Endangered Species Recovery Program

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Recovery Plan for Upland Species of the San Joaquin Valley, California
Contents . Introduction . Species accounts . Recovery . Stepdown . Implementation . References . Appendix

I. Fresno Kangaroo Rat (Dipodomys nitratoides exilis)

1. Description and Taxonomy

Taxonomy.-- The Fresno kangaroo rat is one of three subspecies of the San Joaquin kangaroo rat. The type specimen of the Fresno kangaroo rat was collected from Fresno, California, in 1891. Merriam (1894) considered the Fresno and the Tipton kangaroo rats to be subspecies of Merriams kangaroo rat (Dipodomys merriami), a widespread species occurring in the Mojave Desert of California and elsewhere in western North America. Yet, Grinnell (1921) noted that the populations of "D. merriami" from the San Joaquin Valley were distinct from other members of this species. Grinnell (1922) subsequently reclassified exilis as a subspecies of a new species, the San Joaquin kangaroo rat (D. nitratoides). Fresno and Tipton kangaroo rats are similar in overall structure and occupy contiguous geographic ranges on the floor of the Tulare Basin and southeastern half of the San Joaquin Basin in the San Joaquin Valley. A third subspecies, the short-nosed kangaroo rat, is found in the foothills and basins along the western side of the San Joaquin Valley south of Los Banos, Merced County on the north, and western portions of the Tulare Basin, the upper Cuyama Valley, and Carrizo Plain (Williams et al. 1993a).

Boolootian (1954) studied structural variation in populations of D. nitratoides, concluding that exilis did not merit recognition as a subspecies and regarded it to be a synonym of nitratoides. Hall and Kelson (1959) did not follow Boolootians (1954) recommendation for reasons they attributed to the unpublished advice of Seth Benson (former Curator of Mammals, niv. California, Berkeley, Museum of Vertebrate Zoology). In a masters thesis study of Fresno kangaroo rats, Hoffmann (1975) concluded that Benson erred in his determination of the identity of some San Joaquin kangaroo rats, but that exilis was identifiable as a subspecies. Williams (1985) agreed with Hoffmanns conclusions that the samples he regarded as exilis were distinguishable from those he had available of nitratoides and brevinasus, but noted that the subspecies were practically indistinguishable when samples of populations from localities intermediate to the geographic locations of Hoffmanns samples of exilis and nitratoides were included. DNA studies to resolve this issue are currently being conducted. Investigators using serum proteins (Johnson and Selander 1971, Patton et al. 1976, Best and Janecek 1992) and chromosome structure (Stock 1971, Patton et al. 1976) found substantial differences at the species level between D. nitratoides and D. merriami, supporting Grinnells (1922) earlier species reclassification. Subspecies taxonomy of D. nitratoides was most recently reviewed by Williams et al. (1993a) and all were retained.

Description.-- The San Joaquin kangaroo rat is similar in general appearance to the other 20 species of kangaroo rats, but is smaller, and differs substantially from all other species in several ways (Figure 42). Like all kangaroo rats, the San Joaquin kangaroo rat is adapted for survival in an arid environment. Adaptations for bipedal locomotion include elongated hind limbs, a long, tufted tail for balance, a shortened neck, and, compared to typical rodents, a large head. The skull is flattened from top to bottom, with enlarged auditory bullae (bony capsules containing the middle and inner ears). Other characteristics include large eyes placed near the top of the head and small, rounded ears. Forelimbs are comparatively short with stout claws that facilitate digging burrows (Best 1991). Its total length averages about 231 millimeters (9.09 inches) for males and 225 millimeters (8.86 inches) for females (Hoffmann 1975). The hind foot usually is less than 36 millimeters (1.42 inches) in length. The fur is dark yellowish-buff dorsally and white ventrally (Knapp 1975). A white stripe extends across the hips, continuing for the length of the prominently tufted tail. The base of the tail is circumscribed by white. Dorsal and ventral sides of the tail are blackish. Dark whisker patches on each side of the nose are connected by a black band of fur (Grinnell 1922, Culbertson 1934, Williams 1985).

