In the decades since Pitkin County began monitoring the conditions at North Star Nature Preserve, the area has seen two concurrent phenomena: the explosion of river-based recreation and the slow return to more native habitat for the area’s wildlife.
A report, released this month, by Jonathan Lowsky of Colorado Wildlife Science analyzes field data collected in 2020 and 2021 at North Star; the report is meant to document what types of species are using the nature preserve — as well as when and how they are using it — and to “determine the effectiveness of current management in balancing human use with protection of biological diversity,” it reads.
Pitkin County Open Space and Trails, which oversees management of North Star, is gathering data to update the area’s management plan next year. This is the third such wildlife survey commissioned by the county. (The other two were done in 2014 and 2017.)
The data from Lowsky’s report highlights a few areas of concern — including the decline of red-winged black birds and the fact that there are no current great blue heron or red-tailed hawk nests on site — but largely shows that habitat is improving and a wide variety of wildlife use the nature preserve.
Lowsky has been studying North Star since 1998, when he was working as an ecologist for Pitkin County, and he wrote the 2000 management plan for the property. He has since created an independent wildlife biology consulting company, which the county now contracts with to study many of the area’s open spaces.
“North Star is in incredible condition compared to what it was then,” he said. “A lot of that has to do with just the natural resilience of riparian systems.”
For many decades prior to Pitkin County’s acquisition of North Star in 1978, the narrowleaf cottonwoods and willows that dominate much of the land’s river-based ecosystem had been removed to maximize space for hayfields and grazing; the land was a ranch owned by James H. Smith since the 1950s.
Once the land became public and that clearing stopped, the riparian vegetation has had a chance to recover and reproduce.
“The other major architect of the recovery has been beavers,” Lowsky said. “Once people stopped shooting and removing beavers, they have recovered substantially.”
Beaver cuttings of willows and cottonwoods frequently float onto the sandy shores of the river. Since these species reproduce vegetatively, when the cuttings land in hospitable conditions along the shores, roots begin to develop and new plants can grow from pieces of the old.
“The net result is that the percent cover of willows and cottonwoods, and secondary shrubs like alders, along the Roaring Fork and its various oxbows, has grown exponentially,” Lowsky said. “The benefit of that is it’s created orders of magnitude more habitat for songbirds and small mammals, cover for deer and elk, as well as midsize carnivores like weasels, mink, bobcats, coyotes, foxes.”
High percentage of sensitive bird species, and decline in red-winged blackbirds
The resurging habitat at North Star is host to 52 bird species, 32 of which are considered species of conservation concern by at least one agency or organization, according to the report.
Bird diversity is higher than previously detected at North Star, and bird species that are known to be sensitive to human activity are thriving.
Lowsky calculated the ratio of specialist or sensitive bird species, such as fox sparrows and Western flycatchers, to that of more generalist species, such as magpies and crows. He found that there are 4.4 sensitive birds to each 1 generalist at North Star Nature Preserve, a ratio that falls above the mean and median calculated from 2001 to 2008.
Lowsky said this shows that current management is not causing habitat loss for the more sensitive species and notes in the report that habitat conditions have actually improved.
Improved habitat is the aim of management, says Liza Mitchell, Pitkin County Open Space and Trails natural resource planner and ecologist.
“That (ratio) says, as a whole, this property is starting to provide really important habitat for sensitive species,” Mitchell said.
Even as habitat improves, there are a few data points in the avian surveys that speak to a more complex picture.
Great blue herons had a colony at North Star for at least 28 years until 2018, but they haven’t nested on site since. Lowsky’s report noted that the herons’ departure coincided with both a sharp increase in river-based recreation and a decline in the health of the trees in which the birds nested, caused in part by their droppings.
“Overall, great blue heron nesting habitat conditions have declined at North Star over the past few years due to both the increased recreation and natural processes (e.g., heron guano acidification of soils often kills nest trees over time),” Lowsky wrote in the report.
Herons continue to hunt in the wetlands, and Lowsky noted that the county’s efforts to restore the fen at North Star and protect nesting habitat make it “feasible that great blue herons could return to North Star in the near future.”
Lowsky also detected a statistically significant decline in red-winged blackbirds, which the county uses as an indicator species for the health of North Star’s emergent wetlands. It’s not clear why the birds’ presence at North Star is declining even as the amount of wetlands at the preserve is increasing since the county recently plugged drainage ditches in the fen.
“That is happening in other places in Colorado and the West — and I’m not sure why,” Lowsky said. “It does not appear to be due to any management at North Star.”
Mitchell said the decline in red-winged blackbirds is reflective of a large-scale decline across the nation and reveals the limitations of one property in conservation efforts. Red-winged blackbirds depend on emergent wetlands, which are those with plants such as cattails growing up out of them, and are impacted by climate change and pesticides. The blackbirds’ wintering habitat includes areas that are heavily dependent on agriculture.
“There’s pest control for crop damage that’s happening in their wintering range,” Mitchell said. “If habitat loss is one of the threats and impacts to them, restoring the fen should help, but that’s a pretty small footprint compared to their entire wintering grounds.”
Elk and deer use North Star in high numbers; recreation impacts remain a concern
Colorado Wildlife Science detected more evidence — typically by counting scat piles — of elk and deer in 2021 than in the two previous surveys. This comes even as Colorado Parks and Wildlife, which conducts aerial surveys to count elk populations, has expressed concerns about northwestern Colorado’s elk herds.
