"We should have been seeing vesper sparrows, grasshopper sparrows, the specialized species of conservation interest," says ecologist Buffy Lenth, the study's lead author. Instead, she and her coworkers saw starlings, grackles and robins, the same old generalist species and invasives that characterize the fragmented habitat of traditional development. The reason was not entirely clear. Lenth suspected heavy use of the open space by residents and their pets might be a factor, along with its small size and a design intended to maximize views rather than conservation.

All of these issues contribute to a growing sense that clustered development is not living up to its promise. "I've watched the Land Preservation Subdivision program as it was developed and used over the years, and from a habitat preservation standpoint, it's not great," says Jim Haskins, wildlife manager with the Colorado Parks and Wildlife Steamboat Springs office in Routt County.

Marabou Ranch, one of the newest and most upscale LPS developments in Routt County, offers hints as to where the problems might lie. The 1,717-acre subdivision five miles west of Steamboat Springs fulfills Routt County's guidelines to the letter and circumvents many, but not all, of the issues identified by Reed. It has reserved 1,325 acres as open space; a lot map in the sales office marks the location of a lek site for Columbian sharp-tailed grouse and an elk-calving area, both of which are off-limits to development and subject to seasonal closure. A resident manager is responsible for stewardship. But 62 homesites are scattered throughout the site; the open space, though large, is fragmented, with lots of edges. The sensitive habitat is located at the edges of the property; the lek lies along the road and the calving area is crowded by homesites.

Carbonell tends to blame the way such developments are originally planned. "It's important (for planners and developers) to start interacting before a design gets finalized. In the absence of understanding how watersheds work, or how an ecosystem works, you can get development patterns that are not terribly functional."

Not surprisingly, the projects that have done well on an ecosystem scale are enormous, built by developers with deep pockets and a grand vision. Santa Lucia Preserve, Calif., is 20,000 acres, with 18,000 acres permanently conserved. Galisteo Basin Preserve outside of Santa Fe, N.M., is 13,522 acres, with more than 12,800 acres of open space. Highlands Ranch, Colo., is 22,000 acres with 13,000 acres preserved, including a "backcountry wilderness" of 8,200 acres that supports an elk herd.

These three developments preserve meaningful chunks of open land and connect with other natural reserves -- conservation easements, state parks, national forest. They also take habitat stewardship seriously. The Santa Lucia Preserve established an endowment to fund the Santa Lucia Conservancy, a nonprofit group with an independent board, to manage its preserve land and set long-term ecological goals. The Galisteo Basin Preserve coordinates with two nonprofit organizations, a corps of graduate students, and local volunteers to perform monitoring and restoration work. Highlands Ranch employs three full-time natural area managers and seasonal rangers, plus resident volunteers.

However, it is possible to achieve landscape-level results through interaction and flexibility. Just west of Salt Lake City, Utah's Tooele County specifically requires that at least 75 percent of a development's open space lots "shall be in a contiguous tract" and "adjoin any neighboring areas of open space." Douglas County, Colo., is currently amending its regulations to mandate formal community meetings before a project is finalized. Then the development can better meet the conservation goals articulated in the community's master plan: Wildlife corridors and open-space parcels can be planned so that they align, watersheds can be protected along their length,  and development can be steered so that it clusters along major roadways and population centers.

"Watersheds, ecosystems, migration patterns can be functional in close proximity to people and cities," says Carbonell. Conservation development is just another element in the planning process. Reed recommends that the open-space parcels be big enough (she is currently seeking funding to determine the best size), and that they minimize edges and be properly monitored and maintained. The entire project should be surveyed at the start to identify critical habitat, and the development should be planned around it. Finally, the open-space parcels should communicate with other natural areas outside of the development.

Ideally, Reed says, each community should develop a vision that manages growth while protecting critical areas and corridors for biodiversity -- and then use "conservation development as one way to attain that ideal configuration."