Progress 07/01/03 to 06/30/04
Outputs
Mogollon voles (Microtus mogollensis) are found in grassy areas within ponderosa pine (Pinus ponderosa) forests. Monitoring grassland condition is an important issue facing forest managers. We evaluated the effectiveness of measuring Mogollon vole signs as a method to monitor Mogollon vole populations. We used 5 vole signs and a Vole Sign Index (VSI, a combined measure of the 5 signs) to examine relationships between vole capture rate, vole presence and vole sign. We conducted our study in 6 meadows (4 on the Kaibab and 2 on the Coconino National Forests) in northern Arizona. In each meadow, we compared 1 area with high to 1 area with low density of vole sign (n = 12 areas; 6 pairs). These meadows lacked perennial or seasonal water sources and were dominated by Arizona fescue (Festuca arizonica) and blue grama (Bouteloua gracilis). In each meadow, we established trapping grids of up to 150 traps (e.g., 5 x 10) on 5 m spacing. At each trap location, we searched for the
presence (= 1) or absence (= 0) of each of the following 5 vole signs: (1) runways, (2) fresh (not decomposing) vole droppings, (3) old (decomposing) vole droppings, (4) fresh (green) grass clippings, (5) old (not green) grass clippings. Thus, the VSI for each trap location ranged from 0 to 5 before it was standardized to a percentage. Immediately after collecting VSI, we live-trapped each meadow. We used linear regression to determine associations between VSI and Mogollon vole capture rate and logistic regression to investigate which vole sign(s) were best predictors of Mogollon vole presence. Relative abundance of voles was correlated with all vole signs (R more than or equal to 0.61, P less than or equal to .03). Relative density of fresh droppings was the best predictor of vole capture rate (r2adj = 0.61, P = 0.001). VSI was the best predictor of vole presence. To monitor Mogollon voles in meadows, resource managers could use VSI, or search for fresh fecal material on runways.
Impacts
Because of the large amount of public lands that are grazed, or proposed for forest management in Arizona and disappearing grasslands due to ponderosa pine encroachment, we think that the Mogollon vole is a good Management Indicator Species for Forest Service land managers to use in northern Arizona. The VSI method was effective in predicting vole presence and capture rate. The VSI method required minimal training and equipment. There are no risks to personnel (e.g., Hantavirus or plague exposure) or animals and the cost of the VSI method was lower than live trapping small mammals.
Publications
- Yarorough, R. F. 2005. Using Mogollon vole (Microtus mogollonensis) sign to predict Mogollon vole presence in northern Arizona. Thesis, Northern Arizona University, Flagstaff. Yarborough, R. F. and C. L. Chambers. Using Mogollon vole (Microtus mogollensis) sign to predict Mogollon vole capture rate or presence in northern Arizona (In preparation, to be submitted to The Southwestern Naturalist).
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Progress 01/01/03 to 12/31/03
Outputs
Grazing is a common disturbance in southwestern United States riparian systems, as livestock and elk (Cervus elaphus) tend to concentrate along ephemeral washes and associated moist meadows. Some wildlife species are mobile and can shift to more favorable habitat, small mammals may be negatively affected by grazing because of their limited ability for movement. We live trapped small mammals during 5 trapping sessions in 6 montane wet meadows in northern Arizona; 3 with and 3 without 2 to 4 ha ungulate exclosures. We captured 335 animals including 175 Mogollon voles (52percent of captures), 144 deer mice (42 percent of captures), 5 pinyon mice (P. truei), 5 Stephens woodrats (Neotoma stephensi), 2 brush mice (P. boylii), 2 golden mantled ground squirrels (Spermophilus lateralis), and 2 Merriams shrews (Sorex merriami). Highest percentage of Mogollon voles were capture(61percent)in Feb 2000; captures substantially decreased from 50 individuals/1000 TN in 2000 and to
2/1000 TN in June 2001 and also were low in 2002 (6/1000 TN). Highest capture rates in areas with 2.5 m tall exclosures (intended to exclude livestock and elk) during all trapping periods. Capture rate of deer mice was higher in areas with exclosures than without exclosures except in Jun 2002. In Feb 2000, we measured habitat variables to identify habitat correlates with Mogollon voles. Trap stations with the highest probability of capturing Mogollon voles had greater grass biomass and were farther from forest edges. We also measured densities of Mogollon vole runways at all sites. Runway densities in areas inside and outside exclosures averaged 1.52 m/m(squared) and 0.39 m/m(squared), respectively. Captures of Mogollon voles were highly correlated with runway densities (R = 0.89, P = 0.0001). To assess whether we could use runway density to determine Mogollon vole abundance, we evaluated the effectiveness of monitoring active and inactive Mogollon vole runways as a method to monitor
Mogollon vole populations. We used 5 Vole Sign Indices (VSI) to determine relationships between capture rate and vole sign. We conducted our study in 6 upland, dry meadows (4 on the Kaibab and 2 on the Coconino National Forests) in northern Arizona. These meadows lacked perennial or seasonal water sources and were dominated by Arizona fescue (Festuca arizonica). In each meadow, we established trapping grids of up to 150 traps (e.g., 5 x 10) on 5 m spacing. At each trap location, we searched a 25 x 25 cm quadrat for the presence (= 1) or absence (= 0) of each of the following 5 vole signs: (1) runways, (2) fresh (not decomposing) vole droppings, (3) old (decomposing) vole droppings, (4) fresh (green) heaps of grass clippings, (5) old (not green) heaps of grass clippings. Thus, scores for each of the above vole sign indices (VSI) ranged from 0 to 5. Immediately after collecting VSI, we live trapped each meadow to relate VSI scores at each grid to the relative abundance of voles. We used
linear regression to determine associations between VSI for Mogollon voles and Mogollon vole relative abundance. Highest relative abundance of voles was correlated most strongly with runway density and dry grass clippings.
Impacts
Presence of ungulates negatively affected Mogollon voles through grazing; however, livestock grazing apparently added no additional impact beyond that of elk grazing in these meadows. When there is an objective to provide habitat for Mexican voles, resource managers should reduce impacts by livestock and elk. This may be particularly important when high prey densities for predators are desired. To best detect presence of Mogollon voles, resource managers could use an index of fresh droppings in vole runway rather than live-trapping.
Publications
- Yarborough, R. Fenner. 2004 (expected). Using Mogollon vole runways to measure Mogollon vole abundance in northern Arizona. M.S. Thesis. In preparation: Chambers, C. L., and T. D. Lesh. Effects of ungulate grazing on Mexican voles in wetland meadows of northern Arizona. (To be submitted to The Southwestern Naturalist).
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