The status of ship rats Rattus rattus on the Shiant Islands, Outer Hebrides, Scotland

Ship rats Rattus rattus are amongst the rarest mammals in Britain and yet they are officially classified as pests. They exist independently of contemporary human settlement at only two sites both of which are important seabird breeding colonies. There may be a conflict between conserving this rare species while ensuring the welfare of seabirds. We present a case study of the potential conservation dilemma of ship rat management on the Shiant Islands. Using capture-mark-recapture the pre-breeding rat population in May 1996 was estimated to be between 230 and 400. Evidence of rat predation on eggs and chicks was scarce at the time of our survey. The small number of rats was not thought to have a substantial effect on the nesting success of the comparatively large seabird populations. We suggest that the scientific interest of the rat population may outweigh the conservation needs of the seabirds and that formal control measures are currently unwarranted.