The San Joaquin kit fox has been listed as endangered for over 30 years, there has never been a comprehensive survey of its entire historical range. And, despite the loss of habitat and apparent decline in numbers since the early 1970s, there has been no new survey of habitat that was then thought to be occupied (Morrell 1975).
Despite the lack of a comprehensive survey, local surveys, research projects and incidental sightings indicate that kit foxes currently inhabit some areas of suitable habitat on the San Joaquin Valley floor and in the surrounding foothills of the coastal ranges, Sierra Nevada, and Tehachapi Mountains, from southern Kern County north to Contra Costa, Alameda, and San Joaquin Counties on the west, and near La Grange, Stanislaus County on the east side of the Valley (Williams in litt. 1990), and some of the larger scattered islands of natural land on the Valley floor in Kern, Tulare, Kings, Fresno, Madera, and Merced Counties. Kit foxes also occur westward into the interior coastal ranges in Monterey, San Benito, and Santa Clara Counties (Pajaro River watershed), in the Salinas River watershed, Monterey and San Luis Obispo Counties, and in the upper Cuyama River watershed in northern Ventura and Santa Barbara Counties and southeastern San Luis Obispo County. Kit foxes are also known to live within the city limits of the city of Bakersfield in Kern County (Laughrin 1970, Jensen 1972, Morrell 1975, USFWS 1983, Swick 1973, Waithman 1974a, Endangered Species Recovery Program unpubl. data).
Some researchers have suggested that as San Joaquin Valley natural lands were cultivated or otherwise developed, displaced kit foxes colonized nearby valleys and foothills (Laughrin 1970, Jensen 1972); however, there is no concrete evidence to support this assertion. As early as 1925, Grinnell et al. reported kit fox specimens from the Panoche Creek area in the foothills of western Fresno County, and east of Rose Station (Fort Tejon) in southern Kern County at an elevation of 363 meters (1,200 feet) (Grinnell et al. 1937, USFWS 1983). Therefore, it is more probable that kit foxes have always occurred in these areas, possibly at low density.
The largest extant populations of kit foxes are in western Kern County on and around the Elk Hills and Buena Vista Valley, Kern County, and in the Carrizo Plain Natural Area, San Luis Obispo County. The kit fox populations of Elk Hills and the City of Bakersfield, Kern County (B.L. Cypher pers. comm.), Carrizo Plain Natural Area, San Luis Obispo County (White and Ralls 1993, Ralls and White 1995), Ciervo-Panoche Natural Area, Fresno and San Benito Counties (Endangered Species Recovery Program), Fort Hunter Liggett, Monterey County (V. Getz pers. comm.), and Camp Roberts, Monterey and San Luis Obispo Counties (W Berry pers. comm.) have been recently, or are currently, the focus of various research projects. Though monitoring has not been continuous in the central and northern portions of the range, populations were recorded in the late 1980s at San Luis Reservoir, Merced County (Briden et al. 1987), North Grasslands and Kesterson National Wildlife Refuge area on the Valley floor, Merced County (Paveglio and Clifton 1988), and in the Los Vaqueros watershed, Contra Costa County in the early 1990s (V. Getz pers. comm.). Smaller populations and isolated sightings of kit foxes are also known from other parts of the San Joaquin Valley floor, including Madera County and eastern Stanislaus County (Williams 1990).
Diet of kit foxes varies geographically, seasonally, and annually, based on variation in abundance of potential prey. In the southern portion of their range, kangaroo rats, pocket mice, white-footed mice (Peromyscus spp.), and other nocturnal rodents comprise about one-third or more of their diets. Kit foxes there also prey on California ground squirrels, black-tailed hares, San Joaquin antelope squirrels, desert cottontails, ground-nesting birds, and insects (Scrivner et al. 1987a). Vegetation and insects occur frequently in feces. Grass is the most commonly ingested plant material (Morrell 1971, C.A. Vanderbilt-White pers. comm.). In the central portion of their geographic range, defined here as Kings, Tulare, Fresno, Madera, San Benito, Merced, Stanislaus, and Monterey Counties, known prey species include white-footed mice, insects, California ground squirrels, kangaroo rats, San Joaquin antelope squirrels, black-tailed hares, and chukar (Alectoris chukar) (Jensen 1972, Archon 1992), listed in approximate proportion of occurrence in fecal samples. In the northern part of their range, defined here as San Joaquin, Alameda and Contra Costa Counties, kit foxes most frequently consume California ground squirrels (Orloff et al. 1986). Cottontails, black-tailed hares, pocket mice, and kangaroo rats also are eaten (Hall 1983, D.F. Williams unpubl. data). Though ground squirrels are diurnal and kit foxes are predominantly nocturnal, kit foxes are commonly seen during the day during late spring and early summer (Orloff et al. 1986).
