The St. Vrain Creek corridor comprises the river channel and riparian habitat starting at Steamboat Mountain (N. St. Vrain) and Hall II (S. St. Vrain) and ending near N. 119th St. in Longmont. This area offers a notable concentration of wildlife, unique biodiversity, and vital habitat to “species of special concern.” The stream corridor features cottonwood‐willow riparian groves, cliff faces, and grassland habitats. According to Boulder County’s Critical Wildlife Habitat Descriptions, species of special concern that are known to occur here include golden eagle; bald eagle; plains topminnow; common shiner (state threatened); Iowa darter; stonecat; great blue heron; black tailed prairie dog; American beaver; and the endangered Preble’s meadow jumping mouse (see Critical Wildlife Habitat #7). Threatened Ute ladies’-tresses (a type of orchid) are also found in the area. Recently confirmed sightings of the state threatened Northern river otter are an encouraging sign of the improving health of this ecosystem, which should not be jeopardized by industrial activities in the area. The Critical Wildlife Habitat Descriptions document lists other species of special concern as potentially occurring in this habitat.

The Boulder County Comprehensive Plan (BCCP) includes a number of maps that illustrate biodiversity across the county. The BCCP Critical Wildlife Habitats & Wildlife Migration Corridors Map [PDF] reveals that the St. Vrain Creek corridor is considered a critical wildlife habitat, described as “an area of unique habitat which has a crucial role in sustaining populations of native wildlife and in perpetuating and encouraging a diversity of native species in the county. The area may be significantly productive habitat or particularly vital to the life requirements of species that are critically imperiled or vulnerable to extirpation.” The BCCP Environmental Conservation Areas Map  [PDF] designates the St. Vrain Creek corridor as a Riparian Habitat Connector, which is an area of “wildlife movement adjacent to relative unfragmented waterways which provides connectivity among Environmental Conservation Areas.” Also informative are the BCCP Preble’s Meadow Jumping Mouse Conservation Areas Map [PDF] and the BCCP Wetlands & Riparian Areas Map [PDF]. In Best Management Practices for Wildlife Corridors, Beier et al. note that best practices for streams in corridors entail protecting or restoring a continuous strip of native vegetation at least 200 meters (656 ft) wide along each side of the channel.

The Survey of Critical Biological Resources in Boulder County, Colorado 2007-2008 [PDF] is an extensive report prepared for Boulder County by the Colorado Natural Heritage Program at Colorado State University. The “Saint Vrain Creek below Lyons” area is noted for its significant biodiversity. To address the problems posed by habitat fragmentation, the “Recommended Conservation Strategies” include recognizing the importance of larger, contiguous natural communities, to ensure that we do not lose species that have not yet been located (61).

Of course, the survey above precedes the 2013 flood. A more recent report created for Boulder County Parks and Open Space, the 2014 Riparian Inventory and Assessment of Post-Flood Conditions Boulder County Parks and Open Space Properties Boulder, Left Hand, and St. Vrain Creeks [PDF], claims that “Overall, flooding increased the potential for plant and animal diversity by creating new land forms, including new meanders and main channels, abandoned channels, side channels, point bars, and pools. Habitat for wetland plants in particular increased” (41). This underscores the need for an updated, post-flood survey of the entire area, which could reveal valuable new information about its current and potential biodiversity.

Bird studies

In 1997, two studies were conducted on birds in and around the property proposed for mining:

The report on breeding birds cites 60 species observed on the former Western Mobile, Inc. property, with 28 of those species definitely nesting on the property, 19 that may have nested, and 13 migrant or non-nesting summer visitants.

The report on birds of prey noted that bald eagles, red-tailed hawks, American kestrels, and great horned owls nest on the property where mining was initially proposed. In addition to potential nesting habitat for other raptors of special concern (golden eagle, northern harrier, and eastern screech owl), there is also potential foraging habitat on the property for at least five additional raptor species of special concern (golden eagle, ferruginous hawk, peregrine falcon, prairie falcon, and short-eared owl).

