A ferruginous hawk perches on a telephone pole just outside the city limits of Longmont.
Since the 1980s, Steve Jones has witnessed the decline of the largest and most diverse ecosystem found in Colorado, the shortgrass prairie. He has watched these prairies get paved over by highways, fragmented by residential homes, and converted into agricultural farms. Today, less than half of the historical range of shortgrass prairie remains.
“This loss of grassland habitat will forever change the dynamics of our local raptor species,” said Jones, a naturalist, environmental consultant, and avid birder.
Grassland birds tend to be hit hardest from this loss of habitat among all species that depend on grasslands, as 53 percent of their population has declined since the 1970s.
Once stretched over 550 million acres, the tallgrass, mixed grass, and shortgrass of the Great Plains formed a connective corridor that spanned from Canada to Mexico. A quintessential ecosystem, thousands of plants, birds, insects, and mammals called these grasslands home. Today, less than 40 percent of this historical grassland remains.
A predator of the plains, the ferruginous hawk thrives in the wide-open spaces of grasslands. The vast environment provides ideal hunting grounds and allows this hawk to spot prey from a distance as it soars hundreds of feet above the ground. But their hunting grounds are in peril, as grassland continues to disappear.
“Plains are getting covered by cement, and as a result, so many of our grassland specialist raptors, like the ferruginous hawk, are starting to disappear,” said Jones.
Fewer than 4000 nesting pairs of ferruginous hawks are left in North America. In Boulder County, the population of this grassland specialist has been on the decline since the 1990s, according to the Boulder County Audubon Society. Their threatened status is directly attributed to the loss of habitat from the plowing of the plains and encroaching city limits.
Named for their rusty coloration of bright orange and brown, ferruginous hawk populations have declined from the loss of hunting and breeding ground habitat.
The addition of roads, oil and natural gas infrastructures, fences, and wind turbines to the grasslands all bring threats to grassland specialist raptors.
Roads disrupt and fragment their habitat, and lead to an increase in bird collisions with vehicles. Fences, especially those with barbed wire, are hard for low-flying raptors to detect and disrupt the openness that grasslands provide. Many become entangled, or even impaled on the wires and are unable to escape.
An increase in oil and natural gas infrastructure directly removes a substantial amount of viable habitat, as the average size of one well pad is approximately 5 acres. It also leads to an increase in noise and collisions with the infrastructure, as well as the introduction of hazardous waste to the water and environment.
Raptors are especially vulnerable to collisions with wind turbines, as their soaring behavior makes it almost impossible to maneuver well and avoid flying into the turbine. In the Great Plains, it is estimated that each individual turbine kills approximately 3 birds every year.
Two juvenile bald eagles fly over a fenced-in grassland outside of Broomfield, Colorado. Barbed wire fences have established new invisible hazards for many grassland raptor species, especially those that are low-flying. These fences disrupt the open landscape that grasslands provide, and result in raptors getting entangled within their wires as they hunt for prey hiding in the low grasses.
Colorado is expected to gain approximately 3 million new residents between 2015 and 2050 according to the Colorado Department of Local Affairs. Over eighty percent of new residents will most likely settle along the Front Range and by 2050 Boulder County’s population is projected to reach over 420,000 residents.
“More humans means more development,” said Mike Sherman, a wildlife biologist with Colorado Parks and Wildlife. “And that is not good for our native bird populations.”
The slightest change to Boulder’s grassland habitat can cause drastic declines in native insects, small mammals, and birds according to Jane and Carl Bock, former professors of ecology and evolutionary biology at the University of Colorado Boulder. In 1994 the two reported that a change of only 5 to 10 percent to Boulder’s grasslands can have significant negative impacts on the overall success of local species.
Increased settlement along the Front Range will only accelerate the decline of grassland bird species, especially those that nest on the ground in prairies and wetlands, as these environments tend to see the most action when it comes to human-driven development.
“Boulder County is losing their grasslands completely,” said Jones.
An American kestrel perches on a telephone wire that runs parallel to highway 119.
A raptor that relies on both grasslands and marshes, the Northern harrier was once a common sight to see soaring above Boulder, but this is no longer the case. It is believed to be the most endangered nesting bird in Boulder County according to CPW. Since 2004, only 10 nests have been a success.
Sherman attributes this decline to the gradual increase of recreational development in harrier nesting grounds, as a number of trails have emerged near their breeding grounds throughout the county. Mountain bikers, trail runners, and even leased dogs are most likely behind the disappearance of Northern harriers in Boulder.
In an attempt to bring back populations of these nesting raptors that depend on grassland and wetlands, Boulder County Parks and Open Space have established a number of seasonal based wildlife closures. Fines upwards of $1000 may be faced if one is caught trespassing, hunting, or disturbing these spaces during closure periods.
Coot lake is home to one of the last known sightings of the Northern harrier in Boulder County. To protect this nesting raptor species of special concern, Boulder County Parks and Open Space started seasonal based wildlife closures in the grassland prairies and wetlands harriers depend on for survival.
Boulder’s burrowing owls have been on a dramatic decline as well, and are listed as threatened species in Colorado. Over the past four decades, evidence of their nesting activity has been reported in only two locations in Boulder County, according to Boulder County Parks and Open Space. Within the past two years, there have been no reported sightings of burrowing owls whatsoever.
“That is absolutely due to habitat loss,” said Andrea Lutz, the education coordinator for the Birds of Prey Foundation. “Burrowing owls live in active prairie dog towns and that is what we keep removing.”
Abandoned burrows provide a safe environment for these owls to nest and raise their young, and the surrounding areas of low vegetation create the ideal foraging grounds for insects. However, Boulder County has removed over 95 percent of this prairie dog habitat, as prairie dogs are pests in the eyes of developers from both an agricultural and residential standpoint.
When a prairie dog burrows into the ground, it leaves an intricate system of deep holes, making the foundation extremely difficult and expensive to not only repair but to build on top of as well. Prairie dogs can transfer diseases to livestock and consume the same type of grass according to BCPOS. Also, if livestock steps into a burrow, the animal may break a leg and have to be put down.
Urban and agricultural development has not only kicked out a number of native grassland raptors, it's also expanded the range of raptor species that thrive in urban settings.
A significant portion of Boulder County's grasslands has been developed over for agricultural, residential, and recreational opportunities. As a result, many prairie dog communities border this urban development, forcing raptors to interact with humans more often. While some raptors thrive in urban environments, this is not the case for our grassland specialist species.
A common indication that urban influences have reached grasslands is an increase in trees according to Jones. Grasslands are defined by their grass-dominated landscapes, no more than 10 percent of the environment should have trees.
“People see trees and automatically think they are a good thing. But not for grasslands,” said Jones.
For many grassland specialist raptors, like the burrowing owl, trees limit the available space to forage for food as well as provide habitat for more predatory species, like great horned owls, to move in. Most burrowing 0wls completely avoid nesting in areas near trees due to the likelihood that a predator will be lurking in the branches.
“Grassland specialists are getting picked off by urban adapted predators,” said Jones.