Legend, Lore, & Legacy: A Storm of Toads
By Loren M. Smith
Amphibians may hold the key to the fragile ecosystem of the playas.
For six months, the shallow wetlands of the Staked Plains of West Texas called playas have been dry, but in May the distant rumble of thunder signals a change. A cool, moist wind begins blowing from the south. Lightning flashes from the sky to the hard ground, blasting the vast spaces with shimmering cracks and booms. A foot or more underground, toads and frogs and salamanders are listening, feeling the vibrations of the thunderstorm, and stirring in their dark burrows. For months and even years they have been holding their breaths, dormant, waiting for this moment. Fat drops of water begin to fall. Soon it’s raining hard, hard enough to drench the Staked Plains, or Llano Estacado, the largest plateau in North America, with a couple of inches of rainfall. In a land that averages only 15 to 19 inches of rain a year, such a rain means a lot to wildlife. It’s strange that such a dry place can sometimes be such a wet place, but the playas, with their hard clay bottoms that hold water for months, can be transformed in a couple of days from a dry, hard-pan depression to a wetland teeming with life. The most visible of playa wildlife — the shorebirds, ducks, geese and cranes — have left by the time of this rain.
But the life of the playas is marked by other creatures that never migrate, that survive drought deep in the soil of the playas. Toads, frogs and salamanders are key indicators of the health of this fragile ecosystem. The thunder tells them that now is their chance. They must act quickly if they are to leave another generation behind. If the toads emerge from their deep soil hideaways and breed, but the playa dries out before their eggs hatch or the tadpoles change to adults, their efforts are wasted.
This time it has rained enough and the playas will remain wet for a month or two. Within a couple of days of the storm, male toads throughout the playas are inflating their vocal sacs and making their distinctive calls for mates. A day or two after the males emerge, the females show up. The males grab them, and fertilize the eggs expelled by the female. In their breeding frenzy the males often grab other species or even other males.
West Texas amphibians must make the most of the wet times. Toads and spadefoot toads sometimes lay up to 45,000 eggs in a single spawn. Weather permitting, females may breed twice a season, producing tremendous numbers of offspring. Within two to three weeks, the tadpoles develop into small toads that live on land. During an explosive breeding season, so many toads may emerge from the playa waters that it becomes difficult to walk without stepping on them.
Although 13 species of amphibians inhabit the playas, five or six are most common. These include the Plains and New Mexico spadefoots, and the less common Couch’s spadefoot. Unlike true toads, which have warty skins and horizontal eye pupils, spadefoots have smoother skin and vertical, elliptical eye pupils. They are named for the darkened, hard “spades” on their hind feet that help them burrow into the soil.
The Llano has four true toads: the green, Texas, Woodhouse’s and Great Plains toads. The Great Plains toad is the most common. The warty appearance of true toads is created by glands that cover their body and legs but, contrary to folklore, touching these glands will not give you warts. True toads also have two toxin-laden glands behind their eyes that discourage predators. The Great Plains toad and the two common spadefoots are generally responsible for the tremendous numbers of small toads emerging from playas and occasionally marching en masse across roads.
Another amphibian that emerges in large numbers is the only salamander occurring on the Texas High Plains, the tiger salamander. The tiger salamander seems to require a longer hydroperiod (the time the wetland has water) to breed than the other explosive breeders. It has an aquatic form that can exist with gills as long as the playas stay wet. This form can attain a large size, as large as terrestrial adults. The tiger salamander also has a cannibal morph in this aquatic stage, which has a larger, wider mouth, specialized teeth and, as its name suggests, eats other larval salamanders.
Two true frogs, the Plains leopard frog and the bullfrog, live in the playas, though neither is common. These frogs have smoother skin, webbed hind feet and a circular organ inset in the neck skin called a “tympanum,” thought to be used for hearing. The true frogs also have two long ridges running down their backs. The bullfrog is an introduced species and not native to the playas.
Two tree frogs — a misnomer in this land of few trees — occur in Llano playas, the northern cricket frog and the western chorus frog. The chorus frog is much more common. These frogs also have smooth skin and partially webbed feet, but are smaller and ack the dorsal ridges of the true frogs. They also have expanded toe tips to aid in climbing on vegetation. Finally, there is one narrowmouth toad, the Great Plains narrowmouth toad, which is not as abundant as the common spadefoots and true toads. It is easily identified by its pointed head and small, squat body.
When large numbers of toadlets and salamanders emerge from the playa water, they need a large food base. These young amphibians eat vast numbers of terrestrial insects, especially beetles, but often anything they can catch. The adults also eat terrestrial invertebrates, but because of their greater size, can eat a wider variety of insects and, of course, large prey. The sheer numbers of amphibians feeding in the uplands surrounding playas significantly influence the number of insects. Indeed, because many of these insects are crop pests, playa amphibians may help farmers with pest control.
Amphibians are significant predators within playa ecosystems, and they also are significant prey. Aquatic birds such as black-crowned night herons feed on the tadpoles and larval salamanders, while land birds and mammals feed on the adults when they leave the water. Although some toads secrete a poison from behind their eyes to discourage predators, raccoons have learned this and just eat the legs off the toads, often leaving them to die a slow death.
Within the past decade, scientists have noted that amphibian populations are declining worldwide. Global warming, disease, pesticides, ultraviolet radiation and parasites have been identified as causes of this decline, and they may be working in concert. Because little research has been conducted on playa amphibians, there’s no way to compare current populations with those that existed several decades ago. What we do know is that because amphibians are both predator and prey, they are key to the health of playa ecosystems. To protect amphibians we need to protect the hydroperiod of the playas.
The immediate threat to playas, according to research done at Texas Tech University, is the erosion of soil into the water. Despite its dryness, the Llano Estacado is one of the most intensively farmed areas in the world, thanks to water pumped from the huge Ogallala Aquifer. When the areas around playas are cultivated for crops such as cotton and corn, the land is more susceptible to erosion following rainstorms. This soil washes into the playas, shortening the hydroperiod. Maintaining at least some native grass in the playa watershed slows erosion and filters out soil that otherwise might enter the playa.
Studies on the Llano have shown that Great Plains toads feeding in a native grassland watershed had a more diverse diet than toads feeding in playa watersheds with croplands. Great Plains toads in the cropland playas were also smaller. Obviously, the land use around playas is having a significant influence on amphibian communities. Amphibians must have abundant insects to store enough energy to survive long periods estivating under ground during dry periods or winter.
Preserving and restoring some native grassland around playas will help preserve their natural hydroperiods, enabling amphibians to breed. Native grasses also provide a good source of food for the toads, frogs and salamanders emerging from the water. Conserving amphibians through playa watershed management will ensure the preservation of biodiversity in the Southern High Plains of Texas and allow us to witness the explosions of amphibians for years to come. O
Loren M. Smith is Kleberg Professor of Wildlife Ecology at Texas Tech University, where he has been studying playas for the past 19 years. His book, Playas of the Great Plains, will be published later this year by the University of Texas Press.