National Park Service volunteer Terry Lincoln has been monitoring nesting sites for the past 11 years in Theodore Roosevelt National Park.

“I started on my own time. I really enjoy hiking and camping and watching animals. I checked in with the folks at the park, asking them what I can do to help out,” said Lincoln, who is the director of Bismarck’s Dakota Zoo.

Lincoln’s observations are added to the park’s data base to help rangers interpret the information for tourists, and help the park with management decisions.

Lincoln said golden eagles build nests along the cliffs and in large cottonwood trees.

“By and large, the cliff nests were wiped out,” he said. “Sometimes, birds with a perfectly good nest abandon it. We don’t know why,” he said. “The fun part of it is looking around and figuring out where they went. It’s exciting, like a treasure hunt.”

Lincoln charts observations of the nests from March through July, when the chicks are hatched and flying on their own.

If the eagles are nesting on cliffs, Lincoln sits on a nearby hilltop with a good spotting scope.

“I’ve seen interesting things. I’ve seen prairie falcons attack golden eagle nests. I’ve seen landslides make chicks jump. I’ve seen adult birds feed a rabbit to the little ones,” he said.

He’s also seen golden eagles pick up prairie dogs, small mammals and an occasional snake.

“My wife has been with me a couple of times. I’ve had other people, like biology professors, come along sometimes. I’m pretty much by myself. I like to get out there pretty early in the morning,” he said.

Lincoln has learned that golden eagles are territorial. They generally stay within a range of four miles.

“In the south unit, there are consistently two nesting pairs, sometimes as many as four. The exciting part is figuring out what causes the fluctuation,” he said.

If the nests are abandoned this spring, he’ll search until they are found.

Lincoln hasn’t observed any bald eagle nests in the south unit. He believes they nest closer to Lake Sakakawea.

“I’ve seen them at golden eagle nests. A pair of bald eagles were squawking and carrying on like a gang war. In that instance, the balds were passing through,” he said.

Lincoln’s first priority is the south unit, although he estimates as many as 400 golden eagle nest sites are located throughout the North Dakota Badlands.

“The chicks grow so quickly. Sometimes I check when they are 5 inches of fluffy white. In two weeks, they are black and white and four times bigger. It’s incredible. About six weeks of age, they are almost full grown,” he said.

He said an average hatch is two chicks. Some nests contain one or as many as three chicks.

“By mid-July, the birds are flying and pretty much fending for themselves. I’ve seen one or both adults circling around the youngsters, observing from above. Then the adult goes down and takes a prairie dog. They show the chicks how to do it,” he said.

Because the birds have amazing eyesight, Lincoln doesn’t sneak up to the nests.

“They can see you from a mile away,” he said. “I’m there to monitor. I’m not there to harass,” he said.

Lincoln also looks for prairie falcon nests when he’s out in the field.

“They are much harder to find, since they are just a rock ledge where a bird decides to lay its eggs,” he said.

Lincoln takes photographs with a digital camera, to be used for public presentations.

“It all started out as my own personal interest. But it’s become more and more important for us from a zoo standpoint. One of our main purposes is conservation; the other is research and education,” he said.