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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
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
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
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?
Study Site
http://www.vermont-map.org/detailed.htm
Battell Research Forest
• Two different types of trap were affixed to 60 haphazardly selected trees
A trapping station – the smaller Sherman trap rests atop a platform facing the tree trunk with the larger Tomahawk resting below.
• 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
Methods: Live-Trapping
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…
• 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
Glaucomys capture success
• 20 individuals marked
• 10 different individuals recaptured on 18 total occasions
• Lincoln-Peterson method: population size estimate
MaximumDensity
(animals/ha)
Minimum Density
(animals/ha)
Total Flying Squirrels 3.8 ± 1.0 2.3 ± 0.6
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
Results: Mark-recapture
• Clusters of traps had higher capture rates
-Northern Cluster8.3% capture success
-Central Cluster13.1% capture success
-Southern Cluster6.2% capture success
• Is a cluster of high capture rate due simply to one individual?
Differential trap success
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?
Locomotion
http://aparadigmshift.files.wordpress.com/2009/02/nfsquir.jpg
• Flying squirrels do not fly, they glide…
…but what does that even mean?
Locomotion
Locomotion
Locomotion
Locomotion
Roosting ecology• Flying squirrels employ
existing tree cavities and external nests as diurnal refuges
• Winter is an energetically costly period for maintaining body heat
• Flying squirrels engage in group nesting behavior of 4-7 individuals to reduce heat loss
http://www.jennifermarohasy.com/blog/archives/Ann%20Novek_Siberian%20Squirrel_lendorav5.jpg
http://www.ealt.ca/media/imagic/Betty_Fisher_flying_squirrel_babies_in_nest_hole.jpg
• 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
Methods: Radio-telemetry
• Roost trees were larger at the base than random trees (p = 0.001)
Results: Roost trees
• The overstory composition was not different at roost sites and random sites (all p > 0.519)
• Roosting trees not always in close proximity with foraging regions
• Foraging regions seemingly associated with winter tree cover
Roost sites in relation to trap success
Evidence of shared roosts
• Maple snag
- 4 male individuals
- visible midden at base
• Pine snag
- 2 male individuals
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?
• Group roosting squirrels exhibit pronounced home range overlap
• Shared winter foraging grounds?
• Only one recaptured northern flying squirrel
Species movement patterns
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
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?
AcknowledgementsSteve TrombulakJoanna Shipley
Mark Spritzer, Helen YoungEco/Evo Bio lunch group
Bill HegmanPeter and Cathy Tuttle
Vicki Major, Sarah FroebelCharlie Hofmann, Chris Free, Zöe Sheldon, Tripp Burwell, Catherine Timmins,
Steve Heck, Kei Katsura, Greg Larsen, Andrew Locke, Mithra HarivandiMatt Westman, Ian Evans, Jordan Valen
FundingLake Champlain Research Consortium
Senior Research Fellowship
Questions?
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