EASTERN GRAY SQUIRREL ECOLOGY AND INTERACTIONS WITH WESTERN GRAY SQUIRRELS ON JOINT BASE LEWIS-MCCHORD

• Sponsoring Institution: Other Cooperating Institutions
• Project Status: COMPLETE
• Funding Source: STATE
• Reporting Frequency: Annual
• Accession No.: 0227650
• Project Start Date: Jul 1, 2011
• Project End Date: Jun 30, 2012
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UNIVERSITY OF WASHINGTON
4333 BROOKLYN AVE NE
SEATTLE,WA 98195

Performing Department
Wildlife Science

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 (Linders and Stinson 2007). The western gray squirrel is an ecologically important member of oak woodlands, a high priority habitat type for conservation by state agencies. Intensive efforts by the Washington State Department of Fish and Wildlife (WDFW) are underway to recover western gray squirrels on Joint Base Lewis-McChord where one of the three remaining populations in Washington is critically low and interacts with eastern gray squirrels. This study is evaluating threats to recovery of western gray squirrels by eastern gray squirrels, thereby filling important information gaps identified by WDFW's recovery plan for western gray squirrels. Continued management of western gray squirrels without understanding threats posed by eastern gray squirrels risks further population declines of western gray squirrels and jeopardy of recovery efforts. This multi-year project has benefitted greatly from past Aquatic Lands Enhancement Account (ALEA) grants and this current project will complete the final six months of post-treament data collection on experimental removals of eastern gray squirrels.

Animal Health Component

100%

Research Effort Categories

Basic

(N/A)

Applied

100%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
135	0860	1070	100%

Knowledge Area
135 - Aquatic and Terrestrial Wildlife;

Subject Of Investigation
0860 - Endangered species;

Field Of Science
1070 - Ecology;

Keywords

squirrels

washington

hairs

fur

excreta

feeding behavior

ecological competition

threatened species

indigenous species

introduced species

wildlife management

population distribution

population dynamics

wildlife habitats

habitat preferences

habitat conservation

animal ecology

species diversity

data collection

model validation

Goals / Objectives
The objective of this study is to test hypotheses that reveal the nature of competition between eastern and western gray squirrels and provide useful recommendations for western gray squirrel recovery. Expected Benefits: This study will provide an evaluation of threats to recovery and management of western gray squirrels posed by eastern gray squirrels. In addition, our intensive study of habitat associations for both gray squirrel species should not only describe habitat needs for western gray squirrels but also suggest ways managers can exploit differences in habitat requirements to favor this species over eastern gray squirrels. Measurements of survival and reproduction on western gray squirrels at Joint Base Lewis-McChord will complement similar data collected on this species elsewhere in Washington and will be useful to parameterize population models. Results of this study will be available in a dissertation at the University of Washington and submitted for publication in professional journals. Potential manuscript titles include: 1. Western gray squirrel response to removal of eastern gray squirrels in Washington. 2. Habitat selection by eastern and western gray squirrels at multiple scales. 3. Nest-site selection by eastern and western gray squirrels at multiple scales. 4. Diets of eastern and western gray squirrels in Washington.

Project Methods
Specific field objectives for the final six months of study include the following: 1. Collect the post-treatment data on resource partitioning and fitness (e.g. mass, survival, fecundity) for squirrels at control and removal sites needed to evaluate competition between gray squirrel species on Joint Base Lewis-McChord. 2. Collect fecal pellets and squirrel stomachs for a comparative diet study. 3. Monitor hair-snags in Klickitat County to describe distribution of eastern and western gray squirrels in southern Washington. Implementation: This study began in 2007 in conjunction with the Washington State Department of Fish and Wildlife's (WDFW's) project to augment populations of western gray squirrels on Joint Base Lewis-McChord. Together, we have equipped eastern and western gray squirrels with radio-collars to investigate resource use and interactions between species. This study has conducted experimental removals of eastern gray squirrels to determine whether this species is a limiting factor for recovery of western gray squirrels. To complete this experiment, we need volunteers to monitor gray squirrels with radio-telemetry for six months. We also need volunteers to continue monitoring hair-snags in Klickitat County to describe distribution of gray squirrels in southern Washington which will expand our scope of inference.

Progress 07/01/11 to 06/30/12

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.