Problems can also arise like in the case of the tangled ecology of San Francisco Bay who also tripped as ecological restorers. In the mid-twentieth century, engineers drained many of the bay's marshes and mud banks for building projects. But attitudes changed. Conservationists became concerned about the loss of natural habitat, and from the 1970s, engineers spent more millions of dollars on plugging up their drains to restore lost mudflats, salt marshes, and other wetlands. As part of this program, the Army Corps of Engineers began planting rewetted marshes with a cordgrass native to the eastern United States Spartina alterniflora. This new grass began to interbreed with its close relative, the local California cordgrass (Spartina foliosa). The result was a new hybrid grass that colonized much more aggressively than either of its forebears. It spread to areas no one had intended, blanketing previously open mudflats, clogging channels, getting in the way of oyster farmers, and—worst of all, for many—spoiling million-dollar views and damaging the value of upscale waterfront properties. So a decade ago, authorities launched a multimillion-dollar project to rid the bay of both the alien from the east and the hybrid. But that went wrong too. It turned out that one of the bay's most totemic and endangered birds, the chicken-sized and largely flightless California clapper rail (Rallus longirostris obsoletus), had grown partial to the new hybrid grass. The grass grew more densely than the local version and didn't die back during the winter, providing better cover and nesting habitat for the secretive bird. During the 1990s, as the hybrid spread, the rail population had soared. But after 2004, as the eradication got underway, the bird's numbers crashed. There was no mistaking the cause. In time and space, the bird population declined following the eradication of the alien grass.