Squirrel Middens Influence Marten Use of Subnivean Access Points

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American Midland Naturalist



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Martens (Martes americana) use the subnivean zone during winter to obtain prey. In Yellowstone National Park, we noted that martens used access holes differentially, and that a number of subnivean access holes were associated with red squirrel (Tamiasciurus hudsonicus) middens. In this paper we address the question: Does the presence of red squirrel middens influence subnivean access point use by marten? Marten use of access points was influenced significantly by presence of middens. Thirty-three percent of used access points were associated with middens compared to 16% for unused access points (Kendall's tau t = -0.2293, P = 0.015). Martens appeared to key in on subnivean prey and used access holes with higher small mammal biomass (not including squirrels) more frequently (t-test t = -3.0697, df = 88, P = 0.002). When squirrels were included in the analysis, the relationship was strengthened (t-test t = -3.9723, df = 88, P = 0.0001). Scat analyses (n = 69) identified red-backed voles (Clethrionomys gapperi, 35.5%), red squirrel (21.1%), unknown sciurids (9.0%; total sciurids 30.1%) and lagomorphs (16.6%) as the major prey species. Coarse woody debris (CWD) levels around access holes did not differ regardless of whether squirrel middens were present or absent (t-test t = 0.1363, df = 88, P = 0.89). Likewise small mammal biomass levels did not differ whether middens were present or absent (t-test t = 0.9771, df = 88, P = 0.33). Access use was not related to percentage CWD when tested using a separate (unequal) variance estimate t-test (t-test t = -1.5959, df = 88, P = 0.11).

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