The sagebrush steppe, an open, mostly treeless grassland, is an iconic
Western habitat that is being threatened throughout much of its range.
In California, the sagebrush ecosystem is found primarily at lower
elevations of coastal southern portions of the state. This habitat is typically
arid, with sandy loam substrates and widespread alluvial fans, the
fan-shaped deposits that form when a stream broadens as it opens to
a flood plain. Ephemeral streams—streams that flow only during and
briefly after periods of rain—are also commonly found in this ecosystem.
The amount of plant growth varies depending on how frequently
the area floods. Major flooding prevents plants from taking hold and
spreading, while infrequent flooding allows native plants—including scrub
sage, chaparral, buckwheat and grasses, and coastal cacti—to flourish. The
San Bernardino kangaroo rat relies on an intermediate sage brush habitat,
one that has moderately infrequent flooding and patchy plant cover with
plenty of sandy loam for burrowing.

This bi-pedal rodent with its long tail and soft fur is one of the smaller sized kangaroo ratsrodents that are known for drumming with their feet. Highly adapted to arid conditions and the natural flood cycles of their habitat, kangaroo rats don’t need drinking water, requiring only the moisture in their food to survive. They rely on their sage scrub habitat for two features critical to their survival and reproduction: alluvial fans and seed banks. The loose  sand in the alluvial fans provides sand-bathing sites where rats clean oils from their hair; the oil then acts as a scent marker to communicate the rat’s identity to its neighbors. Seeds banks provide their key food; the rats harvest seeds and carry them in specialized, fur-lined cheek pouches, caching the food in sandy areas for future consumption. Even the green vegetation that grows after flooding plays a key role in the species survival, as it stimulates reproduction.

Water in the Balance

Dry washes and intermittent ephemeral streams in arid parts of the American West provide forage, cover, nesting, and movement corridors for wildlife. Functionally, these areas moderate soil and air temperatures, stabilize channel banks, promote seed banking, and trap silt and fine sediment, providing habitat to diverse plants and animals. Rainfall and flood flows often trigger pulses of germination in ephemeral streambeds, and the annual and perennial plants found here provide food for wildlife. Because ephemeral stream bed deposits are often looser than the soils of surrounding uplands, they are especially important habitat for sand-burrowing species like the kangaroo rat.

The San Bernardino kangaroo rat has declined as its habitat in southern California has been heavily developed for residential and commercial purposes.

Development fragments their habitat and populations, resulting in inbreeding and the consequent vulnerability to genetic defects. Over 90 percent of the San Bernardino kangaroo rat’s habitat has been destroyed by development, and what remains has been hydrologically altered by dams and flood-control measures. Water-management practices that divert or stop the flow of water in the washes and streams prevent natural cycles of flooding. Without sufficient flooding, scrub plants flourish, and the ecosystem converts from intermediate to mature, with dense plant growth overtaking the sandy loam substrate required by the kangaroo rat.