Landscape Features Affecting Squirrel Cache Density and Location Name: Larkin Broussard Title: Landscape Features Affecting Squirrel Cache Density and Location File Format: pptx File Size: KB Key Words: Tree Wells, Squirrel Caching Larkin Broussard EBIO 4100 Winter Ecology, Spring 2018 Mountain Research Station University of Colorado, Boulder

Food Caching Winter means increased food competition (Merritt et al. 2001) Caching takes advantage of food surplus (Delgado et al. 2014) Balance the benefits of caching with risk of losing cache (Delgado et al. 2014) Energy cost (Delgado et al. 2014) Optimal distance between caches (Moore et al. 2007) Food caching is one method used by squirrels and other animals to take advantage of food surpluses, preparing them for times when food will be scarce (winter for instance)(Merritt et al. 2001). Although this “scatter hoarding” behavior is innate, it is important to understand how these animals decide to spend their energy when caching food (Delgado et al. 2014). There is a balance that must be met between the benefits of caching and the risk of losing the cache (Delgado et al. 2014). Why is it important? In the lodgepole forests around Niwot Ridge, Colorado, it is not uncommon to find squirrel caches around tree wells during the winter. Landscape features including canopy cover, tree well characteristics and tree size may effect the energy requirements for caching (Delgado et al. 2014, Moore et al. 2007). Citations: Delgado et al. 2014 Moore et al. 2007 Merritt et al. 2001

What landscape features control the densities of squirrel caches? Possibilities: Tree Density (Canopy Mirror) Tree well characteristics (depth and radius) Tree Size (DBH) Question: What are the landscape features, in lodgepole pine dominated forests, that control the densities of squirrel caches? What features do I want to measure? Tree density Tree well depth Tree well radius Tree width

Methods Two 50 meter transects; one at Sourdough trail, the other at MRS. Both lodgepole pine dominated areas. At four random point along transect, went a random distance perpendicular to the transect tape 50 meters

Point Quarter Method DBH Depth Radius Distance (meters) Measurements: DBH Radius of Tree Well Depth of Tree Well Tree Transect random distance

Canopy Cover Canopy mirror was used to determine percent open canopy Four random canopy cover measurements at each transect (Sourdough and MRS) Measurements averaged Sourdough 4 canopy cover measurements were taken at random places at both transects Open canopy areas measured Canopy mirror was used to determine density (number squares * 1.04) MRS

Results How many caches were found at each site? Chi2 Test P-value=0.23; insignificant 3 16 13 Hypothesis: Landscape features like canopy density will impact the presence of squirrel caches. chi^2 test p-value=0.2253, no significant difference between the trails and presence of caches Canopy density was higher at the MRS transect Canopy Cover: 58.76% open Canopy Cover: 31.98% open

Mountain Research Station T-test P=0.53 Comparison of tree DBH and presence of caches P-value=0.53, not significant Statistical significance vs biologically significant Unequal variance t-test: https://www.graphpad.com/quickcalcs/ttest1.cfm?Format=SD

T-test P=0.087 Comparison of tree well radius and presence of caches P-value=0.087, not significant

T-test P=0.0021*** Comparison of tree well depth and presence of caches P-value=0.0021***, significant

Discussion/ Conclusion No significant difference between Sourdough and MRS Foot traffic Canopy cover Less energy in higher density of trees Tree well characteristics are important Depth Is there an optimal depth? Radius Not as important for cache structure Discussion: No significant difference in density of squirrel caches at MRS and Sourdough trail Depth of tree well significantly correlated with presence of cache More canopy cover at MRS (only transect where caches found) Much more foot traffic around Sourdough trail could influence caching activity If animals think cache may be compromised they may avoid that area (Delgado et al. 2014 discuss the balance between caching risks and loss of caches) MRS has much less foot traffic and higher density of trees Depth may not be deep because of the energy needed to make cache Every animal is different in their preferences, need further research Further research: Instead of looking at the landscape, focus on finding trees with caches and take measurements of only those trees. Why is a smaller tree well depth advantageous for caching animals? Optimal depth? Importance: Species composition of ecosystem Indicator of changes in the future

References Delgado, M.M., Nicholas M., Petrie D.J., Jacobs, L.F. (2014) Fox Squirrels Match Food Assessment and Cache Effort to Value and Scarcity. Plos One. 9(3), 1-8. Merritt, J.F., Lima, M., Bozinovic, F. (2001) Seasonal Regulation in Fluctuating Small Mammal Populations: Feedback Structure and Climate. Oikos. 94(3), 505-514. Moore, J.E., McEuen, A.B., Swihart, R.K., Contreras, T.A., Steele, M.A. (2007) Determinants of Seed Removal Distance by Scatter-Hoarding Rodents in Deciduous Forests. Ecology, 88(10), 2529-2540.