Rachel Jones Winter Ecology Spring 2013 Mountain Research Station, University of Colorado, Boulder Photo by Yellow Wood Guiding

Pine squirrels (Tamiasciurus hudsonicus) are a main prey species Middens can also be a food source for bears (Mattson and Reinhart 1997) Can affect the regeneration rates in some pines (McKinney and Fiedler 2010) Fox squirrels known to choose habitat based on crown and understory composition. (Lee et al. 2009)

How does forest structure affect the amount of time pine squirrels (Tamiasciurus hudsonicus) spend on the forest floor? Will squirrels change their movement based on the openness of a habitat? Does forest structure affect behavior for winter feeding activity? Will squirrels show preferences in caching locations? Photo by E. Golden

H1- Tree density will affect the amount of time the squirrel is spending on the snow. Less trees will force squirrels to move across the ground rather than through the canopy Denser forest will provide more safety, increasing the amount of ground movement. H2- Tree density will change the locations squirrels choose to cache winter stores. Denser stands of trees will provide better tree wells and safety for caching.

Two research areas- Subalpine forest, comprised mostly of spruce and Fir, and Lodgepole Pine forest 6 Randomly selected 10 x 10 meter plots within each area Number of trees within plot recorded Number of full track sets recorded Snowpack and movement type noted Within plots, individual trails were measured Trails were measured from end point to end point in meters Midden/Cache locations found in Lodgepole forest Number of midden/caches and trees recorded

Photo by R. Jones

Tracking depended on snow conditions Snow conditions were consistent Midden/cache sites were difficult to find at subalpine Possibly from recent snow or squirrel population All midden/cache data from lodgepole area Midden/caches were not randomly selected Tracks were sometimes obscured by other trails or by researchers Photo by A. Larson

Forest TypeAverage Trees Average Tracks P-values Subalpine Lodgepole

Average TreesAverage TracksP-values

Forest TypeAverage Length of Trail (m) Average Tree Density P-values Subalpine (LR-.52) Lodgepole (LR-.348)

End Point Codes T- Tree S- Subnivean C- Cache O- Ongoing

P-Value

Both overall data and lodgepole pine data show a significant trend Squirrels have more surface movement with more trees Possibly avoiding areas that have fewer trees Visual observation- tracks generally skirt open areas Supports the H1, showing that denser forests provide more cover for more movement Instead of fewer trees meaning less canopy movement

Average amount of movement within the plot was higher with fewer trees Most frequent end points were trees, meaning movement is from tree base to tree base Many trails were the same squirrel, moving short distances from end point to end point 6.8m 4.9m 2.3m

The correlation between denser clumps of trees and a higher midden/cache number is significant. It is possible that squirrels prefer denser clumps because: Less energy expenditure between midden/cache sites Greater protection within tree clumps Wider tree wells allow for more caching spots Supports H2 that forest density affects caching behavior.

Pine squirrel winter time behavior is affected the forest composition. Prefer denser forests for surface movement Prefer clumps of trees to single trees for caching sites Photo by R. Jones

Thanks to Tim Kittel for project advice Thanks to Michael Klich for research assistance and pack muling

Lee, James C., and David A. Osborn. "Habitat Use By A Dense Population Of Southern Fox Squirrels." Southeastern Naturalist 8.1 (2009): Academic Search Premier. Web. 16 Feb Mattson, D. J., and D. P. Reinhart. "Excavation Of Red Squirrel Middens By Grizzly Bears In The Whitebark Pine Zone." Journal Of Applied Ecology 34.4 (1997): Academic Search Premier. Web. 22 Feb McKinney, Shawn T., and Carl E. Fiedler. "Tree Squirrel Habitat Selection And Predispersal Seed Predation In A Declining Subalpine Conifer." Oecologia (2010): Academic Search Premier. Web. 16 Feb Photos