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?