Flying squirrels were live-trapped in a Vermont old-growth forest to study their population density and winter roosting behavior. The population was estimated to be between 2.3-3.8 animals per hectare, dominated by southern flying squirrels. Radio-tracking showed that roost trees were larger and often involved group nesting in cavities or snags. Foraging areas overlapped between individuals, though roost sites were not always near foraging regions. Further research is needed to better understand dispersal patterns and genetic relatedness between group-nesting squirrels.

1. Use of winter roost trees by southern flying
squirrels (Glaucomys volans) in a Vermont
old-growth forest
Emerson Tuttle (‘09)
May 6, 2009
Middlebury College Biology Department

2. Flying squirrels: Genus Glaucomys
• Unique nocturnal rodents
• Two species
- Northern (G. sabrinus)
- Weight: 75-140g
- Southern (G. volans)
- Weight: 46-85g
• Consumers of hypogeous
mycorrhizal fungi and hard
mast, respectively
• Competition?
- Little evidence of local sympatry
Top: Ralph Palmer, www.flickr.com; Bottom: Phil Myers, www.discoverlife.org

3. Flying squirrels: Genus Glaucomys
• Northern Appalachian
region one of the only
areas where the species
overlap in range
• Associated with old-
growth forest structure
• Influence on forest
composition as dispersers
• Listed by the Vermont Fish
& Wildlife Department as
a species of conservation
concern in the state
Don E. Wilson, http://www.discoverlife.org

4. Study Questions
• What is the density of flying squirrels in a
Vermont old-growth forest?
2) What characterizes late fall/winter roost
sites employed by flying squirrels?
3) What are the habitat preferences of
southern and northern flying squirrels,
and how do their distributions overlap?

5. Study Site
Battell Research Forest
http://www.vermont-map.org/detailed.htm

6. Methods: Live-Trapping
• Two different types of trap were affixed to 60
haphazardly selected trees
• Traps baited one hour
before sunset with a
mixture of peanut butter,
oats, and apples
• 8-12 cotton balls included
for bedding material
• All traps checked the next
morning for captures
A trapping station – the smaller Sherman trap rests
atop a platform facing the tree trunk with the
larger Tomahawk resting below.

7. Methods: Mark-recapture
•Bag ‘em
• Identify sex and
species
• Mark back with a
unique hair dye
design
•Release the animal
That is if it wants to leave…

8. Glaucomys capture success
• Trap-nights: 1489
• Total flying squirrel caught: 67
- Southern: 40
- Northern: 10
- Unidentified: 17
• Trap success: 4.50%
- Sherman success: 6.90%
- 55 captures / 797 trap-nights
- Tomahawk success: 1.73%
-12 captures / 692 trap-nights
A southern flying squirrel peering out of a
Sherman trap

9. Results: Mark-recapture
• 20 individuals marked
• 10 different individuals Maximum Minimum
recaptured on 18 total Density Density
occasions (animals/ha) (animals/ha)
• Lincoln-Peterson method: Total Flying
population size estimate 3.8 ± 1.0 2.3 ± 0.6
Squirrels
Northern F.s. 0.5 ± 0.2 0.3 ± 0.1
Southern F.s. 2.7 ± 0.7 1.6 ± 0.4
Animal density estimates based on
literature values of minimum (100 m) and
maximum (160 m) effective home range
radii of flying squirrels

10. Differential trap success
• Clusters of traps had
higher capture rates
-Northern Cluster
8.3% capture success
-Central Cluster
13.1% capture success
-Southern Cluster
6.2% capture success
• Is a cluster of high capture
rate due simply to one
individual?

11. Study Questions
• What is the density of flying squirrels in a
Vermont old-growth forest?
2) What characterizes late fall/winter roost
sites employed by flying squirrels?
3) What are the habitat preferences of
southern and northern flying squirrels,
and how do their distributions overlap?

12. Locomotion
• Flying squirrels do not fly, they glide…
…but what does that even mean?
http://aparadigmshift.files.wordpress.com/2009/02/nfsquir.jpg

13. Locomotion

14. Locomotion

15. Locomotion

16. Locomotion

17. Roosting ecology
• Flying squirrels employ
existing tree cavities and
external nests as diurnal
refuges
• Winter is an energetically
costly period for maintaining
body heat
http://www.jennifermarohasy.com/blog/archives/Ann
%20Novek_Siberian%20Squirrel_lendorav5.jpg
• Flying squirrels engage in
group nesting behavior of
4-7 individuals to reduce
heat loss
http://www.ealt.ca/media/imagic/Betty_Fisher_flying_squirrel_babies_in_nest_h
ole.jpg

18. Methods: Radio-telemetry
• Six southern flying
squirrels were fitted
with radio collars
• For proper fitting,
animals were
anesthetized in the
field with isoflurane
• Tracking to diurnal
dens occurred
throughout the late
fall and winter
months

19. Results: Roost trees
•• The overstory composition was not
Roost trees were larger at the base
than randomroost sites=and random
different at trees (p 0.001)
sites (all p > 0.519)

20. Roost sites in relation to trap success
• Roosting trees not
always in close proximity
with foraging regions
• Foraging regions
seemingly associated
with winter tree cover

21. Evidence of shared roosts
• Maple snag
- 4 male individuals
- visible midden at
base
• Pine snag
- 2 male individuals

22. Study Questions
• What is the density of flying squirrels in a
Vermont old-growth forest?
2) What characterizes late fall/winter roost
sites employed by flying squirrels?
3) What are the habitat preferences of
southern and northern flying squirrels,
and how do their distributions overlap?

23. Species movement patterns
• Group roosting squirrels
exhibit pronounced
home range overlap
• Shared winter foraging
grounds?
• Only one recaptured
northern flying squirrel

24. Conclusions
• Population dominated by the smaller, more
aggressive southern flying squirrel
• Roost trees were larger than random trees, but
canopy cover near roosts was similar
– Selection of winter roost sites based on target tree
characteristics
• Group roosting observed in a distinct tree motif
– Snapped snag; cavities at apex of stem
• Foraging sites show marked overlap between
individuals

25. Future directions
• Dispersal patterns in early spring and roost tree use in
warmer seasons?
• Selection criteria for spatial foraging preference?
• Genetic analysis of relatedness between group-nesting
individuals?
• Role of Strongyloides robustus in determining flying
squirrel population dynamics?

26. Acknowledgements
Steve Trombulak
Joanna Shipley
Mark Spritzer, Helen Young
Eco/Evo Bio lunch group
Bill Hegman
Peter and Cathy Tuttle
Vicki Major, Sarah Froebel
Charlie Hofmann, Chris Free, Zöe Sheldon, Tripp Burwell, Catherine Timmins,
Steve Heck, Kei Katsura, Greg Larsen, Andrew Locke, Mithra Harivandi
Matt Westman, Ian Evans, Jordan Valen
Funding
Lake Champlain Research Consortium
Senior Research Fellowship

27. Questions?