Home range size and habitat selection of reintroduced Sylvilagus bachmani riparius

Effective restoration of threatened or endangered species requires understanding of basic ecological requirements such as habitat selection and home range needs. The endangered riparian brush rabbit (Sylvilagus bachmani riparius) occupies areas of dense, brushy cover along streamside communities in the San Joaquin Valley of California, but over 93% of this habitat has been lost to urban and agricultural development. We released over 325 captive-born rabbits at the San Joaquin River National Wildlife Refuge (Refuge) between July 2002 and July 2005, and we monitored 312 of these rabbits via radiotelemetry to assess spatial and habitat selection. Home ranges and core areas were similar among males and females, and were larger in the breeding season than during the nonbreeding season. Perhaps reflecting a growing population, home range estimates decreased in size over the duration of the study Animals moved in response to a wildfire in July 2004, but home range area was similar in 90-day pre- and postfire periods. Of 1,143 possible dyads, 534 (47%) exhibited a mean of 86% overlap in 95% fixed-kernel home ranges. Overlap did not differ by dyad type (e.g., male male), but was greater in nonbreeding than in breeding seasons; unlike home ranges, we did not detect any temporal changes in overlap as might be expected in a growing population. Riparian brush rabbits exhibit scale-independent habitat selection, disproportionately favoring thick understory cover such as sandbar willow mixed with dense shrubs (blackberry, roses). Refuge managers have promoted escape cover and flood refugia at strategic locations throughout the Refuge; our results concur that these are important habitat elements in the niche of riparian brush rabbits.