Identification.-- The San Joaquin kangaroo rat can be distinguished from other kangaroo rats within its geographic range by the presence of four toes on the hind foot; the other species found in the same area have five toes. The Fresno kangaroo rat is the smallest of the three subspecies of D. nitratoides. Individuals of the three subspecies of D. nitratoides cannot be reliably distinguished without dissection unless the geographic origin of the individual is known. The Fresno kangaroo rat is distinguished from the other subspecies of the San Joaquin kangaroo rat by its smaller average measurements (in millimeters): length of hind foot for males 33.9 millimeters (1.33 inches), for females, 33.4 millimeters (1.31 inches); mean inflation of the auditory bullae for males, 21.4 millimeters (0.84 inch), for females, 21.2 millimeters (0.83 inch) (Hoffmann 1975) (see accounts of Tipton and short-nosed subspecies for corresponding average measurements).

Figure 42
Figure 42. Illustration of a San Joaquin kangaroo rat (Dipodomys nitratoides) by Jodi Sears based on photo © by D.F. Williams.

2. Historical and Current Distribution

Historical Distribution.-- The known historical geographic range of the Fresno kangaroo rat encompassed an area of grassland and chenopod scrub communities on the San Joaquin Valley floor, from about the Merced River, Merced County, on the north, to the northern edge of the marshes surrounding Tulare Lake, Kings County, on the south, and extending from the edge of the Valley floor near Livingston, Madera, Fresno, and Selma, westward to the wetlands of Fresno Slough and the San Joaquin River (Figure 43). Documentation of historical distribution is scanty. Boolootian (1954), Culbertson (1934, 1946), Hoffman and Chesemore (1982), Hoffmann (1974, 1975), Knapp (1975), Williams (1985), and Williams et al. (1993a) collectively provided a composite picture of the historical distribution and documentation of the loss and fragmentation of habitat. An estimate of the historical range, within the area as outlined above, is approximately 359,700 hectares (888,500 acres; Williams 1987). Not all this area would have been habitat for Fresno kangaroo rats.

Current Distribution.-- There are no known populations within the circumscribed historical geographic range in Merced, Madera, and Fresno Counties. A single male Fresno kangaroo rat was captured twice in autumn 1992 on the Alkali Sink Ecological Reserve, west of Fresno. Trapping at the Reserve in 1993, 1994, and 1995 did not yield additional captures. Fresno kangaroo rats were previously trapped on the Alkali Sink Ecological Reserve in 1981 and 1985, and on adjacent privately owned land in 1981 (Hoffman and Chesemore 1982, Chesemore and Rhodehamel 1992). Though the Alkali Sink Ecological Reserve is now about 382.4 hectares (945 acres), suitable habitat there for Fresno kangaroo rats probably totals about 162 hectares (400 acres). Trapping at other sites in Merced, Madera, and Fresno Counties between 1988 and 1995 failed to locate other, extant populations within the area typically considered as the geographic range of the Fresno kangaroo rat (Chesemore and Rhodehamel 1992, Williams and Kilburn 1992, D.F. Williams unpubl. data).

Figure 43
Figure 43. Distributional records for the Fresno kangaroo rat (Dipodomys nitratoides exilis)

Other areas of west-central Fresno County that were inhabited historically by Fresno kangaroo rats, and that were uncultivated in 1981, included nine separate sites. Two of the nine parcels now are partly cultivated but 715.7 hectares (1,768.4 acres) in two others were purchased by the State (now the Kerman Ecological Reserve). Fresno kangaroo rats have not been found at any of these sites during surveys between 1988 and 1996 (Endangered Species Recovery Program unpubl. data).

Populations of San Joaquin kangaroo rats have been found on about 150 hectares (371 acres) comprising five isolated parcels in Kings County, south of the historical river and slough channels of the Kings River and north of the Tulare Lake bed (Williams 1985, D.F. Williams unpubl. data). Staff of the Endangered Species Recovery Program last verified occurrence of two populations in 1994 and 1995. One site, 39 hectares (97 acres) in size, is located on Lemoore Naval Air Station. Whether these populations belong to the Fresno or Tipton subspecies is uncertain, but historically, they were geographically contiguous and probably periodically connected to populations identified as Fresno kangaroo rats. Genetic and morphometric studies (to measure the size of the feet and auditory bullae) of these populations are in progress (J.L. Patton pers. comm.).

