Dryness is a defining condition of West Texas, and to the casual observer, the Llano Estacado can appear an unbroken and waterless prairie.
But the plains are dotted with tens of thousands of natural water catchments. These temporary lakes – called playas – are a critical resource for wildlife, and for humans.
West Texans often have cause to cuss the wind. But in the playas, the wind has done a great service.
Over millenia, it carved shallow depressions into the flatlands, exposing buried clay. The clay becomes impermeable when saturated with rain, and these low spots can hold water for months. The shallow lakes average about 17 acres in size. Most of the playas hold fresh water. But where soil is alkaline, salt playas, or salinas, form.
Playas are found in arid regions around the world. But the High Plains contain 95 percent of the world’s playas – as many as 50,000 ephemeral lakes. Eighty-five percent of these are found on the Llano Estacado. The Llano Estacado stretches from eastern New Mexico and Amarillo to Midland.
Michael Nickell is museum scientist at the Sibley Nature Center.
“I’ve had the privilege of seeing these playas from the air,” Nickell said, “and whenever they hold water, they impress me like little shining gems along the prairie – it’s actually a beautiful sight. You wouldn’t necessarily know it, but if you see it from the air, it becomes very obvious – they’ll be pocketed just all over the place.”
West Texas playas are dry for most of the year. But when rains come, playa-dependent creatures seize the day.
Spadefoot toads set the tune. Burrowed in the soil, the toads can hibernate for a year or more. When playas fill, they emerge, and the males fill the air with courtship songs.
“The sound is just absolutely deafening,” Nickell said, “and they will do a lot of fast living, very quickly, and so it turns into very much of a breeding orgy.”
The action isn’t confined to the freshwater playas. Fairy shrimp burst from long-buried eggs and fill the salinas.
“Those eggs can remain dormant and dry for many many years,” Nickell said. “Then when the right conditions come along, the right amount of moisture, you’ll have a super bloom of them.”
Salt-tolerant brine flies swarm the salinas. Both the flies and the shrimp are a feast for birds.
Playa slopes are a preferred site for prairie dogs. In all, 37 species of mammals, 13 amphibian species, 124 species of aquatic invertebrates and more than 200 species of birds depend on playas.
The Llano Estacado is part of the Central Flyway of bird migration. In spring and fall, the prairie skies are busy with migrating ducks, geese, songbirds and shorebirds.
The playas are the full-service rest stop for these avian travelers – providing food, water and shelter.
“Take for instance, sandhill cranes – they’re specifically going to look for playas to roost in at night for safety,” Nickell said. “So on their way south, they will select salinas all the way from Muleshoe to Midland for their roosting.”
No shelter is fool-proof, however. Hawks, eagles and falcons also frequent the playas, feeding on ducks and other animals.
The Ogallala Aquifer underlies the Great Plains, including the Llano Estacado, and is one of the largest aquifers in the world. A quarter of the nation’s irrigated farmland sits atop it. As humans mine the ancient waters, playas are the only significant source of recharge.
A top layer of caliche covers most of the Llano Estacado, and prevents the migration of water. But when rains fall on dry playas, water flows through cracked clay, along the roots of plants and into the aquifer.
Almost all West Texas playas have been changed by human activity. Some have been reworked as stock tanks. Others are used for farming. Playas catch runoff from oil-and-gas operations and industry.
An appreciation for the playas’ role in the landscape has grown in recent years. The Playa Lakes Joint Venture is a regional partnership of private industry, conservation groups and government agencies. The group is working to preserve playa habitat – and maintains a wealth of information on playas at its website, pljv.org.
Nature Notes is underwritten by the Dixon Water Foundation and is produced by Marfa Public Radio in cooperation with the Sibley Nature Center in Midland, Texas. This episode was written by Andrew Stuart.