Modify culverts to make them more accessible to mammals
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Culverts under roads may be used as crossing routes by mammals. This use reduces collision-associated risks to mammals and to motorists compared with crossings over the road surface. Some culverts may be less suited as crossing routes than others. For example, culverts with water flowing across their entire width may not be used by some mammals whilst tunnel length may also be a barrier to their use. A range of modifications can be made to try to increase culvert suitability for use by wild mammals.
Supporting evidence from individual studies
A replicated, site comparison study in 1997–1999 in dry shrubland along a highway in Texas, USA (Cain et al. 2003) found that modified culverts were used more by bobcats Lynx rufus than were unmodified culverts. Use of crossings by cat spp. was higher at modified culverts (2.6 visits/month) than at unmodified culverts (0.5 visits/month). The rate of crossings at bridges (2.2 visits/month) was similar to that at modified culverts. Most cats recorded were bobcats, which accounted for 371 of 471 camera-trap images obtained at culvert entrances. Remaining images were of feral cats Felis catus. Five modified culverts, nine unmodified culverts and four bridges were monitored. Modified culverts had elevated central catwalks (to facilitate a dry crossing even when water was flowing through), open-air sections at the road centre (but fenced, to prevent escape at this part) and enlarged entrances. Crossings were checked two times/week from 1 July 1997 to 31 May 1999 for tracks. Remote cameras were used at seven crossings at a time, from 1 August 1997 to 31 May 1999, and were rotated among all crossings.Study and other actions tested