Grays Lake Ecosystem. Comparison of Wetland and Upland Management Practices at Grays Lake National Wildlife Refuge ? Small Mammal Populations

Authors(s): J. Austin

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Publication Date: 0000-00-00

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Abstract: Small mammals are an important part of the wet meadow and grassland communities because they are an important prey for avian and mammalian predators (including sandhill cranes) as well as being consumers of both plants and invertebrates. The objective of this component is to determine small mammal responses (abundance) to three wet meadow management regimes (idle, grazing, and burning). Because effects due to singular treatments are likely to be more easily interpreted than effects due to the rotation treatment during the short duration of this study, indices to small mammal abundance were estimated only in response to idle, burn, and graze treatments. This late-summer survey provided an index of small mammal response to growing-season habitat under management treatments, and also provided supplemental information on diversity of small mammals in treatment units. To avoid disturbance to nesting birds, we limited our capture efforts to late summer. Small mammals were trapped in late July-early August using Sherman live-traps. Field personnel follow guidelines for trapping and handling mammals established by the American Society of Mammalogists (1987). Traps were located in runway depressions or adjacent to clumps of vegetation that afford temperature moderation and shade. Traps were checked twice each day, in the early morning and late afternoon, to minimize the time animals will be in the traps. Animals were released unharmed at the site of capture, although shrews tend survive poorly, even when live-trapped, because of their very high metabolism. Data collected at each trap site included species of animal captured (if any), site dampness (saturated, damp, dry), vegetation characteristics (amount of green or dead vegetation), and litter abundance. The abundance estimate for each species in a unit was expressed as rate of captures per 100 trap efforts. We captured 5 species: montane vole (Microtus montanus; n=1079), meadow vole (Microtus pennsylvanicus; n=324), deer mouse (Peromyscus maniculata; n=28), vagrant shrew (Sorex vagrans; n=98), and least weasel or ermine (Mustela erminea; n=98). Capture rates of small mammals increased markedly between 1997 and 1998, primarily due to the irruption of montane voles, and to a lesser extent meadow voles. Capture rates of montane voles increased from 0.611 to 5.0 captures/100 trap efforts, and that for meadow voles increased from 0.42 to 0.87 captures/100 trap efforts. In 1999, vole populations crashed to 0.13 and 0.29 captures/100 trap efforts, respectively, and recovered somewhat by 2000. In contrast, capture rates for ermine increased from 0.05 in 1997 to 0.150 in 1999 then declined suddently in 2000 to 0.367 captures/100 trap efforts. Data analyses indicated strong year effects, but no effects of habitat management treatments or, more most species, effects of litter, vegetation, or soil wetness. Capture rates for all species except ermine were highest in 1998. Deer mice, captured only in 1998 and 2000, were most commonly found in 1998 on damp soils. For ermine, annual differences in capture rates were detected only on saturated sites; indeed over all years, ermine capture rates were much higher on saturated sites than on damp or dry sites. Our results did not indicate that the habitat treatments used in this study affected small mammal populations. Rather, year effects dominated. The irruption of montane voles probably is linked to relatively high precipitation and plant growth during summer 1997, which would promote high reproduction and overwinter survival in voles. We speculate that the high microtine populations present during 1998 provided an abundance of alternative prey for ermine, fox, skunk, buteos, and other predators in the Grays Lake basin that year, and thus contributed to the higher nest success for a number of ground-nesting birds.

Keywords: Gray's Lake, Idaho, animal, mammal, habitat, predation, bird, Aves, ornithology, crane, sandhill crane, Anatidae, waterfowl, water bird, food, forage, management, grazing, fire, nest, nesting, trapping, Sorex, Soricidae, shrew, vole, Muridae, Cricetidae, montane vole, Microtus montanus, meadow vole, Microtus pennsylvanicus, insectivore, shrew, vagrant shrew, Sorex vagrans, mouse, deer mouse, Peromyscus maniculata, least weasel, weasel, ermine, Mustela erminea, Mustelidae, Mustela nivalis, predation, fox, Vulpes vulpes, skunk, Mephetis mephitis, Buteo, hawk