Other areas with possibly extant populations of Fresno kangaroo rats include uncultivated grassland, alkali sink shrubland, and seasonally flooded wetlands within the historical range of the species, in Fresno, Madera, and Merced Counties. Trapping at selected sites in all three counties between 1988 and 1995 has failed to confirm presence, but lack of permission to trap on private lands has prevented a thorough search by staff of the Endangered Species Recovery Program. Populations of D. nitratoides occurred on the Mendota Wildlife Area, Fresno County, both east and west of the Fresno Slough, but the population west of Fresno Slough was regarded by Hoffmann (1975) as representing D. n. brevinasus rather than exilis, though they were intermediate to the two subspecies structurally (Boolootian 1954). Occurrence on the Wildlife Area has not been verified, despite trapping in 1981 and 1993.

San Joaquin kangaroo rats also have been taken recently in seasonally-flooded iodine bush (Allenrolfea occidentalis) shrublands in the South Grasslands Water District, Merced County. This population is located in an area historically considered part of the geographic range of the shot-nosed subspecies. Individuals exhibit structural characteristics somewhat intermediate to brevinasus and exilis, but are found in the same habitat as exilis and have been tentatively assigned to exilis (Johnson and Clifton 1992, Williams et al. 1993a). These areas are privately owned lands included in the wetland waterfowl easement program of USFWS.

3. Life History and Habitat

Food and Foraging.-- Fresno kangaroo rats collect and carry seeds in fur-lined cheek pouches. Seeds are a staple in their diet, but they also eat some types of green, herbaceous vegetation, and insects. A wide variety of seeds probably are consumed, depending on availability. Known foods include seeds of annual and perennial grasses, particularly wild oats, brome grasses (red and ripgut [B. diandrus] brome, soft chess [B. hordeaceus]), wild barley (Hordeum sp.), mouse-tail fescue, alkali sacaton, and saltgrass; and seeds of annual forbs such as filaree, peppergrass, common spikeweed (Hemizonia pungens), and shepherds purse (Capsella bursa-pastoris) (Culbertson 1946, Koos 1979). Seeds of the woody and semiwoody shrubs, iodine bush and seepweed (Sueda moquinii), also are eaten (Koos 1979). Seeds of woody shrubs, especially saltbushes are diligently sought out by Tipton and short-nosed kangaroo rats, and also probably are important for Fresno kangaroo rats (D.F. Williams unpubl. observ.). Insects make up a small part of the diet, varying from about 2 to 10 percent frequency in fecal samples (Koos 1979).

Most kangaroo rats gather seeds when they are available and cache them for consumption later. Typically, caches are made in small pits that hold the contents of the two cheek pouches. Caches are located on the surface of the soil, and are typically scattered over the home range of the individual. A few, small, seed caches were found in excavated burrows of Fresno kangaroo rats (Culbertson 1946). These small caches also hold only about the contents of two cheek pouches. Culbertson (1946) speculated that Fresno kangaroo rats did not cache seeds in their burrows to the same extent as other kangaroo rats because the soil where they lived was damp much of the year. Seeds would spoil rapidly under such conditions. He also speculated that Fresno kangaroo rats therefore were obligated to forage on the surface year round to a greater extent than kangaroo rats that cached more food. In fall and winter, after the wet season commences, sprouts of seeds and tender new growth of grasses and forbs may be essential items in the diet of Fresno kangaroo rats. Green developing seed heads may be important in the spring months. Seeds, and perhaps insects, are the most important items in the diet in late spring, summer, and fall.

Reproduction and Demography.-- Nothing is known about mating behavior or the mating system of Fresno kangaroo rats in the wild. Culbertson (1946) recorded observations of captive Fresno kangaroo rats, including young born in captivity, and Eisenberg (1963) and Eisenberg and Issac (1963) described mating behavior and care of young in a captive colony of short-nosed kangaroo rats. Mating probably takes place on the surface within the territory of the female. Culbertson (1946) did not locate nests in excavated burrow systems and wrote that captive, pregnant females usually did not make nests before giving birth. He thought that this was because they were greatly disturbed by capture and confinement shortly before giving birth.

Sexual maturity was attained in as little as 82 days after birth. Pregnant female Fresno kangaroo rats have been taken between February and March and June and September (Hoffmann 1974). Pregnancies between June and September might represent second or third litters for adult females, summer breeding by young females born in the spring, or both. Females are probably capable of breeding two or more times per year.

