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Boulder Reservoir Wildlife

The reservoir offers a great variety of wildlife viewing opportunities.

Wildlife Guidelines

  • Please do not feed any wildlife.
  • Please obey all seasonal wildlife closures and signs. At different times throughout the year portions of the reservoir may be closed to protect nesting wildlife and habitat.
  • Osprey nests are monitored on the west side of Boulder Reservoir near an area referred to as Windsurfer's Point. Because of the rarity of a successful nest site for this species along Colorado's Front Range, the area around the nesting platform will be closed to human use. This regulatory closure is from Feb. 1 through Sept. 10. The closure area is within 300 yards of the nesting platform on land and within 100 yards of the nest site on the water of Boulder Reservoir. The closure boundaries are marked with signage both on land and on water (buoy markers). Please note that entering this closed area may result in a summons to court (fines of up to $1,000 and/or 90 days in jail) and suspended boating privileges at the Boulder Reservoir. Local, state and federal laws prohibit harassment of osprey and other wildlife around the Boulder Reservoir. Note that all birds of prey, waterfowl and all wildlife species are protected under local, state and federal law.
  • Horses are prohibited at the reservoir.
  • No person shall hunt, trap, net, impede, harass, chase, kill or remove any wildlife or destroy, remove any burrow, nest or animal dwelling.
  • Fishing regulations come under the jurisdiction of Colorado Fish and Game Department. Please see the Colorado Division of Wildlife  for more information.

Birds of Concern

The marshes and grasslands surrounding Boulder Reservoir support more nests of Boulder County birds of special concern than any other comparably sized area in the county (Hallock and Jones 2010). Since 2004 we have integrated a volunteer monitoring program.  During 2018, 32 observers devoted 404 hours to this effort.  The annual Boulder Reservoir Birds of Special Concern Monitoring Summary has been completed and a summary is below:

  • Northern Harrier – Boulder County Rare & Declining

    Table: Nesting Season Observations
    • The successful nesting (2 fledged young)  in the Dry Creek cattail marsh (near the model airport recreational facility) was the first observed in this location since 2010.

    • Northern Harriers nested successfully in the Little Dry Creek cattail marsh in 2014, 2016, and 2017 but not in 2018. 

    • Last year we had the only successful Northern Harrier nest we knew of in all of Boulder County.  This year, there was one other successful nest on OSMP property but the Boulder County nest failed.

    • Based on recent observations, Northern Harrier appears to be among the most endangered nesting bird species in Boulder County (see Hallock and Jones 2010). Therefore, every effort should be undertaken to protect and expand potential nesting areas. 

    • Consultant recommendations include:

    • 400 m seems a minimal buffer for Northern Harrier nests, especially considering their nests are located on the ground and vulnerable to disturbance by roaming hikers and dogs.

    • Efforts to restrict all human traffic passing near the Little Dry Creek and Dry Creek wetlands to the existing road right-of-way would further limit disturbance of nesting harriers.

    • Enforcement of parking prohibitions along N. 51st St. during triathlons and other major reservoir of events is crucial to protecting nesting harriers.

    • At Coot Lake, dogs should be leashed throughout the Northern Harrier April-August nesting season, or at least until it has been established that no harriers are nesting, on the trail encircling the wetlands west of the lake.

    • In instances when pairs may choose to nest within 400 m of existing trails or other recreational facilities, seasonal closures of those facilities will contribute to nesting success. Raptors may be more inclined to abandon nesting sites during the nest-building and early incubation periods than during the chick-rearing period (Colorado Division of Wildlife 2008; Craighead and Craighead 1965). The Northern Harrier nesting chronology, below, based on observations at Boulder Reservoir from 2006-14, can inform decisions about seasonal closures:

      • Nest building: 12 April-15 June

      • Incubation: 30 April-26 July

      • Feeding young on the nest: 25 May-7 July

      • Fledged (independently flying) young: 15 June-15 August

  • American Bittern – Boulder County Isolated and Restricted During 2018 we saw or heard American Bitterns at six locations (down from eight last year) around the Reservoir.  The timing of the observations suggests the presence of multiple nesting territories in our closure areas.  Confirming nests or fledged young is difficult for these elusive birds; however, in 2018 we observed young flying over one of our sites which implies the area is important for this species.   
    • In Boulder County the species is still limited to only about a dozen documented nesting sites, with the majority of these in wetlands adjacent to Boulder Reservoir, privately-owned Six-Mile Reservoir, and Coot Lake. 

    • Given their vulnerability to urban-adapted predators and proximity to recreation, strategies that increase the size of marshes and protect them from disturbance by humans and pets should benefit nesting bitterns.

  • Osprey – Boulder County Isolated and Restricted
    • Little Dry Creek failed for the second year in a row.

    • Dry Creek (OSMP) had one fledgling, the first since 2010. 

  • Burrowing Owl – Boulder County Isolated and Restricted
    • Burrowing Owls had not been documented nesting successfully within the study area since 2004 nor even observed since 2011; however,  in 2017, two out of four young successfully fledged from the Dry Creek area. 

    • In 2018 we observed a single Burrowing Owl perched in a prairie dog colony in the Dry Creek drainage 50 m southwest of the recreational aeromodeling facility on 15-26 April (This individual repeatedly perched above and adjacent to the prairie dog burrow used for nesting in 2017. We observed no Burrowing Owls at this site after 26 April.

    • Coot Lake Wildlife Closure AreaElsewhere, 2018 appears to have been the most productive year for nesting Burrowing Owls in Boulder County during this century (Jones).

    • Protection and conservation of prairie dog colonies around the reservoir may contribute to future burrowing owl nesting success, especially if prairie dog colonies are relatively large and buffered from disturbance.

Between March 20 and Aug. 30, we observed a total of 108 bird species within the study area, including 83 potential breeding species (birds seen or heard within documented nesting habitat during their documented breeding season, Wickersham 2016). Nesting was confirmed for 25 species. Birds observed during 2018 included 18 Boulder County or Colorado Natural Heritage Program listed species (Colorado Natural Heritage Program 2018, Hallock and Jones 2010) of importance for conservation. 

The full report pdf includes known disturbances or closure violations and detailed recommendations for management actions, including limiting human use, in each closure area.  

An additional study of winter roosting behavior for Northern harriers, bald eagles and short-eared owls was performed and the report notes a high rate of Northern harrier activity. 

2018-19 Avian Winter Roost Report pdf