Introduction and Range Expansion of Nonnative Red Foxes (Vulpes Vulpes) in California
Lewis, Jeffrey C., Sallee, Kevin L., Golightly, Richard T., Jr., The American Midland Naturalist
ABSTRACT: Predation on endangered species by nonnative red foxes (Vulpes vulpes) and the resulting controversy over red fox control efforts in California prompted our investigation of the introduction and range expansion of the red fox in California. Since the late1800s, nonnative red foxes have been introduced into California by escaping from fur farms and fox hunters, through intentional releases by pet owners and hrr-farm owners and translocations of previously introduced foxes. From 1990-1993 we conducted telephone interviews of wildlife professionals to obtain observations of nonnative red foxes outside the historical
range of the native Sierra Nevada red fox (V v. necator). Nonnative red foxes now occur throughout lowland areas of California including the Sacramento and San Joaquin valleys, San Francisco Bay-Delta area, the southern California Coast Range and Coastal Plain and most major urban areas. Their range expansion over the last 100 y was the result of population growth from numerous points of introduction and exhibited by the exponential growth typical of invading species. Fox predation on endangered species and opposition to red fox management have been the two largest management issues associated with this range expansion.
The red fox ( Vulpes vulpes) occupies one of the widest geographic ranges among carnivores (Lloyd, 1980). Introduction of red foxes by humans into previously unoccupied geographic regions (e.g., Australia in the mid 1800s; Saunders et al., 1995; Dickman, 1996) has been a major contributor to the expansion of its range. In the United States introductions of nonnative red foxes have occurred in the Eastern Seaboard (Presnall, 1958; Churcher, 1959), the Southeast (Lee et al., 1993), Alaska (Bailey, 1993), California (Grinnell et al., 1937), Idaho (Fichter and Williams, 1967), Oklahoma (Hatcher and Wigtil, 1985) and Oregon and Washington (Aubry, 1983). Fur farming and fox hunting in many of these areas resulted in the escape and release of foxes, and the establishment of nonnative red fox populations.
In California the native Sierra Nevada red fox ( Vulpes v. necator) occurred in high-elevation habitats of the Sierra Nevada and southern Cascade Range (Grinnell et al., 1937). Since the late-1800s however, nonnative red foxes have been found in areas of California outside the historical range of the Sierra Nevada red fox (Grinnell, 1933; Grinnell et al., 1937; Gray, 1975). Additional populations of nonnative red foxes were identified by wildlife managers in the early- to mid-1980s as a result of their predation upon the California clapper rail (Rallus longirostris obsoletus) in the San Francisco Bay Area, and upon the lightfooted clapper rail (R. l. levipes) and the California least tern (Sterna antillarum browni) in coastal southern California (U.S. Fish and Wildlife Service and U.S. Navy, 1990; U.S. Fish and Wildlife Service, 1990; Zembal, 1992). These endangered birds use ground nests, are restricted to coastal habitats and are particularly vulnerable to red fox predation (U.S. Fish and Wildlife Service and U.S. Navy, 1990; U.S. Fish and Wildlife Service, 1990; Zembal, 1992; Golightly et al., 1994).
Since nonnative red foxes pose a threat to several sensitive species, current information on their distribution and range expansion is critical to assess the magnitude of this threat and develop management recommendations to minimize impacts to native species. Our goal was to assess the distribution of nonnative red foxes in California and determine how this distribution may be changing. Our specific objectives were to: (1) summarize the history of introductions of nonnative red foxes in California, (2) describe the resulting range expansion, (3) identify factors that likely contributed to this expansion, (4) discuss the implications for native fauna and nonnative red fox management and (5) describe management options for nonnative red foxes. …