Breeding probably is initiated in winter after onset of the rainy season. Nothing is known about pair bonds in wild populaions, but there probably are no lasting male-female pair bonds formed. Females may breed with more than one male during a breeding cycle, though typically a single male attains dominance for mating purposes with one or more females within his territory, as is true of closely related kangaroo rat species. Most females born the previous season probably do not give birth until mid-February or early March during years with average or below average rainfall. In captivity, gestation was 32 days and young were weaned at 21 to 24 days. Average litter size in captive Fresno kangaroo rats was about two (range, one to three) (Culbertson 1946, Eisenberg and Issac 1963).

Young are born in the burrow, probably within a nest of dried, shredded vegetation. Young remain continuously in the burrow until they are fully furred and able to move about easily. Culbertson (1946) believed that young Fresno kangaroo rats were not found out of the burrow and foraging for themselves until about 6 weeks old. This is consistent for estimates for Tipton and short-nosed kangaroo rats (D.F. Williams, unpubl. data).

Based on limited information, populations of Fresno kangaroo rats probably turn over annually with most individuals born in the spring or summer not surviving to breed the following spring (Hoffmann 1974, Williams et al. 1993b, D.F. Williams unpubl. data). In the only study of Fresno kangaroo rats, Hoffmann (1974) found that only 2 of 75 marked animals were present on study plots through four trapping periods between 10 February and 28 December. Numbers were lowest in April, prior to dispersal of spring-born young, and peaked in May. By June, juveniles comprised the majority of the population. Maximum longevity in natural populations is probably between 3 to 5 years, based on studies of short-nosed kangaroo rats (Williams et al. 1993b).

Reproductive potential of Fresno kangaroo rats is relatively low compared to most rodents. Limiting factors on populations are unknown, but availability of suitable sites for burrows, free from winter flooding, probably is a major factor. No specific information is available on limitations of food. Likewise, there is no information on the roles of disease and predation in the population dynamics of Fresno kangaroo rats. Under current conditions of small, isolated and potentially inbred populations, both disease and predation are major threats.

Home range size varies by habitat features, season, and sex. Warner (1976) found home ranges to be small overall at an average of about 566 square meters (677 square yards) at the Alkali Sink Ecological Reserve. Warners data may underestimate the typical home range size based on reports of other kangaroo rats. For example, in the closely related species, D. merriami, size of home range averaged about 1.65 hectares (16,500 square meters, 4.06 acres) for males and 1.57 hectares (15,780 square meters, 3.9 acres) for females in a study in New Mexico (Blair 1943).

In one study, estimates of population densities varied from about 16.7 to 24.8 Fresno kangaroo rats per hectare (6.8 to 10.1 per acre) during a period from February through December (Hoffmann 1974). Other studies estimated densities from 2 to 29.3 Fresno kangaroo rats per hectare (0.8 to 11.9 per acre) at different sites and in different seasons (Warner 1976, Koos 1977, 1979). Hoffmann (1974) believed that competition with Heermanns kangaroo rat, a larger, more widely-distributed species that uses a broader range of plant communities, might be an important factor in elimination of Fresno kangaroo rats from sites impacted heavily by grazing.

Behavior and Species Interactions.-- Fresno kangaroo rats shelter in ground burrows that are dug by them or their predecessors. Burrows usually are found in relatively light, crumbly soils in raised areas. The surface area covered by the burrow system of individual Fresno kangaroo rats generally varies from about 2.1 to 3.7 meters (7 to 12 feet) on a side. There are usually two to five burrow entrances that slant gently underground, and one or more holes that open from a vertical shaft. Tunnels are about 51 millimeters(2 inches) in diameter and extend about 30.5 to 38.1 centimeters (12 to 15 inches) below ground. There may be several interconnecting tunnels and numerous dead-end side branches. Nesting material or large food caches have not been found in the few burrows that have been excavated (Culbertson 1946).

The burrow system is the apparent focus of territoriality in San Joaquin kangaroo rats. Except for young associated with females, each burrow system is typically occupied by a single individual. Culbertson (1946) found that captive Fresno kangaroo rats always fought when placed together in a small cage, and concluded that individuals were intolerant of each other. Yet when given sufficient space, individuals in a captive breeding colony of short-nosed kangaroo rats were more tolerant of others than expected from the typical behaviors of other species (Eisenberg 1963, Eisenberg and Isaac 1963). The social relations of Fresno kangaroo rats in the wild are unknown.

