The Riparian Brush Rabbit: California’s Endangered Cottontail

There are 714 endangered animals in the United States, 287 of them native to California.  Ranging from one to two pounds and roughly a foot long, the Riparian Brush Rabbit is high on the list of endangered species in the state of California. They can be found on the west coast, from Oregon and all the way down to Mexico, scuttling away into burrows and climbing trees in temperate and arid climate zones. With their gray backs, white bellies, and relatively small cotton tails, the Riparian Brush Rabbits occupy thickets of willows, wild rose bushes, blackberry, coyote bushes and wild grape vines. While green clover is their favorite source of sustenance, they also enjoy munching on other grasses, shoots, and leaves. They’re a rather secretive creature, that is, when they’re not sunbathing on a warm day.

The Riparian brush rabbit was officially listed as “endangered” under the Endangered Species Act in 2000. Their rough population estimate is unknown, though the great decline in numbers can be attributed to a wide range of threats. 

A large percentage of the species lives in the San Joaquin Valley in Central California, where their habitats are constantly being fragmented, flooded, and degraded by vegetation removal. As opposed to natural predation and competition, illegal hunting is one of the anthropogenic causes for the rabbit’s decreased population size. Similarly, toxic rodenticides were used on Californian agricultural landscapes to control ground squirrels and other animals who burrow into water conveyance structures. Riparian brush rabbits took a hit as rodenticides hindered their ability to disperse from their protected regions and mingle with other populations outside their range. Gene flow is crucial to having high survival rates, as it increases genetic diversity and allows for healthier mating sprees. As lands in the central Valley get more and more fragmented, populations of riparian brush rabbits will be forced to reside in more isolated communities.

Climate change is the largest anthropogenic cause of this species’ hardships. Generally, as weather patterns have shifted over time, rainfall events have become less consistent and more extreme. This has led to more floods in addition to the occurrences of severe droughts. The rabbit’s habitat does not provide subsequent vegetation to act as coverage during a flood. With the rise of suburban development and cities’ anti-flood architecture, the impact floods will have on riparian brush rabbits is projected to increase, as more of the water during high-pressure weather events will flow towards undeveloped brush regions.  It is expected that local populations will crash time and time again. The fate of the species heavily relies on the success of rabbit numbers in areas that are less susceptible to flooding.

As many in California are probably aware, climate change has also affected the rate and magnitude of wildfires. The scorching flames burning on the Interstate 15 are just the tip of the iceberg. Average sea levels in the San Francisco Bay Area are expected to rise 0.30-0.45m by 2050, and temperatures expected to shift by an increase of 2.0-3.0 degrees Celsius. Rising temperatures will challenge the riparian brush rabbit’s ability to survive in an extremely hot environment. Additionally, 80% of California's largest fires in history have burned in the past decade.  Property damage is increasing, not just for us, but riparians brush rabbits and other forms of life in affected areas. Wildfires threaten the species with its force of mortality as well as the destruction of habitat. The scale at which they directly hurt population numbers is currently small, though it will only increase substantially as climate change thresholds are met as time goes on.

The strategy to avoid the potential of this endangered species generally points towards increased management of vegetation and wildlife. In 1998, the riparian brush rabbit was included in  the Recovery plan for the upland species of the San Joaquin Valley, California. Safe areas, or refugia, are currently being built to protect the rabbits from future floods. Conservationists are working with private landowners to broaden habitat land in order to execute the release of captive bred individuals successfully. Since riparian brush rabbits only produce nine to sixteen offspring (or “kittens”) annually, breeding projects are necessary at this stage to keep the populations afloat. The San Joaquin Valley Wildlife Refuge is a prime example of what expansive conservation efforts can do. Formerly used as agricultural land, the Refuge has been restored with native vegetation such as Fremont cottonwood, coyote bush, blue elderberry, and black willow. After just a few years of richer biomass, bunny mounds had grown ten feet higher, and the riparian brush rabbits have become more equipped to protect themselves from potential flood events. However prosperous the rabbit population is in this example, it does not diminish the fact that this species is on the edge of extinction. It is crucial that the riparian brush rabbit remains on the Endangered Species List, for they need all the attention they can get to keep their heads above anthropogenic troubles.