San Joaquin kit foxes use dens for temperature regulation, shelter from adverse environmental conditions, reproduction, and escape from predators. Though kit foxes are reputed to be poor diggers (Jensen 1972, Morrell 1972), the complexity and depth of their dens do not support this assessment (USFWS 1983). Kit foxes also modify and use dens constructed by other animals, such as ground squirrels, badgers, and coyotes (Jensen 1972, Morrell 1972, Hall 1983, Berry et al. 1987b), and human-made structures (culverts, abandoned pipelines, and banks in sumps or roadbeds) (Spiegel et al. in press, B.L. Cypher pers. comm.).
Den characteristics vary across the San Joaquin kit foxs geographic range. In the southernmost portion, dens with two entrances are most frequently found. Natal and pupping dens, in which pups are born and raised, tend to be larger with more entrances (2 to 18) (Morrell 1972, OFarrell and Gilbertson 1979, OFarrell et al. 1980, OFarrell and McCue 1981, Berry et al. 1987b). Entrances are usually from 20 to 25 centimeters (8 to 10 inches) in diameter and normally are higher than wide. Ramp-shaped mounds of dirt from 1 to 2 meters (3 to 6 feet) long are deposited at some den entrances (Morrell 1972). Most hillsides where kit fox dens are found (95 percent) have a slope of less than 40 degrees (Reese et al. 1992). Natal and pupping dens are found on flatter ground with slopes of about 6 degrees (OFarrell and McCue 1981, OFarrell et al. 1980). The entrances of pupping dens show more evidence of use, such as fox scat, prey remains, and matted vegetation. In the central portion of their geographic range, dens also have several openings; however, instead of a mound of dirt in front of the opening, the dirt is more often scattered into a long tailing ramp, generally with a runway down the middle. In areas of tall grass, matted grass in front of the entrance is obvious. In western Merced County, most dens are found on slopes of less than 10 degrees, but a few are found on slopes of up to 55 degrees (Archon 1992). In the northern portion of the kit fox range, dens appeared to be placed higher than most surrounding ground compared to areas farther south, perhaps reflecting the topography of the area. Dens most often are located on the lower section of the slope (Orloff et al. 1986), yet foxes are sometimes seen entering dens on the upper part of a slope (Bell 1992). Most dens lack the ramp or runway characteristic of dens in the southern and central portions of the Valley. No evidence has been found to indicate that kit foxes in this area construct their own dens (Hall 1983). Kit foxes probably enlarge California ground squirrel burrows (Orloff et al. 1986), but they also may construct their own dens.
Kit foxes often change dens and numerous dens may be used throughout the year. However, evidence that a den is in use may be absent (V. Getz pers. comm.). Reese et al (192) found that 64 percent of the dens used by radio-collared kit foxes at Camp Roberts during 1988-1991 exhibited no sign of kit foxes. Foxes change dens four or five times during the summer months, and change natal dens one or two times per month (Morrell 1972). One family of 7 kit foxes used 43 dens; the maximum number used by 1 individual was 70 (Hall 1983). Foxes on the Carrizo Plain Natural Area changed dens much more frequently than indicated by Morrells study (White and Ralls 1993). Radiotelemetry studies indicate that foxes use individual dens for a median of 2 days (mean of 3.5 days) before moving to a different den. One fox was tracked to 70 different dens during a two year study (K. Ralls pers. comm.). Den changes have been attributed to depletion of prey in the vicinity of the den or to increases in external parasites such as fleas (Egoscue 1956). Avoidance of coyotes is a more probable reason for frequently changing dens because kit foxes can easily search their home range in one night for prey, and parasites are unlikely to build to intolerable levels in 2 or 3 days (K. Ralls pers. comm.)
Nightly movements on the Elk Hills Naval Petroleum Reserves in California averaged 15.4 kilometers (9.6 miles) during the breeding season and were significantly longer than the average nightly movements of 10.2 kilometers (6.3 miles) during the pup-rearing season. Movements during the breeding season also were significantly longer than those made during the pup-dispersal season (10.4 kilometers, 6.5 miles) (Zoellick et al. 1987b).
