San Bernardino Merriam's Kangaroo Rat

Dipodomys merriami parvus

Description

San Bernardino Merriam's kangaroo rat has a body length of about 3.7 in (9.4 cm) and a total length of 9-9.3 in (22.9-23.6 cm). The hind foot measures less than 1.4 in (3.6 cm) in length. The body color is weakly ochraceous (yellow) with a heavy overwash of dusky brown. The tail stripes are medium to dark brown and the foot pads and tail hairs are dark brown. The flanks and cheeks of the subspecies are dusky. The San Bernardino kangaroo rat is considerably darker and much smaller than either of the other two subspecies of Merriam's kangaroo rat in southern California, Dipodomys merriami merriami and D. m. collinus. The San Bernardino kangaroo rat is one of the most highly differentiated subspecies of D. merriami, and it seems likely that it has nearly achieved species rank. This differentiation is likely due to its apparent isolation from other members of D. merriami.

Behavior

Home ranges for the San Bernardino Merriam's kangaroo rat average 0.8 acres (0.3 hectares) for both males and females. Long sallies (bursting movements) of 328 ft (100 m) or more beyond these ranges are not uncommon. Although outlying areas of their home ranges may overlap, adults actively defend small core areas near their burrows. Home range overlap between males and between males and females is extensive, but female-female overlap is slight. Pregnant San Bernardino Merriam's kangaroo rats have been found from February through October, and immature individuals have been found from April through September. Some females may produce more than one litter per year. Litter size averages between two and three young. Similar to other kangaroo rats, the San Bernardino kangaroo rat is primarily granivorous and often stores large quantities of seeds in surface caches. Green vegetation and insects are also important seasonal food sources. Insects, when available, have been documented to constitute as much as 50% of a kangaroo rat's diet. Females are known to increase ingestion of foods with higher water content during lactation, presumably to compensate for the increased water loss associated with milk production. D. merriami are known for their ability to live indefinitely without water on a diet consisting entirely of dry seeds.

Habitat

In most heteromyids, soil texture is a primary factor in determining species' distributions. San Bernardino kangaroo rats are found primarily on sandy loam substrates, characteristic of alluvial fans and floodplains, where they are able to dig simple, shallow burrows.

The San Bernardino kangaroo rat is now primarily associated with a variety of sage scrub vegetation, where the common elements are the presence of sandy soils and relatively open vegetation structure. Where the San Bernardino kangaroo rat occurs in alluvial scrub, the subspecies reaches its highest densities in early and intermediate seral stages. Alluvial scrub includes elements from chaparral, coastal sage, and desert communities. Three successional phases of alluvial scrub have been described: pioneer, intermediate, and mature alluvial scrub. The distribution of these phases is influenced by elevation, distance from the main channels, and the time since previous flooding. Vegetation cover generally increases with distance from the active stream channel. The pioneer, or youngest phase, is subject to frequent disturbance, and vegetation is usually renewed by annual floods. The intermediate phase, defined as the area between the active channel and mature terraces, is subject to periodic flooding at longer intervals. The vegetation on intermediate terraces is relatively open and supports the highest densities of the San Bernardino kangaroo rat. The mature phase is rarely affected by flooding and supports the highest plant cover. Flood events break out of the main river channel in a complex pattern, resulting in a braided appearance to the floodplain. Not all the alluvial scrub habitat is suitable for the kangaroo rat at any point in time. The San Bernardino kangaroo rat, like other subspecies of Merriam's kangaroo rat, prefers open habitats characterized by low shrub canopy cover (mostly 7-22%) and rarely occurs in dense vegetation. Therefore, the older seral stages of the floodplain vegetation are generally less suitable for this subspecies.

Distribution

Based on the distribution of suitable (sandy) soils and the historical collections of this subspecies, the historical range is thought to have encompassed an area of approximately 326,467 acres (132,117 hectares). Although the entire area of the historical range would not have been occupied due to variability in vegetation and soils, the San Bernardino Merriam's kangaroo rat was apparently widely distributed across this area. By the 1930s the habitat had been reduced to approximately 28,000 acres (11,331.2 hectares). In 1997 the San Bernardino kangaroo rat was known to occupy approximately 3,247 acres (1,314 hectares) of suitable habitat divided unequally among seven locations that were widely separated from one another. Four of these locations—City Creek, Etiwanda, Reche Canyon, and South Bloomington—support only small, remnant populations. The remaining locations (the Santa Ana River, Lytle and Cajon washes, and San Jacinto River) contain the largest extant concentrations of kangaroo rats and blocks of suitable habitat. Based on further review of available information, the Santa Ana River, Lytle and Cajon washes, and the San Jacinto River are estimated to have additional habitat that is likely occupied, at least in part, by the San Bernardino kangaroo rat.

Threats

Threats to all of the remaining populations of San Bernardino Merriam's kangaroo rat include habitat loss, destruction, degradation, and fragmentation due to sand and gravel mining operations, flood control projects, urban development, off-highway vehicle use, or some combination of these. In addition, the three largest remaining populations of this subspecies are endangered due to their small size and to habitat loss caused by changes in the natural stream flow regime, including seasonal flooding and associated modification of plant succession patterns. Loss and fragmentation of San Bernardino kangaroo rat habitat is expected to continue as southern California's human population expands. In the 1950s the population of Riverside and San Bernardino counties combined was about 400,000. The population of these counties was expected to increase to nearly 4 million by 2000. Further habitat losses resulting from development or alteration of the landscape will likely have a significant adverse effect on the viability of remaining San Bernardino Merriam's kangaroo rat populations.

Conservation and Recovery

The San Bernardino Valley Water Conservation District and the Bureau of Land Management are coordinating with the U.S. Fish and Wildlife Service and others to develop a regional conservation plan that attempts to reconcile conflicts among competing land uses, including the conservation of the San Bernardino kangaroo rat. Existing laws that may provide some protection for the San Bernardino kangaroo rat include 1) the California Environmental Quality Act and the National Environmental Policy Act; 2) the California Natural Community Conservation Planning Program; 3) the Surface Mining Control and Reclamation Act; 4) the California Endangered Species Act; 5) conservation provisions under the Federal Clean Water Act; 6) land acquisition and management by federal, state, or local agencies or by private groups and organizations; and 7) local laws and regulations.

Contacts

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

Carlsbad Fish and Wildlife Office
2730 Loker Avenue West
Carlsbad, California 92008-6603
Telephone: (760) 431-9440
Fax: (760) 431-9624

Reference

U. S. Fish and Wildlife Service. 24 September 1998. "Final Rule to List the San Bernardino Kangaroo Rat as Endangered." Federal Register 63 (185) 51005-51017.