Rachel JonesWinter Ecology

Spring 2013Mountain Research Station, University

of Colorado, Boulder

Forest structure and supranivean behavior of

pine squirrels

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)

Introduction

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?

Question

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.

Hypothesis

Two research areas- Subalpine forest, comprised mostly of spruce and Fir, and Lodgepole Pine forest6 Randomly selected 10 x 10 meter plots within

each areaNumber of trees within plot recordedNumber of full track sets recordedSnowpack and movement type noted

Within plots, individual trails were measuredTrails were measured from end point to end point

in meters

Midden/Cache locations found in Lodgepole forestNumber of midden/caches and trees recorded

Methods

Photo by R. Jones

Photo by R. Jones

Tracking depended on snow conditionsSnow conditions were consistent

Midden/cache sites were difficult to find at subalpinePossibly from recent snow or squirrel

populationAll midden/cache data from lodgepole areaMidden/caches were not randomly selected

Study Limitations

Tracks were sometimes obscured by other trails or by researchers

Photo by A. Larson

Results- Number of trees and tracks

10 15 20 25 30 35 40 45 50 550

50

100

150

200

f(x) = 3.32053571428571 x − 16.5223214285714R² = 0.940058030786631f(x) = 1.88627983698816 x + 14.9534251892102R² = 0.607268151017652

Number of Track Sets to Trees

SubalpineLinear (Subalpine)Lodgepole

Number of Trees

Num

ber

of F

ull

Trac

k Se

ts

Forest Type

Average Trees

Average Tracks

P-values

Subalpine 31.83 75 0.068Lodgepole 41.67 121.83 0.0014

Results

10 15 20 25 30 35 40 45 50 550

50

100

150

200

f(x) = 2.7861717851864 x − 3.9751464389336R² = 0.738972713712795

Number of Track Sets to Trees

Number of TreesNum

ber

of F

ull T

rack

Se

ts

Average Trees Average Tracks

P-values

36.75 98.41 .00337

Forest Type

Average Length of Trail (m)

Average Tree Density

P-values

Subalpine 6.837 31.83 .0022 (LR-.52)Lodgepole 3.713 41.67 .0001

(LR- .348)

Results- Length of Movement

10 15 20 25 30 35 40 45 50 550.01.02.03.04.05.06.07.08.09.0

10.0

f(x) = − 0.065982142857143 x + 6.4825892857143R² = 0.22238128719107

f(x) = 0.0491249433986675 x + 5.06716152403131R² = 0.109747525777205

Track Lengths vs. Tree Density

SubalpineLinear (Subalpine)LodgepoleLinear (Lodgepole)

Tree Density

Ave

rage

Tra

ck L

engt

hs

Results- Length of Movement

End Point CodesT- TreeS- SubniveanC- CacheO- Ongoing

T/T

T/S

T/C

T/O

C/C

C/S

S/S

0 2 4 6 8 10 12

Movement End Points

LodgepoleSubalpine

Frequency

End

Poin

ts

Results- Midden/Cache

0 2 4 6 8 10 12 14012345

f(x) = 0.261194029850746 x + 0.425373134328358R² = 0.89188205314889

Number of Caches vs. Trees

Number of TreesNum

ber

of C

ache

s in

V

icin

ity

P-Value 0.0046

Both overall data and lodgepole pine data show a significant trend Squirrels have more surface movement with

more treesPossibly 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 movementInstead of fewer trees meaning less canopy

movement

Discussion- Number of trees and tracks

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 baseMany trails were the same squirrel, moving

short distances from end point to end point

Discussion- Length of Movement

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 sitesGreater protection within tree clumpsWider tree wells allow for more caching spots

Supports H2 that forest density affects caching behavior.

Discussion- Midden/Cache

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

Summary

Photo by R. Jones

Thanks to Tim Kittel for project advice

Thanks to Michael Klich for research assistance and pack muling

Acknowledgements

Lee, James C., and David A. Osborn. "Habitat Use By A Dense Population Of Southern Fox Squirrels." Southeastern Naturalist 8.1 (2009): 157-166. Academic Search Premier. Web. 16 Feb. 2013.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): 926-940. Academic Search Premier. Web. 22 Feb. 2013.McKinney, Shawn T., and Carl E. Fiedler. "Tree Squirrel Habitat Selection And Predispersal Seed Predation In A Declining Subalpine Conifer." Oecologia 162.3 (2010): 697-707. Academic Search Premier. Web. 16 Feb. 2013.Photoshttp://ywguiding.wordpress.com/2010/04/06/spring-is-on-the-way/pine-squirrel/http://allarsonphotography.com/2010/12/

Literature Cited