forest structure and supranivean behavior of pine squirrels
DESCRIPTION
Forest structure and supranivean behavior of pine squirrels. Rachel Jones Winter Ecology Spring 2013 Mountain Research Station, University of Colorado, Boulder. Photo by Yellow Wood Guiding. Introduction. Pine squirrels ( Tamiasciurus hudsonicus) are a main prey species - PowerPoint PPT PresentationTRANSCRIPT
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