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Old Baldy, Canada | photo by Cameron Schaus

Sierra Club
Santa Cruz kangaroo ratís decline indicates a plant community at risk
by Debbie Bulger and Caitlin Bean


kangaroo rat  

 
The Santa Cruz kangaroo rat (Dipodomys venustus venustus ) never was very widespread in its occurrence. Historically, it ranged from Belmont, south of San Francisco through the Santa Cruz Mountains to approximately Corralitos. Where once its range encompassed much of Santa Cruz County and parts of San Mateo and Santa Clara Counties, recently it has been found on only one parcel in the Santa Cruz Mountains.

Its habitat and population have diminished at an alarming rate over the last quarter century.

Named for its hind legs which are well adapted for jumping locomotion, kangaroo rats are nocturnal rodents more closely related to gophers than to rats. Like gophers, kangaroo rats have fur-lined cheek pouches perfect for gathering seeds, their main food. Typically they are found in arid areas where most species do not need to drink water. However, the Santa Cruz kangaroo rat is unusual in that it has adapted to living in our temperate climate and actually drinks free water.

There are 23 species or subspecies of kangaroo rats found only in California. Five of these are listed under the Federal Endangered Species Act. Five additional species or subspecies are listed as “Species of Special Concern” by the California Department of Fish and Game. The Santa Cruz kangaroo rat is not listed as endangered by either the state or the federal government although it appears to meet the criteria for listing.

It is tottering on the brink of extinction. Not only are its numbers down and its range contracted, it appears to be suffering from low genetic diversity which puts its existence at even greater risk. Its relatively long life for a rodent (four to five years) and slow maturation rate allow for the survival of adults during droughts. This adaptation does not result in high production of young—a fact which may have contributed to its decline.

  kangaroo rat
  Its unusually long tail provides the kangaroo rat with balance when jumping.

And it is not alone. The kangaroo rat is considered a “keystone” species. That means that its activities have great influence on the plants and animals that occupy the same habitat. This effect of the kangaroo rat was documented by Jim Brown and Ed Heske in 1990 when they published the findings of their 10-year field experiment in which they excluded kangaroo rats from specific areas in the Chihuahuan desert. These researchers discovered that absence of kangaroo rats resulted in a major change in the vegetation cover and the species composition within the exclosures (i.e., desert shrubland was converted to grassland!). Some species did not do as well as they would have in the presence of the kangaroo rat. In other words, kangaroo rats had a role in maintaining a healthy functioning ecosystem.

Kangaroo rats dig burrows, move seeds around and cache seeds—activities which are beneficial to other species.
It has been suggested that in California, kangaroo rats are indicators of the health of the very ecosystem which they inhabit. Like the famous canary in the coal mine, their decline may be an early warning sign of the decline of entire natural communities.

The community which the Santa Cruz kangaroo rat inhabits is unusual indeed. These small, long-tailed rodents live in a plant community called “silverleaf manzanita mixed chaparral” which is found on inland marine sand deposits. This plant community is one of only two that comprise the Zayante sand hills ecosystem which supports not only the Santa Cruz kangaroo rat, but also at least 11 rare plants and three rare animal species, many found nowhere else in the world.

The Zayante sand hills are characterized by manzanita, including the rare silverleaf manzanita, ponderosa pine, coyote bush and other chaparral plants. Their soft, well-drained sand provides an ideal soil for digging burrows, but also make this area attractive for sand quarrying.

Due to land use decisions over the years, the historically limited and fragmented amount of silverleaf manzanita chaparral has steadily decreased. Urbanization has accounted for much of the loss of the historic range of the Santa Cruz kangaroo rat. In addition, a large portion of the once intact sandhills ecosystem has been directly destroyed by sand mining operations.

It has been estimated that historically a total of 3,121 acres of this plant community existed in Santa Cruz County. A 1994 estimate suggested that about 400 acres had been altered by residential development, 350 acres had been removed for sand quarrying, and another 400 acres developed as landfills and commercial property. In the nine years since that estimate, it is likely that the total amount of silverleaf manzanita chaparral has decreased markedly. The decline of the distribution and numbers of Santa Cruz kangaroo rats point to that very conclusion.

Other threats to the Santa Cruz kangaroo rat include predation by cats, recreational uses such as off-road mountain biking and horseback riding, and fire suppression.

Given the fact that the Santa Cruz kangaroo rat has a narrow geographic range, specialized habitat requirements, and is known to occur only in small populations, it appears there is a high probability of its becoming extinct in the near future. For this reason, Caitlin Bean is petitioning both the Federal Government and the State of California to list this species as endangered.


A large portion of the once intact sandhills ecosystem has been directly destroyed by sand mining operations.  
A large portion of the once intact sandhills ecosystem has been directly destroyed by sand mining operations.

 
It’s all connected

This last half-century has been marked by a passionate effort to save the earth’s biodiversity, but species continue to slip quietly into oblivion. Why should people be concerned about the extinction of small mammals such as kangaroo rats, amphibians such as long-toed salamanders or even insects? The famous biologist E.O. Wilson wrote, “Each species, to put the matter succinctly, is a masterpiece.”

Each species plays a role in its ecosystem that other species may be dependent upon. In addition, each species is a source of knowledge and aesthetic pleasure. However, one of the most compelling arguments to care about these creatures is that each extinction sends a message that we are fouling our home. What is bad for nature is almost certainly bad for us. Our efforts to protect these resources help to insure that future generations will be able to enjoy nature the way we have.


How you can help:
  • Avoid bike and horse riding in the fragile Zayante soils (especially in silverleaf manzanita chaparral habitat patches).
  • Respect trail closures for endangered species management.
  • Avoid constructing trails in the highly erosive Zayante soils.
  • Support prescriptive fire efforts in maritime chaparral habitats.
  • Contribute to local land preservation efforts.
  • If you live adjacent to silverleaf manzanita chaparral, please keep your cats indoors.
  • If you have maritime chaparral on your property and would like to know if it provides habitat for the Santa Cruz kangaroo rat, call Caitlin Bean, 423-2348; her research is ongoing.
  • Contact the Sand Hills Alliance for Natural Diversity (SAND), a group formed to preserve our rare and unique sandhills habitat and inspire stewardship through scientific research, public education, and integrated land use planning. SAND participants come from a variety of backgrounds, and include landowners, biologists, planners, and other concerned citizens. SAND meets each month to discuss a variety of sandhills conservation issues. Participants help preserve sandhills habitat, lead community educational programs, conduct scientific research, and help direct management for sandhills habitat. SAND advises on many types of sandhills related projects, providing science-based information for successful conservation. In the spring, SAND leads guided walks to see the amazing wildflowers of the sandhills. For more information, contact Jodi McGraw.

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