A butterfly at risk from pesticides and a plant potentially targeted by collectors are B.C.'s newest endangered species, according to an annual assessment by the Committee on the Status of Endangered Wildlife in Canada released Monday.

The Oregon branded skipper inhabits sparsely vegetated at-risk Garry Oak and coastal sandspit ecosystems and is found in only four of 16 fragmented sites totalling less than 16 square kilometres. It is threatened by the application of Btk pesticide used to control the invasive gypsy moth and by the encroachment of vegetation in open habitats.

Also endangered is Tweedy's Lewisia, a showy perennial plant that exists in two small sub-populations and has undergone a decline of up to 30 per cent in recent years, possibly due to plant collecting. The small population size and potential impact from climate change also put the species at risk.

COSEWIC also gave a threatened status to Audouin's night-stalking tiger beetle, which is restricted to a narrow strip of coastal lowland around Boundary Bay and Greater Victoria. Major threats include habitat loss through agricultural and urban development, vegetation succession in open habitats, disturbance from recreational activities, and, in the longer term, sea level rise. The flightless beetle is known to occur in fewer than 10 known sites, and the discovery of more populations is unlikely.

The western waterfan is also considered a species of special concern. The lichen, known to occur in only five sites in B.C., grows at or below water level in clear, permanent, unshaded alpine or subalpine streams. Habitat loss is likely to result from temperature increases caused by climate change. Also, increasing drought will transform permanent watercourses into ephemeral streams.

Meanwhile, the status of wood bison has been downgraded to special concern from threatened due to growing numbers, which are thought to total up to about 7,100 mature animals. The Rocky Mountain tailed frog is downgraded to threatened from endangered due to increased protection in the Flathead River.

COSEWIC is a national body of scientists which makes recommendations to the federal government for listing of wildlife for legal protection and recovery under the Species At Risk Act. COSEWIC recommendations are based on science and both community and traditional aboriginal knowledge but do not account for political, social or economic factors.

lpynn@vancouversun.com