Home ranges of from less than 2.6 square kilometers (1 square mile) up to approximately 31 square kilometers (12 square miles) have been reported by several researchers (Morrell 1972, Knapp 1978, Zoellick et al. 1987b, Spiegel and Bradbury 1992, White and Ralls 1993, Paveglio and Clifton 1988). The maintenance of large and relatively non-overlapping home ranges, as noted on the Carrizo Plain, may be an adaptation to drought-induced periods of prey scarcity that are episodic and temporary on the Carrizo Plain (White and Ralls 1993). Differences in home range size among study sites tend to be related to prey abundance (White and Ralls 1993, White and Garrott 1998).
Kit foxes are subject to predation or competitive exclusion by other species, such as the coyote, nonnative red foxes, domestic dog (Canis familiaris), bobcat (Felis rufus), and large raptors (Hall 1983, Berry et al. 1987a, OFarrell et al. 1987b, White et al. 1994, Ralls and White 1995, CDFG 1987). Coyotes are known to kill kit foxes, though an experimental coyote-control program at the Elk Hills Naval Petroleum Reserves in California did not result in an increase in survival rate for kit foxes, nor did coyote-induced mortality decrease (Cypher and Scrivner 1992, Scrivner and Harris 1986, Scrivner 1987). The extent to which gray and kit foxes compete for resources is unknown. The need for similar den sites and prey species probably place nonnative red foxes in direct competition with the much smaller kit fox. Nonnative red foxes are expanding their geographic range in central California (Orloff et al. 1986, Lewis et al. 1993), and competition with or predation on kit foxes may be a factor in the apparent decline of kit foxes in the Santa Clara Valley (T. Rado pers. comm.), and perhaps elsewhere in the northwestern segment of their range. Coyotes aggressively dominate encounters with red foxes and will pursue and kill both red and gray foxes (Sargeant and Allen 1989), as well as kit foxes. Coyotes may reduce the negative impacts of red foxes on kit foxes by limiting red fox abundance and distribution, but details of interactions between the two species and the extent to which coyotes might slow or prevent the invasion of red foxes into kit fox habitats are unknown (White et al. 1994, Ralls and White 1995).
San Joaquin kit foxes are primarily active at night (i.e., nocturnal), and active throughout the year (Grinnell et al. 1937, Morrell 1972). Adults and pups sometimes rest and play near the den entrance in the afternoons, but most above-ground activities begin near sunset and continue sporadically throughout the night. Morrel (1972) reported that hunting occurred only at night. Yet predation on ground squirrels, which are active during the day (i.e., diurnal), by some populations indicates that kit foxes are not strictly nocturnal, adapting to the activities of available prey (Balestreri 1981, Hall 1983, Orloff et al. 1986, OFarrell et al. 1987b, Hansen in litt. 1988).
Reasons for Decline.-- Numerous causes of kit fox mortality have been identified, though these have probably varied considerably in relative importance over time. Researchers since the early 1970s have implicated predation, starvation, flooding, disease, and drought as natural mortality factors. Shooting, trapping, poisoning, electrocution, road kills, and suffocation have been recognized as human-induced mortality factors (Grinnell et al. 1937, Morrell 1972, Egoscue 1975, Berry et al. 1987a, Ralls and White 1991, Ralls and White 1995, Standley et al. 1992).
y the 1950s the principal factors in the decline of the San Joaquin kit fox were loss, degradation, and fragmentation of habitats associated with agricultural, industrial, and urban developments in the San Joaquin Valley (Laughrin 1970, Jensen 1972, Morrell 1975, Knapp 1978). Extensive land conversions in the San Joaquin Valley began as early as the mid-1800s with the Arkansas Reclamation Act, and by 1958 an estimated 50 percent of the Valleys original natural communities had been lost (USFWS 1980a). In recent decades this rate of loss has accelerated rapidly with completion of the Central Valley Project and the State Water Project, which diverted and imported new water supplies for irrigated agriculture (USFWS in litt. 1995a). From 1959 to 1969 alone, an estimated 34 percent of natural lands were lost within the then-known kit fox range (Laughrin 1970). By 1979, only about 6.7 percent of the San Joaquin Valley floors original wildlands south of Stanislaus County remained untilled and undeveloped (USFWS 1980a). Such land conversions contribute to kit fox declines through displacement, direct and indirect mortalities, and reduction of prey populations.
Threats to Survival.-- Loss and degradation of habitat by agricultural and industrial developments and urbanization continue, decreasing carrying capacity of remaining habitat and threatening kit foxes. Livestock grazing is not thought to be detrimental to kit foxes (Morrell 1975, Orloff et al. 1986), but may alter the numbers of different prey species, depending on the intensity of the grazing. Livestock grazing may benefit kit foxes in some areas (Laughrin 1970, Balestreri 1981), but grazing that destroys shrub cover and reduces prey abundance may be detrimental (OFarrell et al. 1980, OFarrell and McCue 1981, USFWS 1983, Kato 1986).
