Unique and Rare - Catalina Island Conservancy

Island Raritycontinued from page 1D. KnappCase Study #1The Santa Catalina Island ShrewWeighing little more than a penny, the Santa CatalinaIsland Shrew (Sorex ornatus willetti) is believed to bethe rarest mammal on Catalina. A subspecies of themainland ornate shrew, this tiny insectivore occurs onlyon Santa Catalina Island. Very little information existsabout its life history, abundance, and distributiondespite several attempts to study it over the past twodecades.The Catalina Mahogany occurs naturally in only one remotegully on the southwest side of the island.suppression appears to be a factor in the rarity of someof our plant species, such as the Island Tree Poppy(Dendromecon harfordii) and Felt-leaf Ceanothus(Ceanothus arboreus).We have also introduced many non-native and invasiveplant and animal species. Introduced animals such asferal pigs (Sus scrofa) and bullfrogs (Rana catesbeiana )threaten rare native species on Catalina such as theTwo-striped Garter Snake (Thamnophis hammondii)through habitat destruction and predation. In addition,it has been estimated that up to 32 of Catalina’s nativeplant species have been eliminated from the island ordrastically reduced due to the impacts of non-nativeherbivores (Thorne 1976). Introduced animals such asMule Deer (Odocoileus hemionus californicus) and feralpigs hinder oak production by browsing the younggrowth, disturbing the soil, and foraging on acorns.Invasive annual grasses such as Bromes (Bromus spp.)and Wild Oats (Avena spp.) also reduce oak seedlinggrowth through crowding and water competition.Without the crucial replacement of aging oak trees,Catalina’s landscape could look significantly different inthe future as the oaks die off and there are none toreplace them.Between 1941, when it was first described, and 2002,the Santa Catalina Island Shrew had only been seen anddocumented a total of seven times from Avalon,Middle, and Cottonwood Canyons. Since February 2002,monthly monitoring of reptiles, amphibians, smallmammals, and invertebrates using permanently placedpitfall trap arrays has led to the capture of twoadditional shrews in Cottonwood Canyon. Recently anintensive study was conducted by the Conservancy todetermine the distribution and abundance of shrews inthis canyon. More than 10,500 trap nights of effortusing pitfall and live-traps were necessary to capturejust three additional individuals of this rare shrewsubspecies. Although notoriously difficult to trap,similar studies on the mainland capture more far moreshrews per effort.The endemic Santa Catalina Island Fox is found on SantaCatalina Island and nowhere else.F. StarkeyIt is important to understand the causes of rarity to beable to develop conservation strategies that reduce thelikelihood of a rare species going extinct in the future.Through research, restoration of natural ecologicalprocesses, and removal of threats such as invasive plantsand animals, the Catalina Island Conservancy is helpingto protect the rare and unique plant and animal speciesof Santa Catalina Island. The help of the localcommunity and visitors is critical to our success.Like past accounts, these most recent sightings suggestthat the Santa Catalina Island Shrew may be closelyassociated with riparian and wetland habitats. Thesehabitats provide low, dense vegetation and heavy leaflitter with high insect densities, cover for nesting andforaging, and protection from predators (such as cats,foxes, owls, and snakes). Unfortunately, wet habitatsPlease see page 4Conservancy Times3