Endangered Species Recovery Program
Taxonomy.-- The Tipton kangaroo rat is one of three subspecies of the San Joaquin kangaroo rat. The type specimen of the Tipton kangaroo rat was collected from Tipton, Tulare County, California, in 1893 (Merriam 1894). See account of the Fresno kangaroo rat for a discussion of taxonomic history of D. n. nitratoides. Hafner (1979) examined samples of Tipton and short-nosed kangaroo rats, and, using detailed analyses, established better-defined boundaries between the two subspecies than those of previous researchers. He concluded that samples from populations northeast and east of Bakersfield, and in upland saltbush communities above the southern and eastern borders of the Tulare Basin floor were characteristic of populations of short-nosed kangaroo rats, typified by reference samples from the Carrizo Plain, San Luis Obispo County. Hafners (1979) analyses showed that the subspecies boundary on the southwest in Kern County nearly coincided with the California Aqueduct, which is positioned just above the Valley floor along the edge of the more steeply sloping foothills in areas that do not flood extensively. The natural boundary between these two subspecies on the southwest was probably a narrow zone of seasonal and permanent wetlands around Kern and Buena Vista lakes and the Kern River channel that meandered north from the east edge of the Elk Hills to historical Goose Lake. Historical barriers between the two subpecies probably were intermittent in some spots. More recent flood control and diversion of waters from the Kern River for irrigation and other purposes removed these barriers and probably allowed for increased genetic exchange between the two subspecies. Today, the California Aqueduct and large expanses of irrigated cropland again have isolated these populations.
Description.-- See account of the Fresno kangaroo rat for a general description of the species. On average, adult Tipton kangaroo rats weigh about 35 to 38 grams (1.23 to 1.34 ounces), have a head and body length of about 100 to 110 millimeters (3.94 to 4.33 inches) and a tail about 125 to 130 millimeters (4.92 to 5.12 inches) in length. The Tipton kangaroo rat is larger than the Fresno kangaroo rat and smaller than the short-nosed kangaroo rat.
Identification.-- See the Fresno kangaroo rat account for distinguishing Tipton kangaroo rats from other co-occurring species. The Tipton kangaroo rat can be distinguished from the Fresno kangaroo rat by its larger average measurements: total length for males, 235 millimeters (9.25 inches), for females, 221 millimeters (8.7 inches); length of hind foot for males 34.7 millimeters (1.37 inches), for females, 33.6 millimeters (1.32 inches); mean inflation of the auditory bullae for males, 22.1 millimeters (0.87 inch), for females, 21.8 millimeters (0.86 inch) (Hoffmann 1975) (see accounts of Fresno and short-nosed subspecies for corresponding average measurements).
Historical Distribution.-- The historical geographic range of Tipton kangaroo rats (Figure 45) was estimated to cover approximately 695,174 hectares (1,716,480 acres) (Williams 1985). Tipton kangaroo rats were distributed within an area on the floor of the Tulare Basin, extending from approximately the southern margins of Tulare Lake on the north; eastward and southward approximately along the eastern edge of the Valley floor in Tulare and Kern Counties. The southern and western extent of their range was the foothills of the Tehachapi Mountains (south) and the marshes and open water of Kern and Buena Vista lakes, and the sloughs and channels of the Kern River alluvial fan. Farther north, the western boundary was approximately along the Buena Vista slough of the Kern River channel into Goose Lake. The approximate line on the northwest is marked by the city of Lost Hills, Kern County; Kettleman City, Kings County; and Westhaven, Fresno County. Prior to development of water-diversion and irrigation systems over the past several decades, this area bounded three large lakes, Tulare, Kern, and Buena Vista, together with marshlands that were unsuitable habitat for kangaroo rats (Boolootian 1954, Hoffmann 1974, Hafner 1979, Williams et al. 1993a, Williams 1985).