Activity Cycles.-- Fresno kangaroo rats are nocturnal and active year round. They do not hibernate and cannot recover unaided from hypothermia. Tappe (1941) reported seeing Tipton kangaroo rats emerge from their burrows and begin above-ground activities as early as seven minutes before sunset in early spring. Other kangaroo rats in the San Joaquin Valley are sometimes seen above ground by day in March and April (D.F. Williams unpubl. observ.), but this is considered to be rare and isolated deviations from the typical nocturnal activity. In one study, the peak period of capture of Fresno kangaroo rats occurred later after dark than that of the larger, more aggressive Heermanns kangaroo rats (Hoffman 1985).

Habitat and Community Associations.-- Fresno kangaroo rats occupy sands and saline sandy soils in chenopod scrub and annual grassland communities on the Valley floor. Recently they have been found only in alkali sink communities between 61 to 91 meters (200 to 300 feet) in elevation. Topography is often nearly level, consisting of bare alkaline clay-based soils subject to seasonal inundation and are broken by slightly rising mounds of more crumbly soils, which often accumulate around shrubs or grasses. Associated plant species include seepweed, iodine bush, saltbushes, peppergrass, filaree, wild oats, and mouse-tail fescue (Culbertson 1946, Hoffmann 1974, Hoffman and Chesemore 1982).

Within the alkali-sink plant associations, Fresno kangaroo rats probably were the most numerous small mammal under natural conditions, based on observations of the D. nitratoides population in an alkali sink community in the South Grasslands area of Merced County (Endangered Species Recovery Program unpubl. observ.). As such, they were a keystone species, providing a major source of food for a variety of predators, including the endangered San Joaquin kit fox. Their burrows were used extensively by the endangered blunt-nosed leopard lizard and other reptiles (Culbertson 1946, Williams 1985). Their seed-caching behaviors may have been important in the dispersal and germination of some plants, and their burrowing and digging probably beneficially affected soil structure and fertility (Williams 1985).

4. Reasons for Decline and Threats to Survival

Reasons for Decline.-- When the Fresno kangaroo rat was discovered in 1891, cultivation of its habitat already was threatening the species existence (Merriam 1894). By the early 1900s, it was believed to be extinct (Grinnell 1920), only to be rediscovered in 1933 (Culbertson 1934). By 1974, known habitat for these animals had been reduced and fragmented into three major areas, encompassing approximately 5,920 hectares (14,629 acres) in Fresno County, primarily by agricultural developments, urbanization, and transportation infrastructures (Knapp 1975). With the exception of the Alkali Sink Ecological Reserve and adjacent private land, Hoffman and Chesemore (1982) reported that only 2,396 hectares (5,920 acres) of potentially suitable habitat remained in Fresno County. Of this total, they considered 2,072 hectares (5,120 acres) to be margnal because of heavy livestock grazing. Actual presence of Fresno kangaroo rats was not confirmed on any of the nine isolated parcels composing this total.

Threats to Survival.-- In spring of 1986 a levee on the south side of the San Joaquin River broke, flooding the Alkali Sink Ecological Reserve and other important habitat. Water nearly a meter deep covered most of the area for several days.

The Alkali Sink and Kerman Ecological Reserves have not been actively managed since they were purchased as habitat for Fresno kangaroo rats and other species of the Alkali Sink communities. Livestock grazing that occurred prior to acquisition by CDFG was suspended after purchase, and some parcels now have heavy growths of herbaceous plants and deep mulch cover. The change in land use from grazing to no grazing may have been a factor in the apparent elimination and possible extinction of the Fresno kangaroo rats at the Alkali Sink Ecological Reserve. Yet, conclusive data on effects of livestock grazing on habitat quality for Fresno kangaroo rats is lacking. It is likely that seasonal grazing at levels considered good range-management have a beneficial effect on habitat quality for D. nitratoides.

Loss of habitat to cultivation, year-round grazing (which typically requires supplemental feeding), and conversion of land to other uses continue to diminish the size and quality of extant, historical habitat. Coupled with the resulting fragmentation and isolation of habitat, these developments increase the probability of extinction. Flooding poses a high risk to protected habitat in Fresno County because of its proximity to the San Joaquin River and because this land is the same or only slightly higher in elevation than the riverbed. If a population of Fresno kangaroo rats still is extant in the area, another break in the river levee could cause its extinction. Other potential threats are the illegal use of rodenticides, competition with Heermanns kangaroo rats, and disease and predation, any of which could eliminate small, isolated populations (Williams and Germano 1993).

