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Hot Stuff, Spring 1997

The following "Hot Stuff" articles appeared in the Spring 1997 issue of New Mexico Resources:


[Caldwell: Concentrating on cormorants.]Cormorants Combating Mercury

Double-crested cormorants living at two New Mexico reservoirs are dealing fairly well with a fishy situation, biologically speaking.

The web-footed birds feast on fish contaminated with mercury at Caballo and Elephant Butte reservoirs. But a recent study shows the cormorants are getting rid of the toxic metal through their feathers.

Colleen Caldwell, a fish biologist with the Cooperative Fish and Wildlife Research Unit at NMSU, and graduate student Mary Allison Arnold studied the degree to which the birds accumulated mercury from their diet of fish.

The study is part of Caldwell's research on how mercury is transferred up the food chain, affecting the reservoirs' ecosytems. Although scientists have known about mercury levels at Caballo and Elephant Butte since the 1970s, they still aren't sure where the metal is coming from.

What they do know is that mercury can become a problem because it "biomagnifies" through the food chain. "That means plankton (microscopic plants and animals) that accumulate mercury are eaten by small fish, then bigger fish eat the smaller fish," Caldwell explains. "The mercury concentration increases up through the food chain and eventually reaches humans."

At high concentrations, mercury can cause nerve tissue damage and birth defects.

According to the New Mexico Fish Consumption Advisory, mercury levels are high enough that pregnant and nursing women should avoid consuming fish-eating fish like walleye and bass caught in Caballo and Elephant Butte. Some levels are so high that men are advised to eat no more than one fish a year. The advisory is published by New Mexico's health, environment, and game and fish departments.

In their study, the researchers collected cormorant eggs to analyze the mercury levels the eggs received from mother birds. After the chicks hatched, the researchers took blood and feather samples to find out if mercury levels increased during the early stages of the birds' lives when they grow fast and eat a lot.

"We found that cormorant chicks did accumulate mercury from their diet of fish, mostly young gizzard shad and young white bass," Caldwell says.

But the researchers also found that the birds can excrete the mercury. "The birds were able to eliminate nearly all of the mercury burden into their feathers," she says. "It's a good way to get rid of it."

In the feathers, the mercury is no longer "bioavailable" or harmful to the cormorants or other living things.

The researchers focused on the abundant cormorants as a model for other fish-eating birds at Caballo and Elephant Butte, especially the threatened bald eagle.

"It's good news that the birds have a way to deal with the mercury contamination," Caldwell says.



[Banded Rock Rattler] Army Monitors Intruder's Movements

A western whiptail lizard scurries across the desert searching for a meal of insect larvae, beetles, and termites. The little, brown, spotted reptile carries on its daily routine, not knowing the U.S. Department of Defense is tracking its moves.

In 1989, the U.S. Army at White Sands Missile Range (WSMR) began collecting data on the number and distribution of herpetofauna (lizards, snakes, and amphibians) in the area to determine the effect military land use has on wildlife. In 1990, the project was turned over to the Cooperative Fish and Wildlife Research Unit, housed at NMSU.

"People may not realize it, but sometimes munitions explosions cause small wildfires," says Phil Zwank, director of the co-op research unit. "The Army wanted to know what effect their activities have on the surrounding wildlife and how long it takes for animals to return to disturbed areas."

To detect changes in herp numbers, NMSU researchers must first determine the current population of lizards, snakes, and amphibians on WSMR.

"Since 1991, students have been collecting data during the summer months when these animals are most active," Zwank says. "To date, 56 herpetofauna species have been documented on WSMR."

Various live traps are used to get an accurate species count, including five-gallon buckets buried in the ground flush with the soil surface. Researchers also capture the creatures by hand and use glue board traps. All animals are identified, recorded, and released, Zwank says.

The whiptail lizard was the most-collected species, accounting for 51 percent of all animals captured. "This is probably because they are active foragers and are highly mobile," says Sean Austin, a graduate student in fishery and wildlife sciences involved in the survey.

All other types of lizards made up the second most commonly collected group, followed by snakes, toads, salamanders, and turtles. "However, in 1993 and 1994, more snakes and other lizard types, such as the prairie lizard, were collected than whiptails," Austin says. "It's difficult to determine species' populations on WSMR, because the most active animals are easier to capture."

With this reconnaissance mission behind them, the Department of Defense can now examine how the Army's daily operations affect another army - an army of whiptails, rattlesnakes, and spadefoot toads.



[Oryx]Good Grazing Companions?

You've seen them grazing along the roadside between Las Cruces and Alamogordo. The oryx, those large, straight-horned African antelope, seem to have adapted well to their new home on the White Sands Missile Range. But how are they getting along with the neighbors? Raul Valdez plans to investigate.

Valdez, a professor of fishery and wildlife sciences at NMSU, recently began a research project to find out whether the exotic oryx are competing with native New Mexican animals for food. "Exotic or introduced species are categorized as either facilitators or competitors," Valdez says. "Facilitators don't decrease the availability of resources for another species, while competitors do."

Ninety-three oryx were released on White Sands Missile Range (WSMR) between 1969 and 1977. The New Mexico Department of Game and Fish initiated the release to earn additional money for the state through trophy hunting, Valdez says. WSMR was chosen as a site where oryx wouldn't compete with domestic livestock and the population could be controlled with annual hunts.

"That population has grown to an estimated 1,500 to 2,000 animals, and annual hunts do keep the population in check on the missile range," Valdez says.

The problem is that the oryx aren't confined to just the missile range. They have spread out approximately 100 miles in all directions to private land and land managed by the U.S. Army, National Park Service, Fish and Wildlife Service, Department of Agriculture, and Bureau of Land Management. Oryx have been sighted as far south as Otero Mesa on Fort Bliss and as far north as Sevilleta Wildlife Refuge north of Socorro.

As their home range increases, conflicts arise where oryx come in contact with sensitive plants and animals, public recreation facilities, and ecological research sites, Valdez says. Oryx may compete with mule deer and pronghorn for food that can be scarce in the Chihuahuan Desert. With their sharp horns, the exotic animals have attacked automobiles at White Sands National Monument.

By studying the oryx's eating habits, seasonal movements, and general behavior patterns, Valdez hopes to find out whether the exotic species can coexist with the native wildlife. The study is expected to take five years to complete. "Knowledge of oryx movement patterns and herd structure is important in planning their removal from unwanted locations," he says.