Like the riparian zones, native grassland and shrublands have been heavily impacted by invasive species. A 2009 survey conducted in the Aliso Creek watershed found non-native grass coverage of between 66 and 100 percent, and non-native shrub coverage of between 0 and 50 percent, across fourteen sample sites. Animals Mountain lions, bobcats, mule deer, gray fox and other large mammals once ranged throughout the Aliso Creek watershed; today, they are mostly confined to the wilderness reserves in the Santa Ana Mountains (Cleveland National Forest) and San Joaquin Hills (Aliso/Wood Canyons, Laguna Coast Wilderness). Most large mammal populations in the Aliso/Wood Canyons area are considered at risk of extirpation by the 2040s, in the absence of extensive habitat restoration. Mountain lions have already disappeared from Aliso/Wood Canyons. Although most of the creek channel is tightly bound by urban development, it is considered a potential wildlife corridor between these two areas. The U.S. Army Corps of Engineers describes the corridor as "meager at best with several places where Aliso Creek is very narrow, concrete, or incorporates golf courses parks and school grounds." The watershed supports multiple native bird species, including California least tern, least Bell's vireo, southwestern willow flycatcher, California gnatcatcher, and western snowy plover. The loss of riparian zones has reduced bird habitat in the watershed. These species are mostly found in undeveloped areas of Aliso and Wood Canyons, the upper reaches of Aliso Creek, and some parts of English Canyon Creek. Aliso Canyon is one of the most diverse bird habitats in Orange County, with some 122 nesting and migratory species found there. The canyon also has raptors including northern harrier, Cooper's hawk, golden eagle and peregrine falcon. The creek has several species of amphibians and reptiles. Species of concern listed by the state of California include the Coastal Range newt, orange-throated whiptail, coastal western whiptail, coast horned lizard, California legless lizard, and two-striped garter snake. Native frogs and the arroyo toad once inhabited the creek, but they were extirpated by damage to the channel following floods in 1983. Non-native bullfrogs have been introduced to parts of the creek. The threatened southwestern pond turtle, the only indigenous turtle species to Orange County, is also found in the creek. Fish and amphibians Although many fish species were once found in Aliso Creek, the only remaining one is the introduced common carp, which can tolerate the low oxygen levels and high temperatures