The San Joaquin Riparian Bush Rabbit By David Murray

Image: https://www.kcet.org/redefine/states-most-endangered-mammal-gains-ground-in-delta

The Riparian Bush Rabbit & Habitat in the San Joaquin Valley

            The Riparian Bush Rabbit, RBR, is located along the Pacific coast of the United States and stretches down to the furthest part of Baja California. The link shows the total area that the species can occupy according to the International Union for Conservation of Nature (the IUCN): http://maps.iucnredlist.org/map.html?id=41302. According to the IUCN the RBR is a part of the Animalia kingdom, Chordata phylum, Mammalia class, Lagmorpha order, and Leporidae family. Its name in Spanish is Conejo Matorralero and its scientific name is Sylvilagus bachmani, the San Joaquin is home to the subspecies Sylvilagus bachmani riparius. The RBR lives in clumps of bramble and brush, the size of which dictate the number of rabbits which can live within it and how far the rabbit will travel away from its home. It does not burrow but rather nests among the plants. Riparian means that it is situated in land adjacent to rivers and streams, in the San Joaquin the rabbit specifically stays close to lots of vegetation such as rose bushes, blackberry bushes, and willows. Breeding season for the rabbits varies based on where it lives but litters tend to yield two to four rabbits, in California the season begins in December but in Oregon it begins in February. Both locations have mating seasons that last for about six months in length, California ending in May and Oregon ending in August. The main food source of the RBR is grasses but it will eat other plants as the seasons make them available.

The San Joaquin Delta and Valley over Time

Image: https://www.epa.go

Pristine San Joaquin Delta, when it was first discovered, was full of waterways and riparian forests. There was an abundance of wildlife and fertile land that flooded every so often making it look for like a lake than rivers and streams. As people have started to move into not only the San Joaquin Valley but also other areas of California including Southern California, the waterways have dramatically been changed. This was first through many levees that provide defined waterways and prevent flooding over the agricultural lands that now dominate the delta. The Caswell Memorial State Park in the valley is still subject to flooding which has gotten worse with the increase of levees among the agricultural fields. This park is the main area in which the RBR lives, the habitual amount of the park for the rabbit is roughly 200 acres. Next was the movement of people into the valley which greatly decreased the natural habitat of the RBR, according to the IUCN the riparian habitats have been reduced to one percent of their historical areas. A full report on the change of the San Joaquin can be found at https://pubs.usgs.gov/circ/circ1182/pdf/11Delta.pdf. The IUCN also reported that in 1993 there was roughly 241 rabbits at Caswell Memorial State Park but according to capture and release methods to measure population size between 1997 and 2004 the population had decreased by seventy-three percent.

The Listing

            The Riparian Bush Rabbit (Sylvilagus bachmani riparius) was put on the endangered species list by the US Fish and Wildlife Service on February 23, 2003. The state of California put the RBR on its endangered species list in May of 1994. The lead location in this development was in California and Nevada but has now escalated to anywhere it is found. The RBR is listed as endangered.

Reasons of Listing and Continuous Threats

            The first threat of the RBR was the movement of humans into the valley. They converted riparian land into agricultural fields, fragmented more habitat by creating levees to deal with flooding, and started to build homes. All of these greatly decreased the rabbits’ natural habitat to roughly one percent of its historical size. On top of this the rabbits natural breeding season is not year round but roughly lasts for six month spans. Unfortunately roughly one of six RBR babes will make it to their first birthday.

            Currently the largest threat to the RBR is the flooding of the valley. This pushes the rabbit, who naturally does not travel more than a few feet from its home, out into the open. In the 1970’s, according to a report from KCET (https://www.kcet.org/redefine/states-most-endangered-mammal-gains-ground-in-delta), the flooding of Caswell State Memorial Park was so bad park rangers used boats to travel through the riparian woods and save the rabbits who had climbed up trees in order to avoid being drowned. The next largest threat is the degradation and destruction of their habitat for agriculture and neighborhood/commercial development. The development of levees and fields for agriculture has basically trapped the RBR in the Caswell State Memorial Park. After this threat is the increase in cats and dogs from the influx of housing communities in the valley. This greatly affects the small populations of rabbits located outside of Caswell because they have such small numbers.  

Recovery Plan

            The species receives the typical protection of a state park as most of its populations are located in the Caswell State Memorial Park. Repeated studies of the population size within the park are funded as to monitor the state of the species. The CA Department of Parks and Recreation has increased its fire trails which actually provides more edge habitat for the species. The department is also improving its methods of fighting feral animals to make their efforts more sensitive to the rabbit. On top of this they also are planning to help increase the protection of all species located within Caswell. A plan was also developed to move a small population the banks of the Kings River in Fresno but so far this has not been implemented. Captive breeding of the rabbit started in 2001 (https://www.fws.gov/sacramento/es/recovery-planning/Riparian-Brush-Rabbits/es_recovery_rip-brush-rabbit-recovery.htm) in order to try and help increase the population size.

What can we do?

            There is a limited amount we can actually do for the species. Restoring its natural habitat would mean destroying vital agricultural fields and diverting water headed for Southern Californians consumption. One important thing is to keep the predation from house pets and natural predators down among Caswell borders. Another possible way to help is by creating habitats that connect with Caswell, possibly by creating habitat bridges, which would increase the area accessible to the rabbit. This would provide an opportunity for the rabbit to spread through more of the San Joaquin.

Some Resources

Clarke, Chris. (8 July 2015). “State's Most-Endangered Mammal Gains Ground in Delta.” KCET.

Accessed 27 Novr 2016.   

U.S. Fish and Wildlife Service. 1998. Recovery plan for upland species of the San Joaquin

Valley, California. Region 1, Portland, OR. p. 164-9.

“Riparian Brush rabbit (Sylvilagus bachmani riparius).” U.S. Fish and Wildlife Service,

https://ecos.fws.gov/ecp0/profile/speciesProfile?spcode=A0DN. Accessed 27 Nov 2016.  

“Sylvilagus bachmani.” ITIS, http://www.iucnredlist.org/details/41302/0. Accessed 27 Nov

2016.

“San Joaquin Valley.” EPA, https://www.epa.gov/sanjoaquinvalley. Accessed 27 Nov 2016.  

“Riparian Brush Rabbit Recovery.” U.S. Fish and Wildlife Service,

https://www.fws.gov/sacramento/es/recovery-planning/Riparian-Brush-Rabbits/es_recovery_rip-brush-rabbit-recovery.htm. Accessed 27 Nov