Monday, August 24, 2009

Heavy Rain + Amorous Amphibians = Toad Explosion

Tropical Storm Claudette had barely cleared the Florida panhandle when I was back in the woods to check my amphibian and reptile traps, scattered throughout the forest. Some of my buckets, designed to entrap small animals that fall within them, had filled with water due to the recent torrential rain and I set upon them to begin the laborious task of bailing them out. In the distance, I heard a cacophony of sounds I attributed to a noisy mob of crows, perhaps angry at a hawk that came too close.

One of my first captures that day was a large grayish toad streaked with lime green stripes.

As I held it in my hand and peered into its vertically oriented pupils (like a cat), I admired the spadefoot toad, Scaphiopus holbrooki, before me. It was the first I had seen in months. These unique animals spend nearly their entire life safely nestled within their deep underground burrows. There they wait, until heavy rains trigger some instinct within their small amphibian brains, and they are compelled to emerge. Although it matters not what time of year this rain occurs, not just any storm will do; however, a deluge will suffice. And Claudette had provided the perfect conditions.

Spadefoot toads are considered explosive breeders, meaning that when the time is right, they will emerge from their underground burrows en masse and find nearby depressions in the landscape that have filled with recent rainwater. In a flurry of singing, wrestling, and courtship, they will mate, lay and fertilize their eggs, and then disappear back into the uplands as quickly as they appeared, often returning to the same burrow from whence they came. Left behind are thousands of strings of their gelatinous eggs, the only indication of the breeding frenzy that had just occurred.

I glanced at the back feet of the toad in my hand and quickly noticed their namesake spades. Looking like the blade of a tiny shovel, the dark structures on their heels assists them in their burrowing, which they do butt-first.

When I placed the toad on the ground, it took a moment to collect itself and then hopped away into the underbrush. The next bucket I checked had two spadefoots within it, as did the bucket after that. When I peered into the third bucket three toads gazed back at me, waiting to be released. All of the animals had been captured on one side of the trap, indicating that they had come from the same area, but perhaps more interestingly, were all headed in the same direction. As I headed back to the truck, I again noticed the sounds in the distance and was puzzled by both their number and intensity.

Driving to the next site, my eye was caught by a large flooded area in the forest, an area that was dry before the storm. As I brought the truck to a stop and rolled down the window, I was overwhelmed by a rock concert of sounds. The realization slowly dawned on me that the noises I had heard in the distance were not from a massive flock of crows at all, but rather hundreds of spadefoot toads with one thing on their collective mind. I exited the truck and let my eyes wander along the shoreline and within the depths of the pool. Everywhere were toads singing, toads clasping each other and mating (knocking down vegetation in the process) and toads swimming through the water, perhaps females heading to investigate males with impressive calls. And the calls, what a sound to experience. So many species of frogs have beautiful and melodic songs; it’s no wonder how they are able to serenade females with their trills. Spadefoots however, are no Tom Jones. At risk of offending their amphibian sensibilities, I tend to describe spadefoot songs as the sound of dry-heaving.

“hooo ahhhh, hwaaaaa, hwaaaa, hoooahhh”

And they were everywhere. This was surely one of the awesome spectacles of nature that the southeastern United States can provide for the enthusiastic and alert naturalist. Reliably finding spadefoots requires both paying attention to weather patterns and knowing of historic breeding pools. When the conditions are right, one may be treated to quite the show, a show that reveals how subtle features of the landscape may be vital to the persistence of certain amphibian species.

Singing alongside the spadefoots were innumerable oak toads, which sound like baby chickens peeping. These toads also prefer to breed in temporary wetlands, where there are no fish to feed on them or their eggs. The sounds were overwhelming; to make myself heard to my field companion I had to yell over the din. I pledged to return to the site at night, when the bulk of toad activity is thought to occur. If the scene was tremendous at 11:00 in the morning, I couldn’t imagine what the experience would be like after the sun had set.

Although other obligations kept me from returning that night, I visited the site after dark the next day, eager to once again observe the frenzied toads. I donned my headlamp and waders and stepped into the water, hoping to get a close look at some of the amorous amphibians. A few minutes of listening revealed nearly a dozen different species of frogs calling to one another, I identified the boinging noise of barking tree frogs, the banjo call of bronze frogs, and the quick trill of gray tree frogs, among many others. There were also several cottonmouths cruising through the water, likely looking for frogs more interested in attracting females than paying attention to hungry and prowling snakes.

Conspicuously absent however, was any sign of adult spadefoots. I couldn’t believe that the hundreds of toads I had seen wrestling, mating and patrolling the water only the day before had disappeared. But they had. Adapted to sporadic heavy rainfall and quickly drying wetlands, the toads had come and gone in the blink of an eye. Most were likely already back in their underground burrows, patiently waiting until the next downpour to once again reveal themselves to the world. They left behind hundreds of thousands of spadefoot eggs, hard-pressed to hatch and develop into baby toads before their pond quickly dried. Strung along patches of vegetation throughout the pool, the eggs were the only evidence of the massive explosion of spadefoot activity that had transpired just the day before.

Toad photos are courtesy of Michelle Baragona.


Anonymous said...

man, you should have called me. I would have loved to hear that!

Anonymous said...

It's always a treat to experience Spadefoots breeding en masse. Here in Macon County, AL, I'm fortunate to have a large population less than a mile from my house (can actually hear their distant chorus from my front porch). When they're out in force, I go to the site and move individuals from the road as they're slowly crossing it. Even very minimal traffic here (a backroad) takes a surprising toll.

Charles said...

I've only seen one spadefoot toad and it was a western species that a kid had for pet. He lived in Salt Lake City.

I have much respect for anyone who can id frogs and toads by their calls. Don't know if I could.

LA said...

Interesting. When do they eat? do they "estivate" during all that time, or do they just live underground like some salamanders? How do they know when to get out? how do....

so many questions!

and on a completely unrelated note, are you aware of any recorded gynandromorphs among herps?

David Steen said...

Anonymous #2. Glad to hear that you know of your own spot to observe this spectacle. For the follow-up, check out your site about two weeks days after they bred and look for thousands, if not hundreds of thousands, of spadefoot tadpoles. Maybe two months after that, the area will be covered with tiny frogs.

Charles, as with any skill, it is achievable with some practice. Try going to a swamp, listening for calls, and then finding the singing frog...much more interesting than reading a description in a field guide...and probably more effective too.

LA. Good questions. Spadefoots will eat mostly bugs, as long as they can fit in their mouth they are fair game. Spadefoots in the arid regions of the southwest will estivate during the dry periods. I don't think spadefoots in the Southeastern Coastal Plain they will enter such a deep sleep; at night they may emerge from their burrows to grab some insects. Regarding how they know when to emerge, some fascinating research from the southwest suggests that it's not moisture, but actually low-frequency sounds that prompt spadefoots to head to the surface. Sounds you might hear from rain or thunder. Researchers were able to get spadefoots to emerge by running a motor near their burrows.

Regarding gynandromorphs, there are a number of amphibians and reptiles wherein males may begin showing traits of females, but this is thought to be as a result of environmental contamination. I don't think this fits the bill, but it's closest I'm aware of.