New West Feature

Montana Osprey Suffering From Unfishable Rivers, Baling Twine, Toxins

By Kate Schwab, 6-24-11

	And osprey caught in plastic baling twine, a nesting material the birds will use when available, even though it can tangle them and kill them. Photo courtesy of Erick Greene of the University of Montana's Project Osprey.

Spring flooding in the Rockies is adding a new challenge to an already struggling osprey population, according to a researcher at the University of Montana’s Project Osprey program.

High, murky rivers have been forcing nesting parents to fly as far as 10 to 15 miles away from their nests in search of clearer mountain streams where they can better spot prey, according to Erick Greene, professor in the Wildlife Biology Program in the Division of Biological Sciences.

“Some of the nests we’re watching, they’re not bringing in fish,” Greene said. “Maybe once every third or fourth day. Some of these chicks are starving.” Because light bends, it is impossible to spear fish by aiming directly at them, he explained. To catch fish, which comprise about 99 percent of their diets, the birds have to target their dives elsewhere, depending on the position of the sun and angle of their flight. An osprey may plunge anywhere from 30 to 100 feet above the water to snatch a fish.

“They’re doing some very sophisticated physics calculations,” Greene said. “It takes a long time to get straight—about half die the first year. They just don’t make it. It generally takes four to six years for an osprey to become a good enough fisher that it can even think about breeding. They don’t usually start breeding until they’re quite old.”

The osprey’s singular dependence on fish makes it especially vulnerable to environmental toxins. The birds were all but wiped out in Montana by the late ‘60s because of pesticide contamination in the state’s waterways. Once DDT was banned in 1972, they bounced back. But there are new trouble signs today.

The actual number of breeding pairs statewide is unknown, Greene said, despite the fact that ospreys build large, easy-to-locate nests close to fresh water. There just hasn’t been a long-term tracking program for them. And while scientists know there is a bustling population along the Clark Fork River, on Flathead Lake and in the Missoula and Bitterrroot areas, they’re puzzled by an unexplained drop in numbers in the Lee Metcalf Wildlife Refuge that hints at deeper problems ahead.

That’s because Lee Metcalf offers the best available long-term data on Montana’s osprey situation. Post-1972, the area “went up to about 25 pairs nesting there,” Greene said. “What’s concerning us, in Lee Metcalf is, for about the last 10 to 15 years, the numbers have been plummeting. They’re almost back to DDT-era levels. We have no idea why that is. It could be mercury, it could be baling twine. We don’t know how widespread this problem is.”

Five years of feather and blood sample testing through Project Osprey has confirmed that most toxic metal levels in osprey chicks are very low, a good sign of improving ecosystem health on rivers such as the Clark Fork, which has a history of mining contamination. But while cadmium, arsenic, copper, lead and zinc are down, mercury is up, and that has human health implications. Mercury is the main reason for fish consumption warnings on many state waterways, Greene noted.

Baling twine in an osprey nest at Grant-Kohrs Ranch in Deer Lodge. Photo by Erick Greene.

It comes from two major sources—old gold mines and coal-burning power plants. Mercury attracts gold flakes, so it was heavily used back in the state’s mining heyday. In the southwestern part of the state, Greene said, a lot of the mercury has been traced to former gold and silver mining operations on Flint Creek, a hugely popular flyfishing stream that flows from Georgetown Lake to the Clark Fork.

The Natural Resources Defense Council reports that coal-fired power plants give off as much as 50 tons of mercury pollution each year. Mercury is a natural coal contaminant. Electricity-generating plants that burn coal are not yet a significant problem in Montana, but with the state’s vast coal reserves, they could be soon. Greene said coal-fired power plants have been linked to mercury pollution in Florida, Chesapeake Bay and other locations in the eastern U.S., and China and India are rapidly building new ones. Scrubbing mechanisms do exist, but, not surprisingly, implementing such processes is expensive.

Another obstacle to the birds thriving: plastic baling twine. Twine is estimated to kill 10 to 15 percent of osprey chicks annually, and it often snares adults as well.

Ospreys love to pick it up from agricultural operations and use it to line their nests, sometimes as much as one-fourth to one-half mile’s worth. To combat the problem, Greene’s team has put together a pamphlet for distribution to area farms and ranches. Rather than burning the polypropylene twine, which can give off noxious fumes, his team recommends picking it up and storing it out of sight in a lidded drum or box.

“Some people hang it on fence posts,” Greene noted. “Don’t do that. The ospreys love that. They come down and say ‘Thank you very much for doing all this work for me.’”

While the ag community has been receptive, he doesn’t know how much the situation has really changed. Ospreys die when their talons and wings get caught, but forgotten twine also snares and kills deer and other wildlife, and cows will occasionally try to eat it and die.

“We don’t know how big an issue or how big a problem the baling twine is,” Greene said. But farmers and ospreys like to set up in similar environments, so the problem isn’t going to go away. “Just add water, you’ve got ospreys and you’ve got agriculture. Within four to five miles of fields, there will be baling twine in the nest, and it will kill osprey chicks.”

Ospreys mate for life and have been known to live two or three decades. They may look like eagles from a distance but are easy to spot because of their white breasts. They usually show up in Montana in late March or April and generally lay one to three eggs each spring; sightings of four chicks in a nest are atypical, but do happen. Parents return to the same nest year after year, adding fresh sticks, mosses and, often, baling twine each time. Eggs take 32 days to hatch, and chicks need about 45 or 50 more days till they are big enough to fly. Chicks may stay with their parents for months after they first learn to fly; tracking programs have demonstrated that the young families often migrate south together for winter.

For live views of nesting ospreys in the Rocky Mountain region, visit: 

Project Osprey webcam.

Friends of Deer Flat Wildlife Refuge Osprey-Cam, Nampa, Idaho

Teton Raptor Center’s Wilson Osprey Webcam, Wilson, Wyo.

Glacier National Park Osprey Webcam.

Dr. Heiko Langner, director of UM’s Environmental Biochemistry Lab, and Rob Domenech, executive director or Raptor View Research Institute, based in Missoula, collaborated with Greene on the Osprey Project.

Kate Schwab is an intern at New West.

Like this story? Get more! Sign up for our free newsletters.