Source: UNIVERSITY OF WASHINGTON submitted to
63-5926 EASTERN GRAY SQUIRREL ECOLOGY & INTERACTIONS WITH WESTERN GRAY SQUIRRELS ON FT LEWIS, WA.
Sponsoring Institution
Other Cooperating Institutions
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0214929
Grant No.
(N/A)
Project No.
WNZ-1333
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Jul 1, 2009
Project End Date
Jun 30, 2011
Grant Year
(N/A)
Project Director
West, S.
Recipient Organization
UNIVERSITY OF WASHINGTON
(N/A)
SEATTLE,WA 98195
Performing Department
Ecosystem Sciences
Non Technical Summary
Populations of state-threatened western gray squirrels have declined in areas invaded by introduced eastern gray squirrels in Washington, but little is known about competitive interactions between these species. The western gray squirrel is an ecologically important member of oak woodlands, a high priority habitat type for conservation by state agencies. In Washington, the western gray squirrel's status as a threatened species incurs restrictions on some management activities such as tree harvest. Consequently, managers struggle to develop conservation strategies for western gray squirrel habitat occupied by eastern gray squirrels. This study began in 2007 in conjunction with WDFW's project to augment western gray squirrel populations on Fort Lewis. It is using an experimental removal of eastern gray squirrels to determine whether this species is a limiting factor for recovery of western gray squirrels. The project expanded to Klickitat County in 2009.
Animal Health Component
25%
Research Effort Categories
Basic
50%
Applied
25%
Developmental
25%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
3060860107025%
3063899107015%
3070860107020%
3073899107010%
3150860107020%
3153899107010%
Goals / Objectives
The western gray squirrel is a threatened species and thus incurs restrictions on some management activities in Washington such as tree harvest. Managers therefore struggle to develop conservation strategies for western gray squirrel habitat occupied by eastern gray squirrels. Study data collected at the Fort Lewis research site suggest exclusive use of space and some differential use of habitat between the species. The project is now expanding to Klickitat County to determine whether these patterns are found elsewhere and increase the scope of inference. A successful project will effectively test hypotheses that reveal the nature of competition between the species and provide useful recommendations for western gray squirrel recovery.
Project Methods
The eastern and western gray squirrels have been equipped with radio-collars to investigate resource use and interactions between species. This study will use an experimental removal of eastern gray squirrels to determine whether this species is a limiting factor for recovery of western gray squirrels.

Progress 07/01/09 to 06/30/11

Outputs
OUTPUTS: This project provided supplemental funding to support contributions of volunteers to the primary project: eastern gray squirrel ecology and interactions with western gray squirrels in the South Puget Sound Region. The final report for the primary project (WNZ-1287) is given below: Fieldwork on this project has concluded. Analyses and writing of a doctoral dissertation is underway. The dissertation defense is scheduled for January 2013. Resource managers at the Ft. Lewis military reservation in south Puget Sound were regularly apprised of study progress. Reports of work "in progress" for this project were given at several scientific meetings as detailed below. Results of this study were also given at seminars and public presentations at the University of Washington. PARTICIPANTS: Collaborators at the University of Washington included: Dr. John Marzluff: UW faculty colleague and graduate committee member. Dr. Joshua Lawler: UW faculty colleague and graduate committee member. Dr. Christian Grue: UW faculty colleague and Director of the Washington Cooperative Fish and Wildlife Research Unit. Aaron Johnston, Ph.C.: graduate student supported by the project. Collaborating individuals outside the University of Washington included: Dr. Mathew Vander Haegen, Washington Department of Fish & Wildlife: graduate committee member. Collaborating organizations included: Washington Department of Fish & Wildlife. Washington Cooperative Fish and Wildlife Research Unit. School of Environmental and Forest Sciences, University of Washington. Pacific Northwest Cooperative Ecosystem Studies Unit. The Wildlife Society, Washington Chapter. TARGET AUDIENCES: Because this study dealt with a threatened (western gray squirrel) and a highly invasive species (eastern gray squirrel), forest landowners, forest resource managers, agency biologists, and wildlife managers will be interested in the results of the study. Also, the general public will benefit from the information this study provided in helping maintain our native biodiversity. PROJECT MODIFICATIONS: We added an investigation of the competitive relationship between the eastern gray squirrel and the native Douglas's squirrel. Incidental observations indicated that the eastern gray squirrels might have been excluding Douglas's squirrels from useable habitat, so we radio-tagged several Douglas's squirrels to document their movements into eastern gray squirrel territories after we removed the eastern gray squirrels as part of the primary investigation into competitive relations between the western and eastern gray squirrels.

