Habitat Loss and Alteration
Affecting the California Red-Legged Frog

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Fragmentation of the California Red-Legged Frog’s native habitat has been one of the most recognized causes for the decline in its population. Habitat fragmentation has been caused by urbanization of the surrounding areas of the Bay-Delta and especially in or nearby the native range of the California Red-Legged Frog.          Tidal wetlands and surrounding California Red-Legged Frog native habitat areas have slowly been filled in by Bay-Delta settlers and sediment from hydraulic mining done during the 1848 Gold Rush.          Prior to 1848 the Bay-Delta consisted of a massive amount of tidal wetlands. In addition to hydraulic mining by the Gold Rush settlers, the natural waterways were also dammed and diverted by State, Federal and local water projects Today only a fraction of the natural territory remains. Click to enlarge. The San Francisco Bay estuary and Delta at the time of the discovery of gold in the Sierra Nevada foothills (first panel) and at present (second panel)( Nichols, F.H. 2002). Click to enlarge. State, Federal and Local water projects.         Tadpoles are affected by habitat fragmentation because it leads to a smaller, more confined area in which the tadpoles have to survive. This leads to competition for food source. Habitat fragmentation and loss of habitat has also left less room for females to leave their egg masses.          As of 1960, the California Red-Legged Frog was extirpated from the Central Valley of California. Prior to 1960 the California Red-Legged Frogs were also once widespread and abundant in the inner Coast Ranges between the Salinas River system and the Central Valley. Rana aurora draytonii DISTRIBUTION MAP Department of Herpetology California Academy of Sciences Click Picture for Larger Version Historic and Current Distribution of Rana aurora draytonii in California based on 1205 museum records and 250 records from other sources. Jennings et al 1992         The combination of habitat alteration due to years of livestock grazing, agriculture, water use patterns, and recent 4-year drought are probably reason that recent records of the California Red-Legged Frogs are lacking for much of this region (61 Federal Register 25813). In the Central Valley of California over 90 percent of historic wetlands have been diked, drained or filled primarily for agricultural development and secondarily for urban development (U.S Fish and Wildlife Service 1978).