Small‐Mammal Microhabitat Associations and Response to Grazing in Oregon

Abstract

Livestock grazing is common and widespread throughout North America, yet few studies have evaluated its effects on small mammals. We studied small mammals in mixed‐conifer forests and oak woodlands on the Cascade‐Siskiyou National Monument in southern Oregon, USA, to 1) evaluate small‐mammal microhabitat associations, 2) identify riparian‐associated species, and 3) test the hypothesis that grazing does not influence small mammals after accounting for microhabitat associations. We live‐trapped small mammals at 16 study sites and used logistic regression to model probability of capture on measured habitat characteristics at each trap station and to evaluate effects of grazing. Over 2 years, we trapped 1,270 individual small mammals representing 18 species. Odds of capturing western harvest mice (Reithrodontomys megalotis), dusky‐footed woodrats (Neotoma fuscipes), and long‐tailed voles (Microtus longicaudus) were lower (P < 0.05) on heavily versus lightly grazed sites. Odds of capture for deer mice (Peromyscus maniculatus) were lower (P < 0.05) on heavily versus lightly grazed sites in woodlands, but there was less difference in the odds of capture between grazing intensities in conifer forests. Odds of capturing Townsend's vole (Microtus townsendii) were lower on heavily versus lightly grazed riparian areas. Western harvest mice, long‐tailed voles, and Townsend's voles were associated with, but not obligated to, riparian areas. Deer mice were ubiquitous, but captures were also higher (P < 0.05) in riparian areas compared with uplands. Siskiyou chipmunks (Tamias siskiyou) and piñon mice (Peromyscus truei) were associated with uplands (P < 0.05) rather than riparian areas. Trowbridge's shrews (Sorex trowbridgii), Siskiyou chipmunks, and bushy‐tailed woodrats (Neotoma cinerea) were positively associated with coarse woody debris. Land managers should anticipate that small mammals associated with herbaceous or shrub cover, particularly in riparian areas, will decline when cattle remove this cover.

Influence of repeated fertilization and cattle grazing on forest ecosystems: Abundance and diversity of forest-floor small mammals

“…Contrary to the mixed responses of small mammals to increases in vegetative or other resource productivity levels, livestock disturbance appeared to have a consistently significant negative impact on small mammal abundance (Grant et al, 1982;Bock et al, 1994;Hayward et al, 1997;Chapman and Ribic, 2002;Johnston and Anthony, 2008) and species richness or diversity (Reynolds and Trost, 1980;Medin and Clary, 1989;Giuliano and Homyack, 2004). Again, as with the productivity-diversity studies, variable results based on scale of habitat measurements (Rosenstock, 1996) and generalist vs. specialist species of small mammals (Schulz and Leininger, 1991) were also reported.…”

“…5a). The one peak population in 1997 at the heavily grazed fertilized stands suggested that grazing by cattle and the consequent reduction in vegetative cover of herbs and grasses, even in fertilized stands, may inhibit abundance and hence population fluctuations in Microtus (Grant et al, 1982;Chapman and Ribic, 2002;Evans et al, 2006;Johnston and Anthony, 2008;Sullivan et al, 2012).…”

Woody debris, voles, and trees: Influence of habitat structures (piles and windrows) on long-tailed vole populations and feeding damage

“…This dramatic difference has two likely explanations. Firstly, cattle grazing on summer range was present on our sites in all years, immediately postharvest, and likely contributed to a reduction in herbaceous food and cover for voles (Johnston and Anthony, 2008). Secondly, our CWD structures seemed to provide a suitable moist microclimate (Getz, 1985), sufficient cover, and likely some fungal sporocarps and coniferous seeds as food sources.…”

Small mammal responses to moose supplementary winter feeding

“…Several studies have investigated the effects of large herbivore densities on small mammals, and most of these report negative effects (Keesing and Crawford 2001;Keesing 1998;Johnston and Anthony 2008;Saetnan and Skarpe 2006;Buesching et al 2011). However, there are few studies investigating effects of supplementary feeding of large herbivores on small mammals (but see Moseley et al 2011).…”