Effects of tropical rainforest roads on small mammals: inhibition of crossing movements

Along a narrow, unsealed road through rainforest in north-eastern Queensland, movements of small mammals were examined to determine whether the road would inhibit road crossings, thereby causing linear barrier effects. Crossings of a 12- or 20-m-wide road clearing by Melomys cervinipes were severely inhibited, crossing inhibition of Rattus sp. was less severe, while crossings by Uromys caudimaculatus were unaffected. This differential effect was attributed to species differences in size, mobility and behaviour. Baiting on only one side of the road increased crossing rates for all species. During the breeding season, crossings of 20-m clearings by Rattus sp. were almost completely inhibited and were significantly fewer than crossings of 12-m clearings. Clearing width had little effect on crossing rate outside the breeding season. Seasonal dispersal of juvenile and breeding animals appeared to explain this discrepancy in clearing-width effects. Rattus sp. were significantly less likely to cross a road where there was no vegetative cover at the entrance to a road culvert than where there was cover at both culvert entrances. Linear barrier effects for small mammals may be mitigated by narrower road-clearing widths, by replanting of grassy road verges resulting in increased cover at culvert entrances and canopy closure above the road, and by providing more faunal underpasses.