Moose Population Has Swelled At Rocky Mountain National Park
COLORADO SPRINGS, Colo. — The Holzwarth Historic Site in the Kawuneeche Valley on the west side of Rocky Mountain National Park is unusually quiet for a mid-August night. At the height of summer tourist season, the park attracts hordes of visitors — more than 4 million in 2017. But the only noises are the flutter of the wind passing through the leaves of the aspens, the crunch of the gravel under deliberate footsteps and the occasional muted murmur of a park employee’s radio.
Silence was what landscape ecologist Hanem Abouelezz needed as she peered through a stand of aspens at a 4-year-old female moose feeding on a bounty of willow trees in the marshy area just south of the historic site’s buildings.
If all went well, Abouelezz would shoot the moose with a dart containing slow-release anesthesia. The moose would slowly fade into a light slumber as a team of biological technicians employed by the National Park Service took blood samples, measured heart rate, checked for ticks and performed a rectal biopsy.
About an hour after Abouelezz released the dart, she would inject the moose with a reversal drug. The cow will gradually awaken, stand up and return to her night of munching, sleeping and roaming.
Yet, if a crunch became a crack or a murmur became shout, this moose might head for the hills. Abouelezz and her team would leave emptyhanded, without the perfect candidate for her study, the first of its kind involving moose, but with implications that could impact the health of riparian areas throughout the park.
In 1980, only one moose was reported in the Kawuneeche Valley. In 2017, the park reported 30 to 50 on the west side and an increasing number on the east side. They’ve been sighted in every drainage, leading park scientists to ask what types of changes were driving such population growth and what the long-term effects would be.
Last summer, a research team led by Abouelezz transformed their question into an experiment with the goal of fitting up to 40 moose — 20 on the west side and 20 in the northeast side — with collars adjusted to each animal’s neck. The GPS collars allow them to collect data on moose population size, population growth, carrying capacity and habitat use. The moose are also monitored for chronic wasting disease, which has afflicted elk in the park, but not yet moose, as well as other baseline health.
Though park scientists have collared elk in the past, this is the first time the trackers have been fitted to moose.
Thus far, the collars have not left noticeable rubs or marks and don’t appear to be interfering with the moose’s daily activities. The hour under anesthesia, also, has had little if any impact on the moose.
“We do what we can to make the moose as comfortable as possible,” Abouelezz said. “When we’re taking the samples, we make sure it’s spine is in alignment, blindfold it so it has no awareness of human contact and, just in case, hook it up to an oxygen tank.”
In isolation, an uptick in the moose population isn’t a problem. But moose don’t live in a vacuum, just like every other organism in the park, including the humans that visit it.
More moose means more mouths to feed. That means more stress on willow trees, which are 93 percent of a moose’s 55-pound-a-day diet in Rocky Mountain National Park. Again, in isolation, this might not have caused much concern, the team said, since willows evolved with browsers like moose, adapting to their feeding habits to find ways to regrow once their leaves were chomped off, said John Mack, the branch chief of natural resources for the park.
Add disease, specifically Cytospora fungi which is carried by birds, and the equilibrium of the ecosystem is noticeably disrupted. Suddenly, certain areas that used to be populated with a dense mass of tall willow trees are meadows studded with stumpy willow bushes. Their branches, which are now only about 3 to 4 feet long, are naked and dying, even though their core still tries to produce leaves at the base.
Without grizzly bears and wolves — primary predators of moose — the willows have few defenses.
“The infection itself is not out of the ordinary, but it kills the leaves at the perfect level for browsers, which moose are, and we have a lot of it currently,” Abouelezz said.
Willows serve as soil stabilizers in riparian zones, which serve as the interface between land and a river or stream and are critical to watershed health, wildlife habitat and overall ecosystem health. Without such vegetation, the riparian zone can wash away, impacting the aquatic and terrestrial landscape.
“Once you see the whole ecosystem starts to suffer, the red flags go up,” Mack said, probing the empty branches atop a willow.
Earlier in the night, about 5 p.m., a section of Trail Ridge Road just west of the Bowen Brown Trailhead was in what park employees like to call “an animal jam.”
A visitor with an eye attuned to wildlife had spotted a moose about a quarter mile off the road and pulled over for a closer look.