Petroleum field development in the southern half of the San Joaquin Valley affects kit foxes by habitat loss due to grading and construction for roads, well pads, tank settings, pipelines, and settling ponds. Habitat degradation derives from increased noise, ground vibrations, venting of toxic and noxious gases, and release of petroleum products and waste waters. Traffic-related mortality is also a factor for kit foxes living in oil fields. The cumulative and long-term effects of these activities on kit fox populations are not fully known, but recent studies indicate that areas of moderate oil development may provide good habitat for kit foxes, as long as suitable mitigation policies are observed (OFarrell et al. 1980, Spiegel et al. in press). The impacts of oil activities at the Elk Hills Naval Petroleum Reserves in California on kit fox population density, reproduction, dispersal, and mortality appeared to be similar in developed and undeveloped areas of the Reserve (Berry et al. 1987a). The most significant impact on kit fox abundance in developed oil fields appears to be mediated through habitat loss. However, the relationship between habitat loss and population size in western Kern County is unclear: the Midway-Sunset oil field is highly developed with about 70 percent ground disturbance yet fox abundance is about 50 percent that of the undeveloped Lokern area (Spiegel et al. in press).
Other developments within the kit foxs range include cities and towns, aqueducts, irrigation canals, surface mining, road networks, non-petroleum industrial projects, power lines, and wind farms. These developments negatively impact kit fox habitat, but kit foxes may survive within or adjacent to them given adequate prey base and den sites. Kit foxes have been documented denning along canals and in levees (Jones and Stokes 1981, Hansen 1988), adjacent to highways (ESA Planning and Environmental Services 1986b, Hansen 1988), near wind farms (Hall 1983, Orloff et al. 1986), along power line corridors (Swick 1973), and at sanitary land fills (R. Faubion pers. comm.). Kit foxes also are known to live in and adjacent to towns such as Tulare (G. Presley pers comm.), Visalia (Zikratch pers. comm.), Porterville (Hansen 1988), Maricopa, Taft, and McKittrick (J.M. Sheppard pers. comm.) and the City of Bakersfield (Jones and Stokes 1981, B.L. Cypher pers. comm.). Bakersfieldfoxes (living in the Kern River Parkway) are reported to behave differently from animals in more remote populations: they often scavenge food from parking lots and dumpsters, have small foraging ranges, often are diurnal, and are relatively tame. This may be an expression of their ecological plasticity (e.g., Grinnell et al. 1937, p. 411, T. Murphy pers. comm., B.L. Cypher pers. comm.).
All these influences combine to compress and constrict the kit fox into fragmented areas, varying in size and habitat quality. The fragmentation of these areas coupled with the suspected high mortality during dispersal may limit movement to and habitat of these lands. As the human population of California continues to grow, the amount and quality of habitat suitable for kit foxes will inevitably decrease. Continued habitat fragmentation is a serious threat to the survival of kit fox populations.
The use of pesticides and rodenticides also pose threats to kit foxes. Pest control practices have impacted kit foxes in the past, either directly, secondarily, or indirectly by reducing prey. In 1925, near Buena Vista Lake, Kern County, seven kit foxes were found dead within a distance of 1 mile, having been killed by strychnine-poisoned baits put out for coyotes. It was suspected that hundreds of kit foxes were similarly destroyed in a single season (Grinnell et al. 1937). In 1975 in Contra Costa County (where the main prey item of kit foxes is the California ground squirrel), the ground squirrel was thought to have been eliminated county wide after extensive rodent eradication programs (Bell et al. 1994). In 1992, two kit foxes at Camp Roberts died as a result of secondary poisoning from rodenticides (Berry et al. 1992, Standley et al. 1992). The Federal government began controlling the use of rodenticides in 1972 with a ban of Compound 1080 on Federal lands pursuant to Executive Order. Above-ground application of strychnine within the geographic ranges of listed species was prohibited in 1988. Efforts have been underway to greatly reduce the risk of rodenticides to kit foxes (USFWS in litt. 1993).
Invasion and occupation of historical and potential kit fox habitats by nonnative red foxes may limit opportunities for kit foxes. Exclusion of kit foxes by competing red foxes, direct mortality, and potential for disease and parasite transmission all are issues that have not yet been researched. Therefore, we know neither the historical impacts to the kit fox, nor to what extent the continuing expansion of the range of nonnative red foxes will have on kit foxes.
