When a red-tailed hawk spotted bird researchers approaching along the South Platte River greenway one morning last week, it flinched and flew away, up from a bog toward cottonwoods hanging over a former industrial waste pond.
The researchers saw it, along with a robin, and recorded their observations on a clipboard.
They were counting all the avian species they could find as part of an intensive “bioblitz” survey that, in the coming months, also will include teams tallying plants, bugs and animals along the trash-strewn river corridor in Denver.
Coordinated by Colorado State University as construction crews build a CSU campus and re-develop the National Western Stock Show site on 250 acres just east of the South Platte, the survey data is building a baseline biological inventory of species as development transforms the city.
Worldwide, an estimated 1 million species face extinction as the climate warms and humans degrade and convert natural habitat. Denver leaders, for decades, have declared restoring the South Platte corridor to a healthy enough condition to sustain fish and wildlife a priority. Mayor Michael Hancock’s 2020 sustainability goals called for the South Plate to be made “swimmable and fishable.”
It still isn’t. State health officials last month deemed water quality deficient with E.coli pathogens at levels up to 137 times higher than a federal safety limit. Yet resilient species endure.
“The overall trend is in the negative. Nonetheless, this allows us to get an idea of how diversity is changing,” said John Azua, bird curator for the Denver Zoo, who led the April 23 survey.
The researchers worked from 13 pre-designated sites along a one-mile stretch of the river where they previously surveyed species in August 2019 and September 2020.
One dimension of the project, Azua said, will be “to see if we can make any changes — any common-sense, purposeful changes — in how we develop and how we live as humans.”
At sunrise last week, the researchers gathered on the asphalt parking lot behind the Denver Coliseum. They were still sipping coffee when Rich Reading, director of research and conservation for the Butterfly Pavilion, spotted a snowy white egret flying overhead.
They began along the bicycle path under an Interstate 70 viaduct as an ambulance flashed and wailed across a bridge, walking past shelters where people experiencing homelessness sleep.
They trudged down from the path, over brown trousers in mud, past a clogged corrugated drainage culvert, and stood on the river banks.
“There are ecosystems everywhere,” Azua said.
Reading saw a cormorant, a coastal species that has migrated inland and multiplied at sites such as a pond by the zoo.
“And five rock doves,” he said.
Zoo employee Robin Carey, holding a clipboard, recorded observations and measured the temperature and noise levels at each site. Industrial beeping of rattling yellow earthmovers, thundering highway traffic and sirens impaired researchers’ ability to hear birds. This forced careful observation using scopes and binoculars.
“We’ve got to learn to live with the natural world,” Carey said. “If we continue to degrade it, it will affect our own welfare.”
Three workmen wearing blue overalls and yellow hard hats hunched over a railing above the river, smoking. Sparrows flitted about in bushes beneath McDonald’s yellow arches. An ambulance flashed atop a bridge. And beyond a fence topped with coils of barbed wire, the researchers hiked down to the river again, over a red-white-and-yellow fast-food straw stuck in the mud.
They saw a beaver, head poking up from the water. It had been knocking down trees.
“Gadwall,” Reading said, a kind of duck. “Two mallards. Two starlings.”
Compared with natural bird habitat elsewhere, the array of species here along the South Platte “is not that diverse,” he said. “A lot of the birds here are exotics. Not native species.”
So far, a team of 20 researchers has documented 24 bird species, 142 plants and 506 insects, according to the data posted last week. The leaders are considering an expanded project in the future, drawing in and training volunteers if possible to cover more ground.
But this spring they’re focused on covering the 13 sites and building their baseline, essential for monitoring any future changes.
“Got a ring-necked dove. And a starling. Both on the wire,” Reading said
Azua yelled. “Hey! There’s an osprey! On that telephone pole.”
“Two black-billed magpies. Perched,” Reading said.
CSU’s Sarah Miley, picking up trash along the route, ranked liquor bottles and discarded face masks most abundant, along with seemingly endless plastic grocery bags.
Azua saw a tiny flash of yellow.
“Goldfinch!”
In bushes along the river, they found bushtits and black-capped chickadees.
The construction work on CSU’s new campus includes efforts to stabilize eroding river banks using burlap matting.
Development along the river may be the main threat to birds and other species, worse than water pollution, Azua said.
“Urbanization. Denver over the last two decades has been increasing in human population and the stresses of that are seen on the land within the city and on the perimeter,” he said.
Restoration efforts have been focused on ensuring sufficient water in the river. A cooperative effort by Denver Water and the Colorado Water Conservation Board promises sufficient flows out of Chatfield Reservoir into the river during dry times for environmental purposes.
But beyond the river’s main channel, species survival depends on “the habitat around it,” Azua said. “Birds and animals, they need habitat. That’s what has been the deteriorating resource. Humans are tough on natural resources… It has been a struggle for years and it will continue to be a struggle.”
North of the National Western site, the river ran dry last week, near where a concrete diversion structure funnels flows into the Burlington Ditch that delivers water to food-growers northeast of Denver.
A great blue heron perched there.
And Azua spotted an avocet, a migratory bird with a rusty orange breast, elongated bill curved upward for scooping insects out of mud, standing by a puddle on the exposed, sandy river bottom.
“Don’t see them that often,” he said.
North of the heavy construction where I-70 crosses the river, researchers observed a greater diversity of birds.
They turned westward from where the river was dry, hiking across the Carpio-Sanguinette Park to a wetlands area where they flushed up the red-tail hawk.
And they bee-lined past concrete foundations from a formerly toxic metal smelting industrial site toward Heron Pond. This has been one of the most polluted parts of Denver for more than a century. Denver Parks and Recreation managers, hard-pressed to obtain new open space elsewhere in a booming, densifying city, have held the pond as a possible future sanctuary for birds and other species.
Heavy metal contaminants including cadmium, arsenic and lead have settled to the bottom of the pond.
As the researchers circled it, they saw dozens of ducks, a heron, egrets, woodpeckers, northern shovelers, geese, a yellow warbler and a half-dozen more of the migratory avocets.
They ended their survey here with that evidence suggesting non-human species can survive.
“It has been a good morning,” Azua said. “We’ve seen a lot.”
