PARENT SESSION

RECONSIDERING THE CHARACTERISTICS OF OPTIMAL HABITAT FOR THE ENDANGERED RIPARIAN BRUSH RABBIT. Matthew R. Lloyd, Daniel F. Williams and Patrick A. Kelly. Endangered Species Recovery Program, California State University, Stanislaus, 801 W. Monte Vista Ave., Turlock, CA, USA.

ABSTRACT- Until 2001, the only known populations of riparian brush rabbits (Sylvilagus bachmani riparius) and riparian woodrats (Neotoma fuscipes riparia) occurred within Caswell Memorial State Park (MSP), near Ripon, California. Since brush rabbits and woodrats typically co-exist, it was believed that these species possess similar habitat requirements derived from Caswell MSP's predominately climax riparian oak woodland. However, annual monitoring of the brush rabbit and woodrat populations at Caswell MSP, along with subsequent discoveries of additional brush rabbit and woodrat populations, indicate that Caswell MSP may not provide optimal habitat for riparian brush rabbits. Baseline monitoring of both species occurred at Caswell MSP in 1993, and annual monitoring has been conducted since 1997, when the park experienced extensive flooding. Since 1997, capture rates of brush rabbits at three locations within Caswell MSP have fluctuated, but have not increased to the baseline capture rates, whereas capture rates of woodrats have steadily increased and surpassed baseline levels. During 2001-2004, capture rates of riparian brush rabbits in the South Delta region of Central California were 4-12 times greater than at Caswell MSP during 2001-2004. Brush rabbit habitat in the South Delta is frequently disturbed by human activity, and is dominated by early-mid successional riparian vegetation. Due to the Caswell MSP's distinction as the only protected habitat for riparian brush rabbits and riparian woodrats, it is imperative that it can permanently provide suitable habitat for both species–vegetation management must incorporate the needs of both. This likely will entail creating and maintaining a mosaic of early successional to climax riparian woodland habitat.

KEY WORDS: rabbit, riparian, sylvilagus bachmani riparius, endangered species