Seasonal closures for wildlife ensure shared lands for birds, bats and people

The City of Boulder Open Space and Mountain Parks (OSMP) normally implements its first round of seasonal wildlife closures on Feb. 1, to protect cliff-nesting raptors such as peregrine falcons, prairie falcons, and golden eagles.

For 2022, the City of Boulder OSMP will implement several seasonal closures to protect sensitive habitats that support many wildlife species, including cliff-nesting raptors, bald eagles, grassland-nesting birds, burrowing owls, and bats. Many of these wildlife species have seen significant declines in recent years, and these seasonal closures are intended to help them successfully reproduce and raise young.

In 2021, these closures helped nesting peregrine falcons to raise 11 fledglings. This is the highest number of peregrine chicks raised on city open space since monitoring began in 1986, and peregrine falcons returned to the Flatirons in 1991.

According to Will Keeley, senior wildlife ecologist, the City of Boulder OSMP was one of the first land management agencies to institute seasonal closure to protect cliff-nesting raptors back in 1984. Since then, almost every U.S. land management agency now implements seasonal closures to protect sensitive and endangered species.

"We have a really extensive data set that we pull from and a large number of volunteers that help us monitor the 12-15 cliff-nesting raptor sites that we manage for at the Flatirons," said Keeley.

Every year 40 to 50 volunteers log over 2,000 monitoring hours specifically helping OSMP staff keep an eye on cliff-nesting raptor territories and nesting sites in the Flatirons. This added volunteer-power also allows OSMP to implement what Keely calls "adaptive management," an innovative and collaborative approach that allows OSMP to work closely with another key stakeholder who utilizes these cliffs and rock-formations-the Boulder climbing community.

"Having this really strong volunteer effort feeds into our adaptive management process which allows us to lift closures early and allow the climbing community to understand that we're keeping an eye on things. If there's no raptors [in a given territory], there's no need for the closure to be implemented after May 15 or June 1," said Keeley. ​​"We really work well together with the climbing community to make sure all this is a collaborative process."

Lifting seasonal closures when no raptors are present means climbers can enjoy routes in the area in the mid to late summer and fall without worry of disturbing nesting pairs. It also means the volunteers and OSMP staff can turn their attention to monitoring occupied sites in the approximately 12 to 15 cliff-nesting raptor territories. According to Keeley, cliff-nesting raptors often come back to the same rock formation and nest each year. Observed and monitored nesting sites allow OSMP to set and maintain their annual seasonal wildlife closures for cliff-nesting raptors based on what sites have been occupied in the last four to five years.

Keeely said it's important for cliff-nesting raptors to be in a "disturbance-free zone" not only for when they choose their nesting location but also while they incubate eggs, a process that ranges from 30 to 40 days, as well as while they rear young.

"In terms of disturbance-free zones, we really want to provide a buffer around humans and around these nests so that human intrusion doesn't come at a spot or time where it disturbs the pair to the point where it impacts the nesting success of the pair or the ability of the pair to successfully raise young," said Keeley.

In addition to the peregrine falcons, OSMP also monitors nesting sites for golden eagles and prairie falcons who also utilize cliff nest sites. Keeley noted that while 2021 was the most productive for peregrine falcons on record since OSMP began monitoring territories, there is a cost to that success.

"Peregrine and prairie falcons do compete for nest sites and, just anecdotally, what we've seen in the past five or so years, is that sometimes these peregrine falcons outcompete prairie falcons for nest sites," said Keely. "As we see peregrines do well in one year we may see prairies do poorly in the same year because they sometimes compete for nest sites."

Another species that the OSMP monitors that can be found at the cliff, caves, and rock formations of the Flatirons, are several species of bats, including fringed myotis and Townsend's big-eared bats. OSMP has specifically limited human disturbance of the bat's maternity colonies where females raise their young.

"One piece is protecting the known point resource which is bat maternity colonies, but also we've learned now with white-nose syndrome that we need to be a little more proactive in making sure that humans don't bring the fungus into these maternity colonies," said Keeley.

White-nose syndrome, a disease that affects hibernating bats, is caused by a fungus. Once a hibernating colony is affected, upwards of 70 to 90% of the bats in the colony will die. According to a 2021 study published in Conservation Biology, white-nose syndrome has killed 90% of three North American bat species in less than ten years.

Several OSMP areas, including Mallory Cave, Harmon Cave, and Seal View Cave, are closed permanently to reduce the chance of people introducing the fungus that causes white-nose syndrome. Other seasonal closures to protect the maternity colonies run from April 1 to Sept. 1 or Oct. 1. Similar to the peregrine falcons' breeding success, in recent years, OSMP has also recorded an increase in the number of pups raised by Townsend's big-eared bats.

"We do annual counts in Mallory Cave. Usually, it's around 25 to 30 bats and the past three to four years we've been counting upwards of 45 to 50, so that's really encouraging to see that local population increase in size just in the last five years," said Keeley.

The seasonal wildlife closures also extend to OSMP-managed grasslands. Here the closures are aimed at protecting burrowing owls, the American bittern (a rare type of heron), and grassland nesting birds such as the grasshopper sparrow, western meadowlark, vesper sparrow, horned lark, lark sparrow, and savannah sparrow. The closures also protect nesting sites for raptors such as osprey, northern harrier, and bald eagles.

Keely said that for ground-nesting birds, OSMP is mainly aiming to limit disturbances by foot traffic from people and dogs in the area. The seasonal closure implements an "on-trail" travel restriction though it doesn't close any of the trails in the area, unlike other land management agencies which implement seasonal trail closures as well. In terms of measuring breeding success, Keeley said that observing grassland birds is not as easy as monitoring raptors.

"It's really difficult and really disturbing to the ground-nesting birds, so we don't do a lot of studies on nesting success and productivity on ground-nesting birds, just because it's a huge effort and may not be worth it in terms of disturbing the species," said Keely.

Instead, OSMP staff utilize songbird surveys in these closure areas as a kind of proxy for ground-nesting bird success.

Bald eagles in the grasslands are another species that have had an observed population increase since the first pair nested on OSMP open space in 2005.

"We now have three [pairs] nesting on City of Boulder open space and almost eight [pairs] nesting on Boulder County parks and open space. That species seems to be doing pretty well in the last 15 or so years since it first came back in 2003," said Keeley.

Keeley points to OSMP's collaborative work with their volunteers and the broader community as a key component of these successes.

"Basically, what we've done in years past is identify various successive habitats and work with the community to develop protective strategies to avoid disturbing sensitive wildlife species," he said.

For more information on OSMP, including how to volunteer, visit http://www.osmp.org. For a map of current wildlife closures with more information, visit http://www.osmpwildlifeclosures.org.