These 1997 reports are now two decades old. A new bird study is reportedly being conducted for Martin Marietta at this time, and S.O.S.V.V. community members look forward to reviewing and verifying the final bird study report(s).


At 562 species, Boulder County’s bee diversity is one of the highest in Colorado, and the St. Vrain Creek corridor provides important habitat for various kinds of pollinators. These species are key to the ecological balance in our region. As Kearns et al. note, “Loss of native bee species can lead to loss of native plants that rely on them for reproduction.” Riparian habitats are critical to the well-being of pollinators in the area, providing vital floral and nesting resources for a wide diversity of native bees. Dr. Adrian Carper is currently leading a team of researchers conducting a survey of native bees along the St. Vrain Creek corridor. They are studying the woody debris that bees require for their nesting habitat, and how its availability affects the abundance and diversity of cavity-nesting bees. As Dr. Carper stated in a recent presentation, “Open spaces are bee hotspots.” Let’s keep this important open space open.

Over the last two decades, the monarch butterfly population has declined by 90 percent. Monarchs pollinate many types of wildflowers as they feed on nectar. Milkweed—the only plant on which monarch butterflies lay eggs—can be found throughout the St. Vrain Valley. While Colorado falls between two of the main monarch migration paths, the region does host “strays,” and milkweed is necessary for their continuing survival.

Bald eagles

The Special Use permit issued two decades ago could allow gravel mining on 492 acres in the Saint Vrain Valley. The Hygiene Bald Eagle nest is located within the southern margin of the planned mine area, and gravel operations could be within close proximity of the nest. The nest tree and much of the land to be mined is owned by Boulder County (BCPOS), however, mineral rights are largely controlled by Martin-Marietta-Materials.

Similar to all known bald eagle nests in this part of the Front Range, the Hygiene nest hosts a prairie dog colony within close proximity.  This is arguably a prerequisite for the survival of these nests, especially during the more difficult winter months, as fish are often unavailable. This nearby source of prey is crucial, especially in winter, as it minimizes energy expenditure for these large nesting birds.

Gravel mining has the potential to destroy a significant portion of the adjacent prairie dog colony. The colony at the Hygiene nest extends nearly 0.5 miles into the fields north and east of the nest tree. The importance of these foraging fields has been recently documented during frequent monitoring sessions at the Hygiene nest during July and early August of 2017 (Dana Bove written communication). During this critical developmental period—post fledge and pre-fledgling migration– the two Hygiene eaglets spent as much as 53% of their time during each study session foraging in these fields (~0.25 miles north and east of the nest); the adult eagles also spent a large amount of time foraging there, spending up to 31% of their time budgets.

In the fledgling phase, prior to nest dispersal, the young eaglets are notoriously inept hunters, and depend on most of their food to be provided by the adults.  The opportunity for the fledglings to stalk and actually catch their own prey—as has been documented recently at the Hygiene nest—further demonstrates the importance of protecting the prairie dogs and the foraging fields where mining is planned.

Could the post-DDT recovery of bald eagle populations be bringing a a false sense of security and relaxed protections for nesting bald eagles in Boulder County and the Front Range? Please consider that here have been no new/successful Bald Eagle nests in Boulder County and adjacent Weld counties since 2014 (2 nests have moved due to disturbances). Boulder County Winter Raptor surveys show a resurgence of Bald Eagles in the early 1980’s, a peak in the early 90’s, and a decrease and mostly level population since that time ( On the other hand, growth, development, and habitat loss in the Front Range is sharply inclining. Due to their large size, nesting bald eagles require substantial-sized territories. Bald Eagle nests are still vulnerable, even on protected property. This is evident from current plans to mine at Hygiene nest; a plan to soon build 288 apartments ~600 ft from the Stearns Lake Bald Eagle nest (near the Holmberg preserve and on a protected conservation easement); and four other allowed eagle nest disturbances on Boulder County open space land since 2013.

All Boulder Conservation groups and concerned individuals need to speak out for protection of the Hygiene Bald Eagle nest. In your letters or calls to all applicable stakeholders in this issue, we ask that you insist that if mining is to occur, it is restricted to a minimum of 0.5 miles from the base of the nest tree.