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85 Percent of Captures 40 highway n=126 powerline n=161 results also suggest that the effect of road proximity differs by 30 species. When the percentage composition they report for deer mice is converted to absolute numbers, abundance was 20 consistently higher near interstate than county highways. 10 Whether this phenomenon was related to the larger area of 0 grassy habitat along interstate highways is not clear, but it ROW 50 300 600 does suggest that large highway size and volume did not have Transect an overwhelmingly negative effect on deer mice. In keeping Note: Data adjusted for realized trap effort and non-availability of traps due to the capture of other species. with that observation, the research team found no consistent regional patterns of deer mouse abundance in relation to dis- Figure 27. Distribution of deer mouse captures among transects for each treatment. tance from highway. The only other species reported by Adams and Geis2 that had more than one capture in the British Columbia study area was the meadow vole, for which habitat. This observation suggests a strongly uneven distribu- there was a general tendency to be more common closer to tion, and the likelihood that the greater abundance at the roads, but no consistent pattern with respect to highway size. transmission-line sites was a chance effect. Geographically closer to the British Columbia study area was Deer mice provide a better opportunity to compare trans- the field site of Mills and Conrey170 in northwestern Montana. mission-line ROW to highway ROW transects, given this In forested habitat adjacent to the ROW of two 2-lane high- species employs very broad habitat-use patterns and distribu- ways, southern red-backed vole abundance was greater on a tion.178 It was also typically abundant in the samples for this trapping grid close to the highway at one site but greater on a study. There were no observed differences between transmis- grid distant from the highway at the other site. Deer mice and sion-line and highway ROW samples for deer mouse abun- chipmunks (combining yellow-pine chipmunks and red- dance, sex ratio, and male weight or female weight. There was, tailed chipmunks [Tamias ruficaudis]) appeared to be mar- however, a weak suggestion of a greater proportion of juveniles ginally more abundant on the grids nearest to the highways. in the sample on the highway site. The latter observation could At a site along a four-lane highway, rodent abundance on a be taken to be indicative of a highway effect, with juveniles trapping grid straddling the ROW-forest boundary was com- perhaps being displaced to lower quality habitat or alterna- pared to a second grid farther from the highway and entirely tively having higher survivorship. Still, there was evidence of in the forest. In that case, deer mice were more abundant near differences among treatments at the 600 m transect for deer the highway, whereas red-backed voles and chipmunks were mouse abundance, as well as male weight and sex ratio. It would most abundant farther from the highway. Those results are be extremely unlikely that a highway effect would be evident consistent with a simple preference for open habitats by deer at the 600 m transect without being obvious at the 300 m, mice and for forest by red-backed voles and chipmunks, 50 m, and ROW transects. This observation suggests a high which is consistent with the results of this study. likelihood of any differences between treatments in deer mouse variables being related at least as much to chance, microhabi- Interpretation, Appraisal, and Applications tat, or other localized effects as to the presence of the highway. Adams and Geis2 conducted similar research in the south- In Utah, the research team recorded higher abundance and eastern, midwestern, and northwestern United States. Their density further from the road in 2004, and higher diversity and Females Males highway n=46 powerline n=53 highway n=36 powerline n=57 25 25 Adult Mean Weight (g) Adult Mean Weight (g) 20 20 15 15 10 10 5 5 0 0 ROW 50 300 600 ROW 50 300 600 Transect Transect Figure 28. Weights of adult deer mice, compared among transects for each treatment.