Current Distribution.-- By July 1985, the area inhabited had been reduced, primarily by cultivation and urbanization, to about 25,000 hectares (63,000 acres), only about 3.7 percent of the historical acreage. Additional small parcels not surveyed by Williams (1985) have since been found to be inhabited. Tipton kangaroo rats also have reinhabited several hundred to a few thousand acres that were in crop production in 1985 but have since been retired because of drainage problems or lack of water, or acquired by State and Federal agencies for threatened and endangered species conservation. Most notable has been a mix of mostly agricultural and some natural land on the Kern Fan Element, some of which is now within the Kern Water Bank Habitat Conservation Plan area. This project provides over 4,000 hectares (10,000 acres) of habitat for threatened and endangered species, though a lesser, unknown amount actually has been naturally recolonized from adjacent natural land. Offsetting these gains has been the loss of several hundred to a few thousand acres of habitat that have been developed. Thus, the current acreage of occupied habitat is unknown, but probably does not differ much from the 1985 estimate.
Current occurrences are limited to scattered, isolated areasclustered west of Tipton, Pixley, and Earlimart, around Pixley National Wildlife Refuge, Allensworth Ecological Reserve, and Allensworth State Historical Park, Tulare County; between the Kern National Wildlife Refuge, Delano, and in natural lands surrounding Lamont (southeast of Bakersfield), Kern County; at the Coles Levee Ecosystem Preserve; and other, scattered units to the south in Kern County (Figure 45).
Food and Foraging.-- Tipton kangaroo rats eat mostly seeds, with small amounts of green, herbaceous vegetation and insects supplementing their diet when available. Most aspects of food and foraging of Tipton kangaroo rats are identical to those of Fresno kangaroo rats. See the account of the Fresno kangaroo rat for more information.
Reproduction and Demography.-- Little specific information has been published on reproduction of Tipton kangaroo rats. Generally, this aspect of their biology is extremely similar to that of the Fresno kangaroo rat (see that account for details). Five Tipton kangaroo rats being held in captivity to prevent their death by permitted destruction of their habitats each gave birth to two young (D.J. Germano pers. comm., D.F. Williams unpubl. observ., S. Yoerg pers. comm.).
Reproduction commences in winter and peaks in late March and early April (Figure 46). Most females appear to have only a single litter, though some adult females have two or more, and females born early in the year also may breed (Endangered Species Recovery Program unpubl. data).
Figure 46. Percentage of reproductive female Tipton kangaroo rats
At the Paine Wildflower Preserve south of Kern National Wildlife Refuge, Clark et al. (1982) estimated a density of 2.6 Tipton kangaroo rats per hectare (1.05 per acre) in the "best" habitat above flood level, and 1.5 per hectare (0.61 per acre) in "poor" habitats subjected to flooding and disturbance by past disking of the soil. Hafner (1979) estimated relative densities of Tipton kangaroo rats at 13 sites representing areas from throughout the geographic range and most plant communities in which Tipton kangaroo rats were known to occur. Densities ranged from a low of 1 to 2 per hectare (0.4 to 0.8 per acre) in alkaline and terrace grasslands with a sparse cover of seepweed to a high of about 7 to 9 per hectare (2.8 to 3.6 per acre) in saltbush scrub.
In 1985, surveys through the remaining extant habitat resulted in estimated densities, based on numbers of burrow systems, ranging from less than 1 per hectare to 50 per hectare (less than 0.4 to 20.2 per acre). Areas supporting very low densities had few noticeable features in common. Sites on the eastern perimeter of the geographic range in terrace grasslands had consistently low densities. Areas subjected to prolonged flooding also supported few kangaroo rats.
