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Lack of good, summer nutrition may be one reason elk are spending more time on private Wallowa Valley and Zumwalt Prairie land and not in the national forest. KATY NESBITT / The Observer
Researchers John and Rachel Cook conduct ground-breaking work
Decreases in elk herd numbers have prompted agencies and biologists alike to look to their habitat for clues.
A series of studies, started in 1995, reveal a new piece to the puzzle: the importance of nutrition to elk health, reproduction and survival.
While working with a large herd of tame elk in the early ’90s, La Grande researchers John and Rachel Cook of the National Council for Air and Stream Improvement started questioning the importance of nutrition.
“Nutrition is an important mechanism of the animals’ performance that was understudied at the time we started our research,” said John Cook.
Cook said recruitment of calves until adult age classes has declined by about half since the 1950s across the Blue Mountains. With this in mind, the Cooks set out to discover if nutrition is indeed a factor, if so, what’s causing the problems, and to come up with solutions.
Elk are one the most studied wildlife species in the western United States, but the Cooks’ nutrition research was ground-breaking. The fact that elk herds were declining across the Northwest, said Cook, tended to shift the focus away from habitat quality, thermal cover, and roads, to understanding what it is about habitat that drives population dynamics and performance.
The Cooks have used both wild and tame elk for nearly two decades to learn about their nutritional needs. What they discovered is that a small difference in
nutrition has a big effect on
The tame elk study started with 60 elk, all around the age of 4 or 5 years old. They were divided into three groups to determine the effects of nutrition on reproduction.
The research took into account calf growth, yearling growth, yearling pregnancy, adult pregnancy, adult body fat percentage, breeding times, and winter survival.
The results were dramatic. Some of the lactating cows were fed a diet low in nutrients from June to October. In that group, most did not ovulate or breed, said Cook.
Cook said, “When pregnancy rates in elk are reduced, that indicates pretty strong summertime nutritional limitations.”
By measuring body fat in autumn and spring the Cooks discovered summer nutrition determined how fat the elk were in the fall and determined how fat they were coming out of winter. In fact, summer nutrition is more important in determining body fat than winter climate conditions, said Cook.
The Cooks took the tame elk on the road and set them up in enclosures along the Pacific Coast range, the Cascades, and in Wallowa County. Cook said causes of summer nutritional limitations and solutions can best be identified using detailed studies with captive, trained elk. Locally, the tame elk were set up in pens in the Sled Springs wildlife unit and the research was funded mostly through Rocky Mountain Elk Foundation and Boise Cascade.
In the fall, about 30 to 40 percent of the cows that raised calves had seven percent body fat or less; in the springtime 50 percent had less than two percent body fat.
“Those are numbers that indicate pretty significant summer nutrition conditions,” said Cook.
The Cooks also took their research to the wilds and studied 22 elk herds in five states between 1998 and 2010. Elk were captured twice a year to separate summer and winter nutrition effects.
The study shows that summer nutrition is the most important; some of the fattest elk in the study were from Yellowstone which has the harshest winters and deepest snows in the lower 48.
Cook said Oregon Department of Fish and Wildlife helped fund this work. Over the course of the wild elk study, more than 4,000 animals have been captured and the work continues today in Montana.
“It’s the largest data set of live elk body condition that’s ever been collected,” said Cook. “If you are talking about habitat influences and population performance, it is nutrition that is driving the boat.”
Grass can provide good forage in the spring through late May and after the fall rains, but in mid-summer deciduous browse and forbs, like Rocky Mountain maple and willow, are important, Cook said. The research indicates that in the higher elevations, fir species dominate the landscape, and a canopy cover over 50 percent competes directly with shrubs — important forage species.
“The data indicate that some forest management that opens up dense forest canopies will increase the amount of good quality forage for elk. This may be the best way that managers can improve summer forage in the Blue Mountains,” said Cook.
What will it take to provide better elk habitat in Eastern Oregon forests? Cook said land managers have a lot of competing management needs.
“Providing good forage for elk is just one of many objectives managers face.
It’s up to the public and the management agencies to decide the priorities for land management options,” said Cook.
“But the data clearly show that the best options for providing high quality forage for elk will probably require some forest management in the higher elevation fir forests in the region. Management options to improve nutrition in drier, lower habitats are limited.”