Accidents and disease, though not well documented, are thought to play a minor role in kit fox mortality (USFWS 1983), however, at Camp Roberts rabies accounted for 6.3 percent of deaths of radio-collared kit foxes (Standley et al. 1992) and there is concern that rabies may be a contributing factor in the recent decline of kit foxes at Camp Roberts (P.J. White pers. comm.). Random catastrophic events such as drought or flooding present a significant threat. Drought, with a corresponding decline in prey availability, results in a decrease in kit fox reproductive success (White and Ralls 1993, Spiegel et al. in press). How extended periods of drought may affect kit fox populations is unclear, but local extinctions are likely in some isolated areas. Recently, small mammal populations have declined rapidly and severely, apparently due to the above average rainfall in the 1994-1995 precipitation year. In the Elk Hills region, relatively few pupping dens were found in 1995, and only a small proportion of kit fox pairs apparently raised pups (B.L. Cypher pers. comm., L.K. Spiegel pers. comm.).
The San Joaquin kit fox was listed as endangered by the U.S. Department of the Interior in 1967 (USFWS 1967) and by the State of California in 1971 (Table 1). A recovery plan approved in 1983 proposed interim objectives of halting the decline of the San Joaquin kit fox and increasing population sizes above 1981 levels (USFWS 1983).
Conservation efforts subsequent to the 1983 recovery plan have included habitat acquisition by USBLM, CDF, California Energy Commission, Bureau of Reclamation, USFWS, and The Nature Conservancy. Purchases most significant to conservation efforts were the acquisitions in the Carrizo Plain, Ciervo-Panoche Natural Area, and the Lokern Natural Area. A multi-agency acquisition is underway which would secure 60,000 acres straddling western Merced, Stanislaus, and eastern Santa Clara Counties. Other lands have been acquired as mitigation for land conversions, both temporary and permanent (Table 2). Mitigation in the form of management and research was granted to the California Energy Commission, U.S. Department of Energy (Naval Petroleum Reserves in California), Army National Guard (Camp Roberts), and Department of Defense (Fort Hunter Liggett). Most of the current research literature arises from these sources and The Smithsonian/Nature Conservancy-sponsored research on the Carrizo Plain Natural Area (White and Ralls 1993, White et al. 1994, Ralls and White 1995, White et al. 1996).
For over 15 years EG&G Energy Measurements has conducted research into the ecology of the kit fox population on the Naval Petroleum Reserves in California, Kern County. Reports have covered such topics as dispersal (Scrivner et al. 1987b), mortality (Berry et al. 1987a), and movements and home range (Zoellick et al. 1987b). Additionally, they have evaluated habitat enhancement, kit fox relocation, supplemental feeding (EG&G Energy Measurements 1992), and coyote control (Cypher and Scrivner 1992) as means of enhancing recovery. Other life history information has come from studies sponsored in whole or in part by CDFG, California Department of Water Resources, USFWS, Smithsonian Institution, Department of the Army and Air Force, California Energy Commission, and The Nature Conservancy (Hall 1983, Archon 1992, Spiegel and Bradbury 1992, White and Ralls 1993, White et al. 1994, 1996). Following the 1983 recovery plan, only three surveys for distribution have been conducted, two in the northern range of the fox (Orloff et al. 1986, Bell et al. 1994), and one in western Madera County (Williams 1990).
Large-scale habitat surveys have been conducted on the Carrizo Plain (Kato 1986, Kakiba-Russell et al. 1991) and the southern San Joaquin Valley (Anderson et al. 1991). A preliminary aerial survey for potential habitat was conducted along the east side of the Valley (Bell et al. 1994). There also have been numerous smaller-scale preproject surveys as part of the section 7 and 10(a) permit process of the Endangered Species Act, National Environmental Protection Act, and California Environmental Quality Act laws and regulations.
A population viability analysis was prepared for USFWS using RAMAS/a, a Monte Carlo simulation of the dynamics of age-structured populations (Buechner 1989). Since this analysis, deficiencies in the database have been identified and a metapopulation analysis has been completed (Kelly et al. 1995). This analysis, however, is preliminary and will be updated as new information is collected.
The U.S. Environmental Protection Agency County Bulletins governing use of rodenticides have greatly reduced the risk of direct mortality to San Joaquin kit fox populations by State and county rodent-control activities. The California Environmental Protection Agency, California Department of Food and Agriculture, county agricultural departments, CDFG, and U.S. Environmental Protection Agency collaborated with the USFWS in the development of County Bulletins that are both efficacious and acceptable to land owners (R.A. Marovich pers. comm.).
Source: Endangered Species Recovery Program