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Brush mouse (Peromyscus boylii) occurrences in Southern Oregon.

The Brush Mouse (Peromyscus boylii) is common in mountainous regions of California, the southwestern United States, and northern Mexico (Kalcounis-Rueppell and Spoon 2009). Until recently the Brush Mouse had not been documented in Oregon, but was thought to occur near the California border between Cave Junction and Lakeview, Oregon (Verts and Carraway 1998:503). Brush Mice were captured within 3.2 km of the Oregon border in Beswick, California (Grinnell 1933), but were not detected in small mammal studies near Keno, Oregon (Verts and Carraway 1998:503). Burkot and others (1999) captured Brush Mice in Josephine and Jackson Counties in southern Oregon during their study of Lyme disease vectors, but did not acknowledge that the captures represented a range expansion for the species. Their records have been the only documentation of this species in Oregon.

We captured Brush Mice within the Cascade-Siskiyou National Monument, Jackson County, Oregon during our study of small mammal responses to cattle grazing (Johnston 2006; Johnston and Anthony 2008). We sampled 16 sites distributed equally between oak woodlands and mixed-conifer forests on the Monument. At each site, we trapped small mammals for 5 and 6 nights in the fall of 2003 and 2004, respectively, using Sherman traps (HB Sherman Traps, Inc., Tallahassee, FL) baited with peanut butter and rolled oats. Traps were spaced at 15-m intervals and distributed as 10 X 10 grids along streams. We captured 4 Brush Mice at 2 sites in oak woodlands along Skookum Creek, an ephemeral stream within 5 km of the California border (UTM: Zone 10, 547283E, 4655081N and 550150E, 4653485N, NAD83). We submitted tissue samples from 2 individuals to the laboratory of Jan Zinck at Portland State University for genetic analyses. Results indicated that our specimens were P. b. rowleyi (Fig. 1) and physical descriptions were consistent with that identification (Kalcounis-Rueppell and Spoon 2009). The Burke Museum of Natural History and Culture at the University of Washington, Seattle, accessioned all Brush Mice and other small mammals collected during this study (Oregon State University Animal Use and Care Permit No. 2691).

In northern California, Brush Mice occur at >2000 m in elevation in rock outcroppings, brushy areas, or forested areas where boulders, brush piles, and downed wood provide shelters (Wilson and Ruff 1999). Our sites along Skookum Creek were at 1209 m and 1046 m in elevation and were dominated by Oregon White Oak (Quercus garryana) with scattered Ponderosa Pine (Pinus ponderosa) and Western Juniper (Juniperus occidentalis). Buckbrush (Ceanothus cuneatus) was abundant on these sites, and common grasses included Lemmon's Needlegrass (Achnatherum lemmonii), Idaho Fescue (Festuca idahoensis), Medusa-head Rye (Taeniatherum caput-medusae), and Bulbous Bluegrass (Poa bulbosa). Although brush piles and downed wood were scarce at these sites, all 7 capture locations for Brush Mice were within 25 m of the stream, which was dry with many exposed rocks and moderate cover by willows (Salix spp.). Canopy cover at these locations averaged 25% based on ocular estimates, and groundcover was composed mainly of grass and deciduous litter.

Brush Mice represented <1% of the small mammals captured in our study. Deer Mice (P. maniculatus) and Pinyon Mice (P. truei) were the most common small mammals captured at sites with Brush Mice, and accounted for 53 and 27% of the total captures, respectively. These species appeared to use areas similar to Brush Mice because Deer Mice were captured at the same trap stations as Brush Mice, and Pinyon Mice were captured at adjacent stations 15 m away. We also captured Dusky-footed Woodrats (Neotoma fuscipes), House Mice (Mus musculus), Townsend's Voles (Microtus townsendii), a Trowbridge's Shrew (Sorex trowbridgii), a Vagrant Shrew (S. vagrans), a California Kangaroo Rat (Dipodomys californiens), and a Harvest Mouse (Reithrodontomys megalotis) at sites where we captured Brush Mice.

It is unclear whether findings of Brush Mice in Oregon represent a recent range expansion or that the species was difficult to document because populations are sparsely distributed at its northern range limit. Skookum Creek flows from the southeast face of Soda Mountain, which has sharp transitions from arid ecosystems with flora and fauna characteristic of California and the Great Basin to those of the Cascade Range. Such transitions may act as dispersal barriers for Brush Mice to reach oak woodlands common elsewhere in southern Oregon. Trapping records to date suggest their range is limited to the extreme southern portion of Oregon near Medford.

We were surprised that genetic analyses identified our specimens as P. b. rowleyi because range maps suggest P. b. boylii would be the most likely subspecies found in southern Oregon (Kalcounis-Rueppell and Spoon 2009). Each of 4 subspecies of Brush Mice is associated with distinct regions: P. b. boylii (northern California), P. b. glasselli (Gulf of California), P. b. utahensis (Utah), and P. b. rowleyi (southwestern United States). Our captures of P. b. rowleyi suggest a northern range expansion for this subspecies, but further study is needed to test and verify this hypothesis.

Key words: Brush Mouse, geographic distribution, oak woodlands, Oregon, Peromyscus boylii

Acknowledgements.--This study was funded by World Wildlife Fund, Bureau of Land Management, and the Oregon Cooperative Fish and Wildlife Research Unit at Oregon State University. We thank J Zinck for providing genetic analyses at Portland State University and our field assistants V Marr and T Phillips.

LITERATURE CITED

BURKOT TR, CLOVER JR, HAPP CM, DEBESS E, MAUPIN GO. 1999. Isolation of Borrelia burgdorferi from Neotoma fuscipes, Peromyscus maniculatus, Peromyscus boylii, and Ixodes pacificus in Oregon. American Journal of Tropical Medicine and Hygiene 60:453457.

GRINNELL J. 1933. Review of the recent mammal fauna of California. University of California Publications in Zoology 40:71-234.

JOHNSTON AN. 2006. Relative abundance and habitat associations of small mammals in two forest types in southern Oregon [thesis], Corvallis, OR: Oregon State University. 151 p.

JOHNSTON AN, ANTHONY RG. 2008. Small-mammal microhabitat associations and response to grazing in Oregon. Journal of Wildlife Management 72: 1736-1746.

KALCOUNIS-RUEPPELL MC, SPOON TR. 2009. Peromyscus boylii (Rodentia: Cricetidae). Mammalian Species 838:1-14.

VERTS BJ, CARRAWAY LN. 1998. Land mammals of Oregon. Berkeley, CA: University of California Press. 668 p.

WILSON DE, RUFF S, editors. 1999. The Smithsonian book of North American mammals. Smithsonian Institution Press. 750 p.

Department of Fisheries and Wildlife Biology, 104 Nash Hall, Oregon State University, Corvallis, OR 97331 USA; Current address: School of Environmental and Forest Sciences, University of Washington, Box 352100, Seattle, WA 98195 USA (ANJ), aaronj5@u.washington.edu; Department of Fisheries and Wildlife Biology, 104 Nash Hall, Oregon State University, Corvallis, OR 97331 USA (RGA). Submitted 20 July 2013, accepted 9 October 2013. Corresponding Editor: Robert Hoffman.
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Title Annotation:GENERAL NOTES
Author:Johnston, Aaron N.; Anthony, Robert G.
Publication:Northwestern Naturalist: A Journal of Vertebrate Biology
Article Type:Report
Geographic Code:1USA
Date:Mar 22, 2014
Words:1091
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