ESTES PARK — A sharp decline in large aspen trees in Rocky Mountain National Park could impair populations of the birds that nest in their cavities, a researcher said at a science conference Tuesday.
More than one-fifth of the trees used by birds such as woodpeckers, northern flicker and mountain chickadee fell over during a 10-year study that ended in 2006.
The area’s overabundant elk are eating replacement shoots, according to Jeff Connor, a park natural-resources specialist.
“We have a finite number of large aspen, and they’re not being replaced,” he said at the park’s biennial research conference. “The way the trend is going right now, somewhere down the road there is going to be a problem.”
Researchers found 108 of 550 trees with cavities had fallen between 1997 and 2006, and others couldn’t be found, Connor said, citing work by the Rocky Mountain Bird Observatory.
In one stand of aspen in the elk winter range of Beaver Meadows, occupancy of the remaining cavities increased by 10 percent.
“It’s kind of like when you think about . . . the scramble for apartments,” Connor said. “As demand goes up, supply goes down.”
The birds favor live trees that have an average diameter of 13 inches, and typically, the trees have two or more cavities, he said.
“These birds need the larger-diameter trees to nest in, and if those trees aren’t out there, then we might see some of these species decline,” Connor said.
While a number of factors, including drought and disease, are taking a toll on aspen, it is the park’s protected elk herd of about 3,000 that draws the most blame and is the focus of a population-reduction plan.
Preliminary studies this past winter revealed that 87 percent of the cows were pregnant, said Jenny Powers of the National Park Service’s Biological Resource Management Division.
“This is pretty gosh-darn high, meaning they are not pregnancy stressed,” she said.
In the absence of major predation, park officials have initiated a controversial effort to test a birth-control drug on the elk and plan to begin killing as many as 200 of the animals next winter.
Thirteen of the 136 cows tranquilized for the study also tested positive for chronic-wasting disease and were destroyed, although they showed no symptoms of the disorder, Powers said.
Steve Lipsher: 970-513-9495 or slipsher@denverpost.com
