Wildlife viewing opportunities

The reservoir and its surrounding environs provide habitat for a variety of fish and wildlife including bass, catfish, walleye, osprey, raptors, herons, owls, rabbits, snakes and prairie dogs.

Wildlife Guidelines

  • Do not feed any wildlife.
  • Obey all closures and signs. At different times throughout the year portions of the reservoir may be closed to protect nesting wildlife and habitat.
  • Osprey, American bittern, northern harrier and burrowing owl nests are monitored on the west side of Boulder Reservoir and at Coot Lake. Because these are species of concern, the areas are closed to human use. This regulatory closure is from March 15 through Sept. 10 (or Oct. 31 for burrowing owls). The closure area includes water space at the Boulder Reservoir. The closure boundaries are marked with signage both on land and on water (buoy markers).
  • Local, state and federal laws protect wildlife around the Boulder Reservoir.
  • Entering closed areas 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.
  • No person shall hunt, trap, net, impede, harass, chase, kill or remove any wildlife or destroy, remove any burrow, nest or animal dwelling.
  • Horses are prohibited at the reservoir.
  • Fishing regulations follow all state parameters. Please contact Colorado Parks & 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 2019, 36 observers devoted over 660 hours to this effort. The annual Boulder Reservoir Birds of Special Concern Monitoring Report has been completed and a summary is below.

Northern Harrier – Boulder County Rare & Declining

  • A successful nesting in the Dry Creek cattail marsh during 2019 was the third observed in this location since 2004. A successful nesting in the Little Dry Creek marsh was the sixth between 2004-2019. Coot Lake Wetland did not have any indication of harrier territories in 2019.
  • There are many possible reasons for the difference between sites, but patterns indicate that success is less where recreation is higher. For example, Dry Creek has been assessed to be a higher value ecosystem but still has lower success than Little Dry Creek just a mile down the road. One main difference is the increased recreation activity at Dry Creek. Coot Lake has grown in popularity and has the highest level of recreation of the three sites. The wetland is surrounded by a trail that allows off leash dogs and is often illegally entered. Coot Lake hasn’t seen an indication of a harrier nesting attempt since 2005.
  • During 2019, Northern Harriers also were reported nesting in Boulder County in two other locations, but one of those nests failed.
  • These numbers may not be enough to sustain a viable nesting population in this area (Johnsgard 1990, Smith et. al. 2011).
  • Based on recent data, 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

Northern Harriers near Boulder Reservoir

Number of Years (2004 - 2019)
Wetland Area Nest Success Nest Failure Pair Seen - no nest No Indication Fledged Young
Coot Lake 1 0 1 14 4
Dry Creek 3 5 0 8 9
Little Dry Creek 6 4 1 5 24

American Bittern – Boulder County Isolated and Restricted

  • In Boulder County this species is still limited to only about a dozen documented nesting sites, with eight of these in wetlands adjacent to Boulder Reservoir, privately-owned Six-Mile Reservoir, and Coot Lake.
  • During 2019 we saw or heard American Bitterns at four locations (down from six last year and eight the year before) around the Reservoir.
  • Confirming nests or fledged young is difficult for these elusive birds; however, in 2019 we observed young flying over one of our sites which implies the area remains important for this species.
  • 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.

American Bitterns near Boulder Reservoir

Number of Years (2004 - 2019)
Wetland Area Territories Nest with Young Calling or Pair Seen No Indication Fledged Young
Coot Lake 3 1 9 3 unknown
Dry Creek 9 2 3 2 1
Little Dry Creek 5 1 8 2 3

Osprey – Boulder County Isolated and Restricted

  • The Little Dry Creek osprey nest failed for the third year in a row. The Dry Creek nest (which is actually across the street on OSMP) also failed.
  • Productivity within the study area has fallen dramatically, from 2.3/nesting attempt from 2004-10 to 0.8/nesting attempt from 2011-19. During 2017-19, nests fledged only one young. The consultant has recommended a more intensive and more focused nest monitoring to help determine possible causes of this recent spate of nest failures.

Number of Osprey Fledglings near Boulder Reservoir

Nest Platform Area 2005-2010 (6 years) 2011-2016 (6 years) 2017-2019 (3 years)
Dry Creek 18 0 1
Little Dry Creek 8 12 0

Burrowing Owl – Boulder County Isolated and Restricted

  • Burrowing Owls nested successfully at the North Dam prairie dog area in 2004 and not again since. A pair was spotted at the Aeromodel prairie dog colony in 2011 but nesting was not confirmed. In 2017 nesting was successful at this same site. In April 2018 we observed a single burrowing owl repeatedly perched on the same nest burrow but then it disappeared. No owls were observed in the study area in 2019.
  • 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.

Breeding Birds

A consultant conducted more comprehensive breeding bird surveys during 2013 where 113 bird species were observed within the study area, and during 2018 when108 species were observed (Jones 2013a and 2018b). Between 20 March and 30 August 2019, volunteers observed a total of 79 bird species within the study area, including 64 potential breeding species (birds seen or heard within documented nesting habitat during their documented breeding season (Wickersham 2016). Nesting was confirmed for 13 species. Birds observed during 2019 included 16 Boulder County or Colorado Natural Heritage Program listed species (Colorado Natural Heritage Program 2019, Boulder County Comprehensive Plan 2018): Wood Duck, Eared Grebe, American Avocet, Long-billed Curlew, American White Pelican, American Bittern, Great Blue Heron, Great Egret, White-faced Ibis, Sandhill Crane, Osprey, Bald Eagle, Northern Harrier, Bushtit, Cedar Waxwing, and Bobolink.

The full report 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.

2019-20 Avian Winter Roost Report