At Pixley National Wildlife Refuge on two plots, density estimates in June 1991 during drought were 3.0 to 3.8 Tipton kangaroo rats per hectare (1.2 to 1.5 per acre). After the end of a 5.5 year drought in April 1991, a population irruption occurred, and peaked in January 1993. Subsequently, density declined from the high of 88.2 per hectare (35.7 per acre) in January 1993 to a low of 1.1 per hectare (0.45 per acre) in April 1995. The shape of this population decline is illustrated by the number of Tipton kangaroo rats known to be alive each month in Figure 47 (Endangered Species Recovery Program unpubl. data). During the decline, annual rainfall was greater than average and little or no livestock grazing occurred in the pasture where the plot was located. Kangaroo rats could not use their usual defenses of speed and alertness, adaptations for habitats with sparse, low vegetation, and many may have been taken by predators. High rainfall also may have caused death from water penetrating burrows and drowning occupants, spoiling seed stores, or causing death from hypothermia or pneumonia-like diseases that have been observed to afflict these animals when placed in a cool, moist environment (Endangered Species Recovery Program unpubl. observ.).
Figure 47. Number of Tipton kangaroo rats known to be alive each month
Behavior and Species Interactions.-- Tipton kangaro rats live in ground burrows. Most burrows probably are dug by the occupant or a predecessor of the same species. Burrows are typically simple, but may be unbranched or branched, including interconnecting tunnels. Most burrows are less than 25 centimeters (10 inches) deep (Germano and Rhodehamel 1995). Nothing else specific to the behavior of the Tipton subspecies has been published (see Fresno kangaroo rat for a general discussion of behavior and species interactions).
Tipton kangaroo rats are food for a variety of predators: coyotes, San Joaquin kit foxes, long-tailed weasels, American badgers, owls, hawks (San Joaquin kangaroo rats infrequently emerge from their burrows during daylight; Tappe 1941, Williams et al. 1993b), various species of snakes, and probably others. Except for small, isolated populations, predation is unlikely to threaten Tipton kangaroo rats. The increasing fragmentation of the range of Tipton kangaroo rats, however, increases the vulnerability of small populations to predation.
Habitat and Community Associations.-- Tipton kangaroo rats are limited to arid-land communities occupying the Valley floor of the Tulare Basin in level or nearly level terrain. They occupy alluvial fan and floodplain soils ranging from fine sands to clay-sized particles with high salinity. Historically, populations apparently were most numerous and persistent in Relictual Interior Dune Grassland and Sierra-Tehachapi Saltbush Scrub communities. Today, much of the occupied remnants of their range have one or more species of sparsely scattered woody shrubs and a ground cover of mostly introduced and native annual grasses and forbs. Woody shrubs commonly associated with Tipton kangaroo rats are: spiny and common saltbushes, arrowscale (Atriplex phyllostegia), quailbush (Atriplex lentiformis), iodine bush, pale-leaf goldenbush, and honey mesquite (Prosopis glandulosa var. torreyana). A conspicuous semiwoody species is seepweed (Williams 1985).
Important existing communities for Tipton kangaroo rats are iodine bush shrubland (Valley Sink Scrub) and Valley Saltbush Scrub (Griggs et al. 1992). Winter rains and runoff from the surrounding mountain ranges (Sierra Nevada to the east, Tehachapi Mountains to the south, and Temblor Range to the west) flood much of these low-lying communities occupied by Tipton kangaroo rats. Areas with standing water during portions of winter and spring (vernal pools) become alkaline playas when the water has evaporated allowing Tipton kangaroo rats to recolonize these areas even though alkaline water lies close to the surface of the soil, year around. Presumably during flooding, individuals are either drowned or captured by predators after being forced from their burrows, or escape to higher ground (Williams 1985).
Although Tipton kangaroo rats occur in terrace grasslands devoid of woody shrubs, sparse-to-moderate shrub cover is associated with populations of high density. Typically, however, burrow systems are located in open areas; only in areas of dense shrub cover are burrows usually located beneath shrubs. Terrain not subject to flooding is important for permanent occupancy by Tipton kangaroo rats.