5. Conservation Efforts

The Fresno kangaroo rat was listed by the State of California as Rare on June 27, 1971 (Title 14, Calif. Admin. Code, Sec. 670.5). It was subsequently changed by the State to Endangered status on October 2, 1980 (Title 14, Calif. Admin. Code, Sec. 670.5). The Fresno kangaroo rat was designated as a federally-listed endangered species on 30 January 1985 (Table 1; USFWS 1985b).

Accompanying the listing of the Fresno kangaroo rat as endangered was the designation of 347 hectares (857 acres) as critical habitat. In 1985, when it was designated as critical habitat, 9.3 hectares (23 acres) were a small part of the 4,343-hectare (10,732-acre) Mendota Wildlife Area, and 296 hectares (732 acres) comprised the contiguous Alkali Sink Ecological Reserve, both State-owned and managed. The remaining 41.3 hectares (102 acres) of critical habitat were in five privately-owned parcels (Figure 44). Critical habitat is defined as specific areas within and outside the geographic area occupied by a species at the time of Federal listing on which are found those physical or biological features (I) essential to the conservation of the species and (II) which may require special management considerations or protection.

Figure 44
Figure 44. Designated critical habitat for the Fresno kangaroo rat

Concern centering around the continued loss of extant natural communities within the geographic range of the Fresno kangaroo rat precipitated State listing and subsequent studies on the life history, distribution, and threats to remaining populations (Hoffmann 1974, Knapp 1975, Koos 1977, Hoffmann and Chesemore 1982). The State Wildlife Conservation Board began acquiring habitat in 1978 in the vicinity of Whitesbridge Road (Fresno County) for establishment of the Alkali Sink Ecological Reserve. The primary purpose of these acquisitions was protection of State-listed species and alkali sink communities. Between 1978 and 1985, the State purchased approximately 377 hectares (931.7 acres) at a cost of about $1.32 million (J. Gustafson pers. comm.). Another 1.3 hctares (3.3 acres) of previously cultivated land were added later to the Alkali Sink Ecological Reserve, making its current size 382.4 hectares (945 acres). Acquisitions to date include approximately 85 percent of the designated 347 hectares (857 acres) of critical habitat for the Fresno kangaroo rat. Remaining critical habitat outside of the Alkali Sink Ecological Reserve encompasses approximately 16.2 hectares (40 acres) in three separate parcels under private ownership in NE 1/4 NW 1/4 of Sec. 12, and 25 hectares (61.8 acres) in two separate privately owned parcels and approximately 9.3 hectares (23 acres) of State-owned lands in adjacent T14S, R15E, Sec. 11. This latter State parcel is a portion of the Mendota Wildlife Area, which is principally wetland waterfowl habitat subject to regular flooding.

The CDFG developed a draft management plan for the Alkali Sink Ecological Reserve in 1984 (finalized in 1990) (CDFG in litt. 1984). Management objectives were to be the protection of native alkali sink communities and the Reserves listed biota. Measures addressed in this draft plan included controlling grazing, fencing of reserve boundaries, encouraging maintenance of native species, restricting collecting and hunting, and precluding any development.

Williams reported in 1989 (in litt.) that management objectives for the Reserve had not been met and significant harm to the population had occurred.

USFWS prepared a Land Protection Plan for securing habitat for Fresno kangaroo rats through conservation easement or purchase (USFWS 1985b). The Land Protection Plan specified protection of 1,066 hectares (2,635 acres) of lands contiguous to critical habitat for Fresno kangaroo rats, along the northern border of the Alkali Sink Ecological Reserve. This plan was never implemented.

In 1988, additional inventory work was undertaken for Fresno kangaroo rats on natural lands in Merced, Madera, and Fresno Counties. Additional sites in the South Grasslands Waterfowl Management Area of Merced County were found to be inhabited by this species, but its subspecific classification is uncertain. Lack of access to private lands hampered thorough inventories elsewhere, but no Fresno kangaroo rats were found on any parcels in Fresno County that had extant populations in the 1970s and early 1980s. Attempts to locate Fresno kangaroo rats continued periodically in 1989, 1990, and 1991 without success (D.F. Williams unpubl. data).

