The Marvelous Spadefoot Toad

FOCUS NATURE MEET THE IRREPRESSIBLE SPADEFOOT TOAD

aah, baah, baah! The noise coming from my backyard sounded like the bleating of a young sheep or goat. Curious, I pulled on a slicker - the first heavy July monsoon rain was just subsiding grabbed a flashlight, and went searching for the source of this strange sound. A depression in my landscaping had formed a pool, and the calls were coming from the water's edge. In the flashlight's beam, I could just make out a small form sitting half-submerged, its vocal sac inflated like a tiny balloon.

I had met my first Couch's spadefoot toad.

How did it get into my yard past the sturdy block wall fence? Perhaps under the wooden gate. I caught the intruder and carried it to the light on the back porch. The glow of the lamp revealed a mottled olive-green and yellow back and a white stomach. But what caught my attention were the dark fingernail-like projections on the inside of its back feet.

Later, Dr. Mark Dimmitt, curator of the plant department at the Arizona-Sonora Desert Museum, told me this sharp-edged digit, called a metatarsal tubercle, is the "spade" that gives this genus (Scaphiopus) its common name and it explained how my visitor entered the backyard.

Spadefoot toads use their built-in shovels to bury themselves deep in the ground, where they escape the desiccating heat of our desert summer. They corkscrew themselves into the soil and can disappear from sight quickly.

So my friend had buried itself. But what woke it from its subterranean sleep?

Like most amphibians, spadefoot toads need standing water in which to lay their eggs; they emerge with the coming of the Southwest's summer monsoons, which leave pools of rainwaterter. Dimmitt, an expert on spadefoots, has found evidence that they respond to the low-frequency sound of raindrops striking the surface of the ground. The males, which do the calling, appear first, sometimes traveling long distances to reach a pool. Then their song of love begins: on a still night, a chorus of males can be heard nearly a mile across the desert, attracting any females in the area. After a hearty mating embrace, the two swim around the water, the male fertilizing the eggs the female deposits on vegetation or on the bottom of the pool.

One or two nights of such activity may leave thousands of fertilized eggs. Survival requires that many, for most never make it to maturity. Sitting in the summer sun, desert pools may reach 85° to 100° F. In the warm water grow microorganisms that nourish the tadpoles, which hatch in 36 hours and take 10 to 15 days to grow into young toads. But that same heat will dry up the puddle and 10 days is a long time for a rain pool to last in the Sonoran Desert. In the very likely event that the water evaporates too soon, the young will die.

Yet some survive to live 20 years or more. They hop away to spend most of their adult lives in subterranean torpor, five feet or more belowthe surface of the Earth. Occasionally, when temperature and humidity are right, they emerge to feed on insects, spiders, and other arthropods; a night or two of foraging can hold them for a year.

One of their staple foods is a variety of termite. Large numbers of these insects, whose high fat content provides a rich energy source for toads, conduct their twilight nuptial flights at the same time the spadefoots emerge to breed.

Over the centuries, spadefoot toads have adapted to the Southwest's harsh environment in ways that allow them to succeed where water-loving amphibians usually cannot exist. Here they thrive. And when the summer monsoons come, the night air carries the toad's rain song: a celebration of life.

Wallace R. Cromwell is the former director of the Interpretation and Education Department at the Arizona-Sonora Desert Museum. T. A. Wiewandt is a Tucson-based natural-bistory photographer and filmmaker.

After a cloudburst, spadefoot toads abandon their subterranean hideaways to ensure the future of their species. (CLOCKWISE FROM OPPOSITE PAGE) An adult spadefoot emerges to search for pools of water in which females lay their eggs. A male sings to attract a mate. A tadpole feasts on a fairy shrimp. The tiny spadefoot toadlet is ready to go out into the world, albeit underground.TEXT BY WALLACE R. CROMWELL PHOTOGRAPHS BY T. A. WIEWANDT