Impacts
The western gray squirrel (Sciurus griseus) is a threatened species in Washington State. The reasons for its decline are not understood fully, although habitat modification, illegal hunting, and competition with introduced eastern gray squirrels (Sciurus carolinensis) in suburban areas are implicated factors. We experimentally removed eastern gray squirrels from selected sites on the Ft. Lewis-McChord military base to evaluate competitive effects on western gray squirrels based on subsequent behavioral interactions, resource use, spatial partitioning, and differences in reproduction, survival, and mass. Fieldwork over the past year has increased the sample size of radio-collared squirrels and the power of statistical contrasts. Work describing fungi in the diets of western and eastern gray squirrels continued. Preliminary analyses indicated low spatial overlap of the two squirrel species with eastern gray squirrels using riparian areas almost exclusively and western gray squirrels predominantly using uplands. Upon completion of the doctoral dissertation, chapters will be submitted for publication in appropriate journals.

Publications

  • Johnston, A.N., S.D. West, and W.M. Vander Haegen. 2012. Competition between eastern and western gray squirrels in the Puget Lowlands, WA. Program abstracts, The International Colloquium for Arboreal Squirrels. February 2012, Kyoto, Japan.
  • Johnston, A.N., S.D. West, and W.M. Vander Haegen. 2012. Competition between eastern and western gray squirrels in the Puget Lowlands, WA. Program abstracts, annual meeting of the American Society of Mammalogists, June 2012, Reno, NV.
  • Johnston, A.N. 2011. Competition between eastern and western gray squirrels in the Puget Lowlands. Program abstracts, annual meeting of the American Society of Mammalogists, 24-28 June, Portland, OR.
  • Johnston, A.N. 2011. Competition between eastern and western gray squirrels in the Puget Lowlands. Program abstracts, annual meeting of the Washington Chapter of The Wildlife Society and the Society for Northwestern Vertebrate Biology, 23-25 March, Gig Harbor, Washington.
  • Johnston, A.N. 2010. Eastern gray squirrel interactions with western gray squirrels. Program abstracts, annual meeting of the Washington Chapter of The Wildlife Society, 16-19 February, Marysville, Washington.


Progress 10/01/07 to 10/01/08

Outputs
OUTPUTS: This project augments the travel, equipment, and supplies budgets of the project, "Eastern gray squirrel ecology and interactions with western gray squirrels in the South Puget Sound region (WNZ-1287)." The western gray squirrel is a threatened species in Washington State. Introduced eastern gray squirrels have displaced native tree squirrels elsewhere and may be a serious threat to western gray squirrels in the Puget Trough. The objective of this study is to describe the ecology of the eastern gray squirrel and its interactions with western gray squirrels on Fort Lewis, WA. We will employ an experimental design to describe the ecology of eastern and western gray squirrels by comparing population parameters, habitat use, and other ecological metrics between areas where eastern and western gray squirrels coexist and areas where eastern gray squirrels have been removed. A graduate student was selected to conduct the fieldwork and the first cohort of eastern gray squirrels was radio-collared and records of their use of habitat initiated. PARTICIPANTS: Aaron Johnston, University of Washington graduate student; Stephen West, Professor, University of Washington, Mathew Vander Haegen, Washington Department of Fish & Wildlife TARGET AUDIENCES: Washington Department of Fish & Wildlife biologists and managers, land managers at Ft. Lewis, Washington PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
This project will help assess the potential negative effects of introduced eastern gray squirrels on western gray squirrels. Results will be incorporated in management plans for the enhancement of western gray squirrel populations where eastern gray squirrels co-occur.

Publications

  • No publications reported this period