Physical exclusion of non-target species in tunnel-trapping of mammalian pests.
We developed and tested physical excluders to prevent non-target animals from entering tunnels containing spring traps intended to kill a range of small (<2 kg) mammalian pest species. In field trials over 82,954 trap-nights, excluders did not significantly decrease stoat (Mustela erminea) or weasel (Mustela nivalis) capture rates, but did substantially reduce the capture rate of larger target species, notably grey squirrels (Sciurus carolinensis) and rats (Rattus norvegicus). Excluders virtually eliminated capture of hedgehogs (Erinaceus europaeus) - a legally protected species. By inference, larger protected species (polecat Mustela putorius, pine marten Martes Martes, otter Lutra lutra and wild cat Felis sylvestris) would be excluded, as would mink (Mustela vison), a legitimate target species. These excluders should be advocated where there is a real risk of catching protected species. However, because excluders compromise utility, we recommend that their use should remain discretional unless clearly preferable alternative methods to manage target pest species are developed.