In 2021, Lowsky counted 221 detections of elk, up from 71 in 2017 and 149 in 2014. There were 68 detections of mule deer in 2021, up from 28 in 2017 and 54 in 2014.
Variations in weather conditions, such as the depth of snowpack and timing of snowmelt, probably contribute to year-to-year differences.
“Whatever the reason, the fact that elk and deer sign was encountered in greater numbers and concentrations indicates that current management is, at the least, not negatively affecting their use of the property,” Lowsky wrote in the report.
North Star has long been recognized as important transition habitat for elk and deer, and Lowsky said the most recent surveys show that elk are using the preserve year-round.
In addition to the detection data, Lowsky also uses data from wildlife cameras, which included photos of very young spotted calves. It’s not clear that elk are actually calving at North Star, but they are raising young there and spending time on the preserve in summer months rearing young.
“North Star is more important to elk than we thought,” Lowsky said.
The camera data is also showing that there are more deer using North Star in the summer months than was previously known.
“I do think that is directly related to the increase in shrubby cover, specifically the willow cover at North Star because it gives them orders of magnitude more hiding cover,” Lowsky said. “When I’ve been out there doing work, I’ll come through the willows and boom, just come across like three deer just bedded down in the willows. If I hadn’t walked where I practically stepped on them, I’d have no idea they were there.”
This vegetative cover is particularly important given the high numbers of people who visit North Star in the summer months.
“Despite the numbers of people out there, they feel comfortable,” Lowsky said. “They can be out there foraging.”
North Star’s moose population continued to grow, too, with six detections in 2021, up from none in 2014 and two in 2017. The data confirms what river users at North Star have seen in recent years — many more moose are using the preserve, and Lowsky encouraged ongoing efforts to minimize conflicts between people and wildlife.
Most of the wildlife activity at North Star happens near dawn and dusk and a bit after. In contrast, the vast majority of recreation on the river is during the heat of the day. To date, Michell says, this difference in usage time has meant the property continues to serve as efficient habitat, even as it grows in popularity with people paddleboarding or playing at the beach.
“We want the animals to be able to use the property. We want them to forage there, breed there, rear their young there and not be impacted by the people that are using it,” Mitchell said. “It seems like they’re able to do that.”
There are species that might be more heavily impacted by human recreation than the report identifies, Lowsky said.
Some of the species that are negatively impacted by human recreation — like spotted sandpipers, waterfowl like ducks, and other smaller shorebirds — aren’t present in large enough numbers at North Star to provide clear data.
Weather dictates when birds arrive and use North Star; one really wet and cold spring might distort data when surveys are conducted, as the current management plan recommends, every three to five years.
In the most recent report, Lowsky recommends completing wildlife surveys at least every three years, with avian monitoring every other year to develop more data points.
The monitoring process is robust and also time-consuming and expensive. The county spent $39,000 on the data collection, analysis and recently published report — work that began with surveying in 2020.
Wildlife activity shifts aways from grasslands toward aspen forests
Although detections of wildlife are increasing, the report notes changes in where the animals are.
In all three survey years — 2014, 2017 and 2021 — the greatest number of wildlife detections occurred in North Star’s grasslands. Over time, though, wildlife appears to be using grasslands less and aspen forests and sagebrush more.
Mitchell and Lowsky each have some theories about why this may be, but Mitchell is quick to point out that this type of data sparks investigation and raises more research questions for the future.
Mitchell noted that she has identified, in the county’s separate monitoring of vegetation, a decrease in native grass species in the grasslands as the invasive reed canary grass, a species that doesn’t have much value for wildlife, spreads. It’s important, she said, to make connections across studies and continue to monitor both the vegetation types and the wildlife use.
One theory is that an increase in reed canary grass has an impact on wildlife use, but Mitchell pointed out that a variety of factors could be leading to the change. Wet years that leave the grasslands oversaturated could push animals elsewhere, or the willows could be getting too thick for deer and elk to easily navigate. The aspen forest and sagebrush quality could be improving enough to draw animals.
Lowsky has another theory about the shift in habitat use.
“That could be because of the river-based recreation,” Lowsky said. “The animals are still there, but they’ve shifted a bit to where they have more cover.”
With no smoking gun, the data becomes part of a larger question that Open Space and Trails staff will need to address in the coming update to the North Star Nature Preserve management plan: How can native habitat be best supported?
The answer, Mitchell said, isn’t always in heavy-handed projects that include more human interference on the landscape.
“Our approach is to support ecological resilience,” Mitchell said. “I want as many native species — flora and fauna — to be able to live and thrive on our open spaces as possible.”
That can be simple, such as when Open Space and Trails acquires a property and stops practices that damage native ecosystems, but ecology often presents more complex challenges.
“It takes a big dose of humility to decide what is an actionable step,” Mitchell said.
Lowsky issued 13 recommendations with his report, many of which involve continuing current actions such as monitoring and studying the area; keeping the west side of the river closed to recreation; and maintaining habitat. He also suggests that Open Space and Trails develop a gray wolf policy for North Star and other properties and allow natural predator-prey interactions between wolves and deer and elk if and when wolves arrive in the Roaring Fork Valley.
Aspen Journalism is a nonprofit, investigative news organization covering environment, water, social justice and more. Visit http://aspenjournalism.org.
This Aspen Journalism original story was published in the July 22 edition of Aspen Daily News.