Even if enforcement of existing regulations governing land-use change were perfect, grassland conversion would likely continue. There is no legal definition of grasslands and no Mexican environmental laws or programs explicitly protect them.

For now, Calderon -- who's now a contract biologist with the Rocky Mountain Bird Observatory -- and other conservationists are helping ranchers take advantage of more general programs, hoping to both improve the quality of remaining grasslands and prevent sellouts. Because these grasslands co-evolved with wild grazers, carefully managed cattle can actually benefit the ecosystem.

I meet Angel Martinez, a 47-year-old rancher, outside his modest house in the town of Casa de Janos. Clad in jeans and a baseball cap, Martinez hops into our pickup to show us his 3,500-acre ranch. The land, called an ejido, is held communally by 16 ranchers, or ejidatarios. Since 2010, after a university researcher helped the ejidatarios with an application, it has been enrolled in a federal payment-for-ecosystem-services program wherein officials calculate the ecological value of a natural resource and then pay its owner a fair wage to conserve it. The grass here is a billowy blue-green and thick as a horse's mane.

Martinez explains through a translator that each ejidatario receives about $1,300 annually to graze seven instead of 20 cows. Because their calves are now fatter and sell for more money, the ejidatarios earn more than in previous years. Martinez boasts that his ejido has avoided the drought's worst ravages. His neighbors, meanwhile, "have a lot of dead cows."

But few ranchers even know about this program, which in 2010 doled out about $88,000 to protect almost 1.3 million acres of land. Limited funds also keep its reach small: When Martinez's group applied, only 16 out of 85 applicants were accepted because money was short. Theirs was the only grassland. Existing conservation programs tend to focus on forests. A government sign posted on Martinez's ranch reads Derribar arbolado: Don't cut down the trees.

Hoping to help fill the gap, The Nature Conservancy purchased El Uno Ranch in 2005 to serve as an outdoor laboratory for grassland restoration and sustainable grazing experiments. The group imported 36 bison from Wind Cave National Park in South Dakota to reintroduce natural grazers. More recently, it started a grass-banking program, letting local ranchers graze their cattle on almost 8,500 acres of El Uno while allowing their own pastures to recover.

Such advocacy is paying off. In 2009, the Mexican government decreed 1.3 million acres of the Janos region a UNESCO biosphere reserve -- the first official protection for grasslands in the country. Digging new wells or clearing grasslands within its borders is now illegal.

Outreach to Mennonites has been more difficult than other efforts, but there has been some progress. Profauna's Lafon has, through a laborious trust-building effort, convinced some farmers that consulting with environmentalists is in their financial interest. About five years ago, Lafon began working with Mennonites who had purchased 22,000 acres of grassland in Valles Centrales. He measured groundwater levels after they sunk each well, and by the seventh -- after they had cleared only 1,200 acres -- he told them they were on the verge of running out of water. "I went to meeting after meeting after meeting with them," he says, before the leaders agreed to stop the project. He hopes to eventually get all local farmers to approach Profauna for advice before clearing new land.

Panjabi, meanwhile, has been working with the World Wildlife Fund Alliance to obtain an approximately $140,000 grant through it and the Carlos Slim Foundation. If it's approved, part of that money will go toward working with Mennonites to reduce pesticide and water use. Some Mennonites have also begun taking out loans on their own to cover more efficient drip-tape irrigation systems, which use half the water of center pivots.

Soon after my visit with Harms, he brings his family and some friends to El Uno. We stand chatting along the dirt road as the biologists bring over some sparrows that have recently been freed of their transmitters. Harms, his wife and his son each cradle a bird in their hands for a moment before releasing it skyward. As hers takes flight, Harms' wife lets out a small laugh.

Back at the net, the research team closes in on Frequency 227, who has managed to dodge capture several times. Catching a single bird can take hours or days, assuming, of course, that it's still alive. Erin Strasser, the field crew leader, tells me that they have found transmitters atop a pile of feathers, buried underground, and inside an owl pellet. Finally, the exhausted bird snags and the biologists let out a whoop.

Seated in the driver's side of a Nature Conservancy pickup, Strasser records Frequency 227's vitals: 19.4 grams and a fat score of 3 out of a possible 6 -- it's in pretty good shape. Strasser steps out of the truck and bids the bird farewell. "It's been a good run," she says. "Hope to see you again next year." Frequency 227 flies low and then drops out of sight into a patch of grass.

Sujata Gupta, a freelance science writer based in Burlington, Vt., writes about the environment, health and food. Check out her writing at sujatagupta.com.

This coverage is supported by contributors to the High Country News Enterprise Journalism Fund.