Burrows of Tipton kangaroo rats are commonly located in slightly elevated mounds, the berms of roads (where placed above ground level), canal embankments, railroad beds, and bases of shrubs and fences where windblown soils accumulate above the level of surrounding terrain. Soft soils, such as fine sands and sandy loams, and powdery soils of finer texture and of higher salinity are generally associated with greater densities of Tipton kangaroo rats than are less saline and alkaline, sandy-loam, loam, and clay-loam soils of portions of the eastern margins of their geographic range, supporting terrace grasslands. This may relate to how crumbly the soils are, the type of plant communities they support, or both (Williams 1985).
At Pixley National Wildlife Refuge, Tipton kangaroo rats are the most numerous small mammal. They dominate grazed annual grassland on the refuge, where they typically outnumber Heermanns kangaroo rats, the second most numerous species. Other common, mall mammalian associates are San Joaquin pocket mice and deer mice (Williams and Germano 1991, D.F. Williams unpubl. data). Other common, mammalian associates include San Joaquin kit foxes, coyotes, American badgers, California black-tailed hares, California ground squirrels, harvest mice, and house mice.
Reasons for Decline.-- The principle reason for the decline of Tipton kangaroo rats was the loss of habitat due to agricultural conversion. Agriculture followed the gold rush of the 1850s, first developing on the nonsaline soils of the alluvial flood plains and forests of the eastern Valley. This probably only had a minor impact to habitat for Tipton kangaroo rats. The later construction of dams and canals produced a dependable supply of water for the Valley. This in turn allowed the cultivation of the alkaline soils of the saltbush and valley sink scrub and relictual dune communities, and was principally responsible for the decline and endangerment of the Tipton kangaroo rat.
As recently as the early 1970s, just after the completion of the Central Valley and State Water Projects, only about 1.4 million hectares (3.5 million acres) in the San Joaquin Valley were in irrigated cultivation--most of the total was in the San Joaquin Basin (approximately the northern half of the Valley). By 1978, however, only about 195,000 hectares (370,000 acres) out of a total of about 3.4 million hectares (8.5 million acres) on the San Joaquin Valley floor remained as non-developed land (Williams 1985).
An aerial survey conducted in late 1983, together with selected ground inspections and other sources of information provided an estimate of 44,562 hectares (110,031 acres) of undeveloped land out of a total of 1,035,296 hectares (2,556,288 acres) on the floor of the Tulare Basin (Werschkull et al. 1984). Ignoring minor differences between the boundaries of the 1983 survey and the investigations by Williams (1985), only about 30,549 hectares (75,430 acres) were undeveloped in June 1985. Remaining natural lands represented the least desirable for development in the basin.
The use of rodenticides to control California ground squirrels probably contributed to the decline or elimination of small populations of Tipton kangaroo rats, isolated and surrounded by agricultural land. Urban and industrial development and petroleum extraction all have contributed to habitat destruction, though not on a scale comparable to agricultural development (Williams 1985).
Threats to Survival.-- Current threats of habitat destruction or modifications rendering areas unsuitable for Tipton kangaroo rats come from industrial and agriculturally-related developments, cultivation, the formation of heavy thatch by exotic grasses, and urbanization, and secondarily from flooding. Nearly every parcel of land in private ownership that is currently inhabited by Tipton kangaroo rats is surrounded by cultivated fields or urbanized land where these animals cannot live. Nearly all remaining natural land is of poor agricultural potential, having saline soils and high water tables, and more than half is subject to winter flooding (Williams 1985).
Because of the large amount of salts in soils on the Tulare Basin floor, lack of natural drainage to the ocean, and the desert climate, build up of salts in the soil and saline-saturated fields threatens agriculture over large areas (San Joaquin Valley Interagency Drainage Program 1990). Most of the remaining habitat of Tipton kangaroo rats is in areas that are already flooded periodically. Several parcels with extant natural lands in the 1970s now have private evaporation ponds into which salt-laden drain waters are being diverted. Unless other solutions are found for drainage problems, including land retirement, more habitat for Tipton kangaroo rats probably will be lost to this purpose (Williams 1985).