In the Biological Opinion for the Friant Division Water Contract Renewals, habitat for the Fresno kangaroo rat was ranked highest in priority for protection by the Bureau of Reclamation (USFWS in litt. 1991). Before that could be accomplished, however, extant populations had to be located. Attempts to identify and inventory all potential habitat for Fresno kangaroo rats within their historical range, began in September 1992 and are continuing today. This effort was successful in finding only a single Fresno kangaroo rat, a male, on land already in State ownership. The Bureau of Reclamation also has funded a study of the population genetics and taxonomy of San Joaquin kangaroo rats. Principal objectives are to determine the range-wide genetic structure of the species and the degrees of differentiation of the various fragmented populations (Patton in litt. 1994). This work still is in progress.

The Endangered Species Recovery Program continued the search for extant populations of Fresno kangaroo rats and initiated management studies of kangaroo rats on the Kerman and Alkali Sink Ecological Reserves. Because there apparently are no extant populations on these reserves, the initial objectives are to measure population sizes of Heermanns kangaroo rats and vegetation characteristics on four plots, two on each Reserve. If future funds are provided, grazing could be initiated in future years and vegetation and population responses of Heermanns kangaroo rats measured. The goal would be to find a vegetation management regime that reduces populations of Heermanns kangaroo rats. Population responses to both grazing and burning are being tested in habitat for a small population of D. nitratoides on Lemoore Naval Ar Station, funded by the Navy and conducted by the Endangered Species Recovery Program. Additional population and vegetation management studies on Pixley National Wildlife Refuge, directed at determining appropriate habitat management for Tipton kangaroo rats, are expected to provide some information needed to manage habitat for Fresno kangaroo rats. This strategy assumes that Fresno kangaroo rats will be available for translocation to the Alkali Sink and Kerman Ecological Reserves. This will require that a population be located or that one or more of the extant populations peripheral to the historical range of the Fresno kangaroo rat prove to be genetically and taxonomically inseparable from Fresno kangaroo rats (Williams and Kelly in litt. 1994b, 1994c).

U.S. Environmental Protection Agency County bulletins governing use of rodenticides have greatly reduced the risk of significant mortality to Fresno kangaroo rat populations by State and county rodent-control activities. The California Environmental Protection Agency, California Department of Food and Agriculture, county agricultural departments, CDFG, and the U.S. Environmental Protection Agency collaborated with the Service in the development of County Bulletins that both are efficacious and acceptable to land owners (R.A. Marovich pers. comm.).

6. Recovery Strategy

Several pressing issues must be attended to now concerning recovery of the Fresno kangaroo rat. Answering the questions these issues pose is an integral first step in addressing recovery:

  1. The genetic relationships among extant isolated and scattered populations of San Joaquin kangaroo rats.
  2. Location and size of any extant Fresno kangaroo rat populations.
  3. How to manage natural lands to enhance habitat for Fresno kangaroo rats.

The second step to recovery involves instituting actions dictated by resolution of these issues, such as restoring and protecting of habitat, possibly translocating populations, and continuing management studies and population monitoring. The consolidation and protection of sufficient habitat for Fresno kangaroo rats to maintain a viable population cannot await the resolution of all these issues, though. There already is historical habitat in public ownership, though it is not sufficiently protected from catastrophes, such as flooding, nor appropriately monitored and managed for Fresno kangaroo rats. But, even with optimal habitat management, these parcels appear to be too small and vulnerable to both flooding and other catastrophes to provide the only refuges for the species. Thus, protection of the large block of natural land north of and between the Alkali Sink Ecological Reserve and the San Joaquin River and even larger blocks elsewhere is needed.

The largest existing block of natural land that was historical habitat for Fresno kangaroo rats is located in western Madera County (Williams 1990). Approximately 12,000 hectares (30,000 acres) are located in contiguous parcels. Fresno kangaroo rats still possibly exist on some part of this property, but access was given to Endangered Species Recovery Program to survey only two parcels comprising less than 10 percent of the total. Fresno kangaroo rats were not located on either parcel, though blunt-nosed leopard lizards, San Joaquin kit foxes, and palmate-bracted birds beak were seen or known from the sites or general area (Williams 1990, D.F. Williams unpubl. data). Because this area provides the highest potential for containing an extant population of Fresno kangaroo rats,and also is an important element in the recovery of palmate-bracted birds beak and blunt-nosed leopard lizards, protection and management of parcels there is considered of greater importance than elsewhere on parcels that are not known to be currently occupied.

