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New Mexico State University

New Mexico State University

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Seeds May Tell Tales About Migrating Birds

McGREGOR RANGE - At first, they look like plain brown birds, a common sight just about anywhere, but take a closer look at the chestnut-collared longspur, Sprague's pipit and grasshopper sparrow, and the variety and uniqueness of each begins to emerge.

New Mexico State University student Robin Boyle, left, checks a compass as Martha Desmond, center, an associate professor in NMSU's fishery and wildlife sciences department, and student Clay Bowers set up a grid that will be used in a grass seed study on Otero Mesa. (NMSU Agricultural Communications photo by Darrell J. Pehr)

In the spring breeding season, for example, the male longspur arrives in style, sporting a yellow neck, chestnut nape and black belly. In winter, longspurs form flocks that include hundreds of birds. The flight pattern of a startled Sprague's pipit - straight up into the air for 100 feet - is a sight to see. Even the secretive grasshopper sparrow, which is rarely seen or heard in winter, sings a special song during breeding season - "kip-kip-kip-zeee" - that sounds a lot like a grasshopper, its favorite summer snack.

But the numbers of these and other nomadic, grassland birds, which spend their winters in the Chihuahuan desert of the southwestern United States and northern Mexico, are dropping faster than any other bird group on this continent. Scientists from New Mexico State University are working to find out why.

"These birds are showing population declines more so than any other group of birds in North America," said NMSU's Martha Desmond, an associate professor in the fishery and wildlife sciences department.

Desmond is studying their food supply - grass seeds - on Otero Mesa, part of the winter range of these and other short-distance migrating birds, such as Baird's, savannah and vesper sparrows. Learning how precipitation patterns, grazing pressure, soil conditions and shrub encroachment affect seed production will help scientists understand more about the birds.

The birds breed in the northern Great Plains, then head south for the winter. On Otero Mesa, where this year's late monsoonal rains nourished the huge grassland that stretches north from the Cornudas Mountains on the Texas border to the southern flank of the Sacramento Mountains, their diet relies on a good supply of grass seeds. The seed production study is funded by the U.S. Department of Agriculture's National Research Initiative Managed Ecosystems Program.

Last September, four NMSU undergraduates - Jesse Berryhill of Espaņola, Robin Boyle of Blackstone, Mass., Clay Bowers of Farmington and Kacy Cobble of Las Cruces - dodged threatening thunderstorms and persistent insects while placing 320 seed traps across 16 plots on the McGregor Range, a military-controlled part of Otero Mesa southeast of Alamogordo. Assembled from short sections of PVC pipe, funnels and wire mesh, the traps were set on the ground in a grid pattern. As dropseed grass plants matured, their seeds fell to the ground, and into the traps.

Through the fall, the four students, joined by undergraduates Rene Galindo of Las Cruces and Zachary Schwenke of Albuquerque, gathered seeds from the traps every two to three weeks. Students will also take soil core samples for soil type and compaction, measure soil pH and collect data from rain gauges that measure timing and distribution of precipitation. They will also investigate other methods for measuring total seed production on the plots.

Researchers will examine conditions of the plots where grazing cattle were fenced out, and those that were lightly grazed, as well as measure vegetation composition and cover on the plots.

Soon, the traps will be brought in and students will begin to count and categorize the seeds in the lab, a painstaking process.

The seed study will help researchers understand how environmental conditions and land management affect winter sparrow food supplies. The goals are to learn more about the winter ecology of these declining species and to make recommendations for sustainable land management.

"A lot of grasslands have been invaded by shrubs," Desmond said, and some grasslands have become dominated by the intruders. Those changes can impact birds in more ways than jeopardizing their food supply. The birds are more vulnerable to predators, for example, where grasslands are fragmented. And some birds require a minimum amount of open space during the breeding season, but little is known about the influence of shrub encroachment where birds spend the winter.

The more researchers can learn about the factors that affect seed production, the more they'll learn about these grassland birds. They'll also be better prepared to make valuable recommendations for sustainable land management.

"They're little brown birds. They're hard to study and they're hard to identify," Desmond said. "But it's a really neat group of birds. People don't usually realize the amount of diversity of grassland birds that live in the Southwest during the winter months."