Males were trilling to attract females, filling the sack below their chin with air and vibrating the air for 20-30 seconds.
Two pairs of toads were already in amplexus, where the male gets on the female’s back and hugs her under her forelegs with his front feet. Males have special pads on some of the toes to help the male hang on and to reduce abrasion during breeding. The male will stick to the female for up to 24 hours or until she finishes releasing her eggs — or until she vibrates, indicating he’s not the guy for her.
The males kept jumping on my feet when I moved. This is common during the breeding frenzy, when they respond to pretty much anything that moves, on the chance that it’s a female. That’s why couples in amplexus try to stay completely still: if other males pile on the couple when they’re still in the water, the interlopers could knock the male off the female and drown the female, despite her much larger size.
I didn’t see any eggs in the water yet, so went home, planning to return the next day. The following morning, the rain had stopped but it was still warm, the kind of conditions in which toads breed. Just before noon, after running some errands, I stopped by the ponds. My landlords’ trout-fishing business was in full swing, with the toads ignoring the customers walking around the pond. The males were even more frenzied than the night before, still trilling loudly and jumping on anything that moved in the water, including other males, churning up the water in the process. A few couples were engaging in amplexus, with the females now laying eggs.
The female American toad oviposits (lays) somewhere between 2,000 and 12,000 eggs (sources vary wildly). According to the Pennsylvania State University website, the females’ preference for fishless pools (not the case with this pond), combined with the eggs being countershaded (light on top and dark on the bottom), helps to reduce egg predation.
Unlike most female frogs, which lay clusters of eggs, female toads extrude their eggs one after another, encased in two gelatinous spiral strands. When the eggs are first released, the gel covering them is thin and the eggs can be clearly seen. But the strands soon absorb water, swelling to several times their original thickness and taking on the color of the pool’s substrate. The eggs that had been laid earlier now blended in with the pond’s muddy bottom.
Taking out my new Galaxy J7 phone, which is all that I had with me to take photos, I snapped a few of the toads in various stages of breeding. I then headed home, planning to eat return later with my Canon camera, but for several reasons, I couldn’t.
The toads were done by the following day, but luckily, the photos I had taken turned out better than I had expected. I’d managed to capture most of the breeding stages, and the detail was good — so good that one taken on my phone answered a question that had been bugging me ever since the toads started breeding: how does the male toad, on top of the female and looking away from the eggs as she extrudes them, manage to fertilize such tiny eggs (0.3-0.5 inches in diameter) coming out one at a time such a long string?
Here is a video of the toads breeding:
I had searched everywhere online for the answer, with no success, just finding vague descriptions of the fertilization process. Even watching the process in the pond’s clear water from a few feet away didn’t help. However, in enlarging the photo in question, I noticed that the male’s rear feet were touching, forming a sort of triangle with the female’s legs, and in that triangle was a bunch of the eggs that the female was releasing. Was the male purposefully corralling the eggs to fertilize them more efficiently, or were his legs in that position by accident?
I dragged out one of my favorite herp books in my reference library: “A Natural History of Amphibians,” by Robert C. Stebbins and Nathan W. Cohen. Looking up reproduction, I skimmed through to the descriptions of toads’ fertilization process — and there was the answer, in a section on the Great Plains Toad:
“Restraining of the eggs was accomplished by creating a ‘basket,’ a triangular space formed between the male’s legs and the legs of his mate. . . . As the eggs were extruded, the male used his legs and feet to gather them into the basket, where they were held for approximately 3 minutes.”
Eureka! I added the term “basket” to my online search and found a few other sources that confirmed that the American toad also uses this technique. The first mention of the term “basket” appears to be in a much-cited 1909 article on this species by Newton Miller.
I continued to enlarge the photos, discovering another shot of the same male apparently releasing sperm onto his basket of eggs. Nine days later, the toad eggs hatched, and the edge of the pond where the eggs had been was now black with tiny, squirming tadpoles. Does the pond have another toadlet boom in its future? That depends on whether the many predators down there can tolerate the toxic chemicals the toads produce in their skin, which discourages some predators.
Here is a slideshow of the whole breeding session:
While there’s a lot more to toad reproduction than I covered here, solving that one little mystery about the male’s part was really rewarding. Stebbens and Cohen also wrote that “‘basket’ formation has been observed in other species and may be widespread among anurans.” The anuran breeding season is far from over, so, voyeur or not, I’ll be watching to see whether that is true.
© 2017 Pam Owen
Telling local toad species apart
The eastern American toad is found throughout much of Virginia, except for the tip of the southeast coast. It can interbreed with Fowler’s toad, the only other toad species found north of Bath County in Virginia, according to the Virginia Department of Game and Inland Fisheries.
The two species look quite similar, but the males have different calls: while the American toad trills (also described as a bur), the Fowler’s “emits a discordant ‘w-a-a-a-h” of about one to four seconds,” as it is described in “Amphibians & Reptiles of the Carolinas and Virginia.” Distinguishing the two species when it comes to females can be trickier, but the guide has good descriptions of both species, as does the Virginia Herpetological Society’s website — click on each species’ name to bring up a link to its call.