The population of San Joaquin kangaroo rats at Lemoore Naval Air Station is the only one in public ownership in Kings County, and is endangered regardless of its taxonomic identity as the Fresno or Tipton kangaroo rat. Though the Navy has instituted habitat management studies on the parcel, it is too small to support a viable population indefinitely. The occupied site was formerly farmed, but then was retired to provide a motorcross track for Navy personnel. Kangaroo rats probably colonized the site by dispersing from the formerly-occupied land around a nearby runway. Restoration and enhancement of habitat next to the runway is not an option because this could attract birds and increase the probability of planes striking birds. Expansion of the existing habitat area by retiring land next to the motorcross site and managing it appropriately is important to maintaining the kangaroo rat population. Because the land is owned by the U.S. Government and is part of the air station, acquisition would not be needed, and the loss of revenue from the agricultural lease would be small compared to the cost of protecting habitat elsewhere. The amount of land needed cannot be calculated precisely now, but the initial addition of 32 to 65 hectares (80 to 160 acres) to the 38 hectares (97 acres) of existing habitat would provide space and habitat for an expanding population. The sooner this is accomplished, the greater the chances that the population can be saved.

Restoration of habitat and, if necessary, reestablishment of Fresno kangaroo rats on the Alkali Sink and Kerman Ecological Reserves also are elements of the recovery of the species, but until management issues, including protection from flooding, are resolved, these have lower priority. Reducing the accumulation of mulch and ground cover of weedy grasses has priority over other management issues on these reserves. Restoration to optimal conditions at the Kerman Reserve for Fresno kangaroo rats may also require establishment of saltbushes and other shrubs.

Size of occupied habitat areas for recovery ideally should be several thousand acres each, but no existing or potential habitat area comes near to the minimum desirable size. Therefore, criteria are scaled to size of existing and potential habitat areas. With habitat management, these parcels should be adequate to support populations. Three separate populations reduce the risk of extinction by environmental catastrophes, and considerably enhance the prospects of recovery. A larger number of separate populations is possible, but obtaining more than four large populations on public lands probably is not very practical given the amount and distribution of natural lands within the historic range of the species.

Recovery Actions.-- Recognizing that genetic and taxonomic studies (Patton in litt. 1994, J.L. Patton pers. comm.) and habitat surveys already are in progress, critical recovery actions needed now are:

  1. Complete the studies on relationships and taxonomic identity of isolated populations of San Joaquin kangaroo rats.
  2. Intensify and continue efforts to locate populations of Fresno kangaroo rats within the historical range of the species. If a population is found, captive breeding should be considered as a recovery option depending on the size of the population.
  3. Continue and increase habitat management studies.
  4. Restore additional habitat for D. nitratoides at Lemoore Naval Air Station.
  5. Protect natural land between the Alkali Sink Ecological Reserve and the San Joaquin River to the north (SandyMush Road/South Grasslands Area).
  6. Begin discussion and planning for conservation of natural lands in western Madera County; acquire title or easement to appropriate parcels from willing sellers.

Recovery actions that also are needed, but after critical actions are implemented or completed are:

  1. Protect additional habitat for Fresno kangaroo rats in Kings County, where populations of the species are discovered. Habitat should be in blocks of at least 384 hectares (950 acres), preferably larger, with one block no less than 1,012 hectares (2,500 acres).
  2. Work with landowners in western Madera County to determine presence or absence of the species there. If a population is found, assess translocating populations to public lands in Fresno County.
  3. Restore habitat for Fresno kangaroo rats on the Alkali Sink and Kerman Ecological Reserves. Restoration should include manipulation of the plant community to favor Fresno kangaroo rats over Heermanns kangaroo rats.
  4. Reintroduce Fresno kangaroo rats to restored and unoccupied habitats on ecological reserves and newly-protected parcels.
  5. Monitor all populations and their supporting biotic communities annually for a 10-year period, then at 3-year intervals until recovery is achieved.
  6. Manage habitat for Fresno kangaroo rats as needed.

© CSU Stanislaus, Endangered Species Recovery Program
Dept. of Biological Sciences
One University Circle, Turlock, California 95382

Information Contact: esrpinfo [at] esrp.org