2011 Rodent Abundance in WBP Stands and Rodent Predation and Dispersal of Seed

Project: Rodent abundance in whitebark pine stands and rodent predation and dispersal of whitebark pine seed

Agency/Forest or Park/District: Two locations: one location in south-central Montana (Gallatin National Forest) and one location in south-central Washington (Okanogan-Wenatchee National Forest).

Project coordinator:  Teresa Lorenz

Contact:  Teresa Lorenz, 22620 US Hwy 12, Naches, WA 98937, 509-731-5226, lore5748@vandals.uidaho.edu


Dr. Kerri Vierling, Associate Professor, University of Idaho

Source of funding /amount

FHP: $ 5,400

Supplemental funding: $80,000 from University of Idaho

Dates of restoration efforts

July 2011-August 2012


The objectives of this study are (1) to measure relative abundance of rodents in whitebark pine stands, and (2) determine the proportions of whitebark pine seeds predated versus dispersed by rodents in natural settings.

Acres/ha treated  N/A      


To measure abundance of small mammals, at each of 22 plots in Montana and Washington, we placed one 40 x 40 m small mammal trap grid.  Each grid consisted of 25 traps set 10 m apart.  We conducted small mammal trapping at each grid once during autumn (August, September or October) in 2011 and 2012.  Traps were set for 5 day intervals and baited with sunflower seed (treated to prevent germination).  Traps were set on day 1, and checked on days 2, 3, 4, and 5.  All small mammals except shrews were identified to species, ear-tagged, and immediately released.

To determine factors associated with small mammal abundance, we also conducted vegetation surveys at five plots within each small mammal trapping grid for a total of 80 vegetation plots surveyed.  Using point-center quarter methods, we measured shrub and ground cover, canopy cover, density of saplings and trees, and mortality and infection rates for whitebark pine trees.  We also conducted cone counts on 10 mature, canopy-level whitebark pine trees at each study site.

To examine the extent to which rodents pilfer seeds from nutcracker caches, we attempted to mimic Clark’s nutcracker caching behavior by caching 186 whitebark pine seeds at random sites within four of our study sites.  We restricted this portion of our study to Washington plots for logistical reasons.  Caches contained 3 seeds each (average size of nutcracker seed cache) and were buried within 3 cm of the soil surface (average depth of nutcracker seed caches).  We buried a penny within 2 cm of the cache site to enable us to relocate caches using a portable metal detector. We wore gloves when handling seeds and pennies to minimize human odors that may cue rodents to caches.  We returned to these cache sites 10 to 12 months after placement, located the penny with a metal detector and then systematically sifted through the soil to locate seeds and seed hulls.  For each site we noted the number of seeds remaining and number of seed hulls (indicates seeds were consumed by rodents at the cache site).

Planting? If so, source of seedlings? Resistance? No


We successfully completed this project at eight sites in Washington and Montana in 2011, and went on to continue monitoring mammals and seeds in 2012 at two additional sites.   Over the course of two years, we captured 246 individuals representing nine species of small mammal.  In Montana montane voles were by far the most common species captured, whereas in Washington where sites were considerably drier, yellow pine chipmunk and deer mice were the most common species.

We found that 40 percent of seed caches placed to mimic Clark’s nutcracker caches were pilfered by rodents over a one-year period.  Among seed caches pilfered by rodents, we found evidence of seed hulls at only 9 percent of caches. Thus, it is likely that the majority of seed caches pilfered by rodents were not consumed on-site but rather were transported off-site for caching.

Monitoring since completion of the project

            Dates: Summer and Fall 2012

            Plans for future monitoring? None planned at this time

Will outcome meet goals?

Aside from changing the location of one portion of our project from Idaho to Montana, our outcomes met with the objectives of our original proposal.

Future actions/follow up?

None planned at this time