In addition to being federlly-listed as endangered in 1988 (USFWS 1988), the Tipton kangaroo rat was listed by the State of California as Endangered in 1989 (Table 1; Williams and Kilburn 1992). Mitigation actions and compensation funds to purchase natural lands providing habitat for Tipton kangaroo rats have resulted in preservation of portions of key areas in the Allensworth Ecological Reserve, Semitropic Ridge, Kern Fan areas, and more scattered parcels elsewhere (Table 2).
Habitat management studies on Pixley National Wildlife Refuge, which provides some of the best remaining habitat for Tipton kangaroo rats, were initiated in 1991 (Williams and Germano 1991), and expanded in 1992 (Engler and Chapin 1993). The CDFG also has begun to census its properties and investigate habitat management in the Allensworth Ecological Reserve (Potter 1993). The Bureau of Reclamation and USFWS have supported a study of population ecology of Tipton kangaroo rats at Pixley National Wildlife Refuge by the Endangered Species Recovery Program since December 1992 (Endangered Species Recovery Program unpubl. information). CDFG also has recently instituted habitat management investigations and experimentation on part of Allensworth Ecological Reserve (M. Potter and G. Presley pers. comm.).
U.S. Environmental Protection Agency County bulletins governing use of rodenticides have greatly reduced the risk of significant mortality to Tipton 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.).
The major issues in recovering the Tipton kangaroo rat are habitat management and protection of blocks of their natural or restored habitat to maintain viable populations. The species populations periodically irrupt to high levels and decline rapidly, often going extinct locally. Local extinctions or near extinctions may be caused by long-term drought, excessive amounts of precipitation, flooding, and perhaps other, less well known factors. When large expanses of connected habitat existed, local extinction was not a great problem because some surviving populations eventually irrupted and individuals recolonized areas where they had been eliminated. Contributing to this pattern of population dynamics is competition with Heermanns kangaroo rats, which are much larger, more general in their habitat requirements, and more successful in maintaining populations in a fragmented landscape. At times when the environment is poorly suited to Tipton kangaroo rats, competition with Heermanns kangaroo rats may cause elimination of the former. Because of the fragmentation and isolation of remaining habitat, when these natural processes ensue, local extinction without opportunity for later recolonization results. This process already has run or nearly run its course with Fresno kangaroo rats. There are several blocks of habitat for Fresno kangaroo rats left, ranging from about 16.2 hectares (40 acres) to several from about 259 to 2,023 hectares (640 to 5,000 acres), and one of about 12,141 hectares (30,000 acres), yet none are known to harbor Fresno kangaroo rats. Because the decline and fragmentation of Tipton kangaroo rat habitat has occurred much more recently, probably a similar fate awaits it unless there is management intervention, and conservation lands for this species are sufficiently large and diverse to reduce or eliminate the adverse effects of some environmental processes. Thus, the two key elements of a recovery strategy for Tipton kangaroo rats are:
These blocks should be of several thousand acres each with a core of at least 2,000 hectares (about 5,000 acres) of high quality habitat that is not subject to periodic flooding from overflowing streams or sheet flooding from torrential rain. They should provide topographic diversity and diversity of plant communities. The vegetation should be actively managed by an appropriate level of livestock grazing to prevent excessive accumulation of mulch and growing plants until such time as optimum management conditions are determined by scientific research.
The existing configuration of the natural land-developed land mosaic is such that it is impractical and too expensive to propose reconnecting the large blocks of land in Tulare and northern Kern and southern Kings Counties with the lands on the western edge of the Valley and the isolated blocks in the southern end of the Valley. Instead, by protection of additional natural land and restoration of contiguous agricultural land with drainage problems, sufficient habitat in three areas can be protected economically: the Kern Fan area; the Pixley National Wildlife Refuge-Allensworth Natural Area, and the Kern National Wildlife Refuge-Semitropic Ridge area.