ASU Research E-Magazine: Resource Management--It's for the Birds!

In a small region of the former Soviet Union, four distinct groups vie for the same land and resources. Each group fights to ensure its own survival and success. Sound familiar? Sounds like ethnic or political strife. Sounds like Bosnia. Sounds like Chechnya or Kosovo or Albania. Try again. The region is Kazakstan. The competitors in this never-ending fight are not impassioned nationalists—they are species of eagles.

Four types of eagles living in one region make for an unusual situation, according to Todd Katzner, a doctoral student of ecology at Arizona State University. “Normally, you might find one or two species of generalist predators. But you don’t have four species with similar biology all living together.”

Except in Kazakstan.

Imperial eagles, golden eagles, steppe eagles, and white-tailed sea eagles live together on the grassy steppes of Kazakstan. Katzner wants to know how the four groups share habitat and food resources in the Central Asian country.

Katzner has spent the past two summers studying the eagles on the wide open plains of the Naurzum Zapovednik, a nature reserve in Kazakstan. The ASU researcher hopes that his work will build on existing ecological theory. He also wants to provide practical information that will help land management around the zapovednik.

During his summers at the zapovednik, Katzner found about 50 active nests belonging to all four eagle groups. He put high technology to work. Katzner used a Global Positioning Satellite receiver to determine the exact geographic location of each nest, then analyzed their distribution with a computer. He found that each species of eagle adapted to the space limitations in different ways.

“Imperial eagles space themselves at very regular intervals. It’s also apparent that they need a lot more space to forage in than what they’ve staked out for themselves,” Katzner says.

“White-tailed sea eagles probably respond to one another, but they seem more willing to clump into groups. I haven’t found Imperial nests that are very close together,” he continues.

Katzner analyzed eagle pellets to find out what the birds were eating.

“Birds of prey eat animals whole. They regurgitate the hard parts—bones, fur, feathers—whatever isn’t easily digestible,” Katzner explains. The regurgitated material consists of hard oval pellets, each about two to four inches in length.

During his summers in Kazakstan, Katzner analyzed more than 3,000 eagle pellets. He collected the pellets near nests or under large roosting trees.

Eagles eat almost any kind of small animal. Katzner’s subjects appear to have narrowed their choices.

“The Kazakstani eagles all eat the same things, but in different proportions,” he says. “Steppe eagles eat voles, lots of mice, and small ground squirrels. White-tailed sea eagles prefer more waterfowl—ducks or coots or grebes. The imperial eagles eat ground squirrels and marmots.”

However, Katzner also observed diet variations within each species.

“An individual eagle’s nesting location determines much of what it eats,” he says. “Imperial eagles nesting close to colonies of rooks will eat lots of rooks. But every individual bird can’t do that. If another eagle already lives near the rook colony, a second eagle will have to go somewhere else.”

Kazakstani eagles provide a wonderful opportunity for research. Katzner says the unique situation is useful for analyzing traditional ecological models.

“There are general models that describe predator-prey interaction,” he explains. “And there are general models that describe competition. Each of the models usually is viewed as a discrete, separate thing. I want to find out just how general these predator-prey models are when you add competition to the mix. What happens if you combine them?”

Katzner also hopes to apply his research to practical problems.

“I want to use the information to better understand how land management is impacting the eagles,” he says. “Land use in Kazakstan is changing rapidly.”

Economic problems are changing Kazakstan’s landscape. For example, lots of agricultural land near the zapovednik has gone fallow simply because farmers have no fuel to run their farming machinery. Marmot squatters stake their claim on the empty fields.

Unreliable electric services present other dilemmas. To keep warm through bitter cold winters, people are cutting down trees to burn as firewood. Tree cutting impacts the forest and its inhabitants.

Katzner plans to spend one or two more summers in Kazakstan. He will continue observing the interrelationships between eagle nest spacing, nesting success, and diet, as well as study how land use affects all of these factors. —Diane Boudreau