No abstract

The riparian brush rabbit (Sylvilagus bachmani riparius) is an endangered species found in dense, brushy habitat in the California's Central Valley. We implemented a reintroduction program to bolster populations at a Federal Wildlife Refuge and to assess factors influencing mortality and subsequent survival of released individuals. Between July 2002 and July 2005, we reintroduced 325 captive-bred individuals to unoccupied habitat within their historic range using a soft-release strategy and monitored their subsequent survival with radiotelemetry. Longer time in soft-release pens resulted in increased monthly survival. Rabbits were most susceptible to post-release mortality during the first 4 weeks following reintroduction and both body mass and length of time in the soft-release enclosure influenced this relationship. When we controlled for release mortality during this acclimation period, subsequent monthly survival probabilities were most strongly influenced by release year (year 1 vs. years 2 and 3) and by a catastrophic flooding event; length of time in the soft-release enclosure remained an important variable in longer-term survival. Cause of mortality was unknown for the majority of deaths (61.9%), but predation (including presumptive predation) was the greatest known cause of death in translocated rabbits (26.4%). Reintroduction programs should employ an adaptive management approach with ongoing monitoring of target animals and concurrent analysis to allow managers to adjust methods as conditions dictate.

No abstract

Expanding habitat protection is a common tactic for species conservation. When unprotected habitat is privately owned, decisions must be made about which areas to protect by

This review describes the great diversity and endemism of Kangaroo Rats Dipodomys spp. in California. Many species are formally listed as endangered and others are likely to be listed in the near future. We review recent efforts to conserve these small bipedal rodents. We argue that they deserve special emphasis because they have been shown to play key roles in ecosystem structure and composition. Indeed, many of the plant communities occupied by Kangaroo Rats have now been identified as at risk because of excessive habitat destruction and fragmentation. It is clear that preservation of Kangaroo Rats and their plant communities will not be achieved through simply setting aside blocks of habitat as reserves. Conservation areas will require active management in order to maintain existing biodiversity, but further studies are required to ascertain how best to manage these communities. We believe that Kangaroo Rats are important subjects for management studies and ecosystem monitoring. Preliminary studies of the size of reserves required to maintain viable populations of one species show that despite the often high abundance of Kangaroo Rats (35 animals/ha), large areas (>5 000 ha) will be required. Therefore, considerable biodiversity is likely to be protected by focusing on these species, particularly if conservation and recovery efforts are applied on a regional scale.