Wildlife Conservation in the Willamette Valley’s Remnant Prairies and Oak Habitats: A Research Synthesis David G. Vesely and Daniel K. Rosenberg Oregon Wildlife Institute Corvallis, Oregon Submitted to: Interagency Special Status Sensitive Species Program U.S. Forest Service / Bureau of Land Management Portland, Oregon Final Report January 2010 Cover photo credits: lone oak, ©Craig DeMars; Fender’s blue butterfly, ©Melissa York; chipping sparrow, ©Nick Saunders Table of Contents EXECUTIVE SUMMARY ......................................................................................4 ACKNOWLEDGEMENTS ....................................................................................5 CHAPTER 1 INTRODUCTION .........................................................................6 Habitat Loss............................................................................................................................................... 7 Future Threats............................................................................................................................................ 8 Wildlife Species Associated with Prairie, Savanna, and Oak Woodlands in the Willamette Valley......... 9 Spatial Scale – Landscape Considerations................................................................................................. 9 Conservation Actions............................................................................................................................... 10 The Synthesis........................................................................................................................................... 10 CHAPTER 2 VEGETATION TRENDS AND DISTRIBUTION IN THE WILLAMETTE VALLEY .....................................................................................11 Grassland Composition and Structure ..................................................................................................... 11 Oak Woodland Plant Communities ......................................................................................................... 12 CHAPTER 3 WILDLIFE COMMUNITIES .........................................................14 Mammals ................................................................................................................................................. 14 Birds ........................................................................................................................................................ 17 Amphibians and Reptiles......................................................................................................................... 18 Invertebrates ............................................................................................................................................ 18 CHAPTER 4 RESEARCH CONDUCTED ON OAK AND PRAIRIE ASSOCIATED WILDLIFE ..................................................................................20 Biodiversity Studies................................................................................................................................. 20 Avian Studies........................................................................................................................................... 22 Mammalian Studies ................................................................................................................................. 36 Reptile and Amphibian Studies ............................................................................................................... 38 Invertebrates ............................................................................................................................................ 41 Research Outside Willamette Valley....................................................................................................... 50 Response to Restoration .......................................................................................................................... 54 CHAPTER 5 FUTURE DIRECTIONS ................................................................60 Research Method ..................................................................................................................................... 61 Selection of Indicator Variables .............................................................................................................. 62 Future Research Directions to Help Guide Habitat Restoration .............................................................. 62 2 CHAPTER 6 SPECIES ACCOUNTS................................................................66 Northern Pacific Rattlesnake (Crotalus viridis oreganus)........................................................................67 Western Pond Turtle (Actinemys marmorata) ......................................................................................... 71 Western Painted Turtle (Chrysemys picta bellii)..................................................................................... 75 Western Gray Squirrel (Sciurus griseus) ................................................................................................. 78 Acorn Woodpecker (Melanerpes formicivorus) ...................................................................................... 82 Streaked Horned Lark (Eremophila alpestris strigata) ........................................................................... 85 Slender-Billed Nuthatch (Sitta carolinenses aculeata)............................................................................ 87 Western Bluebird (Sialia mexicana)........................................................................................................ 90 Chipping Sparrow (Spizella passerina) ................................................................................................... 93 Oregon Vesper Sparrow (Pooecetes gramineus affinins) ........................................................................ 95 Western Meadowlark (Sturnella neglecta) .............................................................................................. 98 Fender’s Blue Butterfly (Icaricia icarioides fenderi) ............................................................................ 100 LITERATURE CITED .......................................................................................102 APPENDIX: WILDLIFE ASSOCIATED WITH GRASSLAND AND WOODLAND HABITAT TYPES IN THE WILLAMETTE VALLEY .........................................122 3 Executive Summary Oregon white oak (Quercus garryanna) and prairie plant communities of Oregon’s Willamette Valley are one of the most imperiled vegetation communities in North America, yet few studies have been conducted on wildlife in these plant communities. The primary goal of our synthesis is to help guide future conservation and restoration efforts of these important wildlife habitats in the Willamette Valley. We synthesize relevant research, and discuss future research and monitoring challenges and needs. We identify several species that are strongly associated with these habitat types in the Willamette Valley, and highlight their ecology and conservation. Our synthesis is intended for managers and researchers working to improve oak and prairie habitats for wildlife in the Willamette Valley. The project was sponsored by the Interagency Special Status Sensitive Species Program (ISSSSP) of the Pacific Northwest Regional Office of the U.S. Forest Service and Oregon/Washington State Office of the Bureau of Land Management. Oak and prairie habitats are managed as wildlife habitat by the Eugene and Salem Districts of the Bureau of Land Management in Oregon and this synthesis is intended to help guide their efforts as well as other efforts to restore oak and prairie vegetation communities for wildlife habitat in the Willamette Valley. Despite the large loss of oak and prairie plant communities in the Willamette Valley, there have been surprisingly little research conducted on the ecology of wildlife in these habitats. What was most striking to us in our review was the large number of in-depth studies of butterfly response to restoration and the paucity of studies of vertebrates that went beyond distributional surveys. Almost all of the vertebrate studies remained descriptive, without understanding potential consequences under different management scenarios. Several studies on Fender’s blue butterfly seemed particularly valuable as a model for linking field studies with management. Developing management-oriented models can provide useful heuristic tools for identifying research needs. The lack of experimentation and formal sampling designs in most of the studies on vertebrates that we reviewed highlights the differences with studies conducted on butterflies and restoration in the Willamette Valley. The majority of studies on vertebrates have used informal sampling approaches to investigate habitat associations at relatively small spatial scales. Understanding habitat relationships to guide restoration is difficult and traditional approaches may not be as useful as other approaches that may involve case studies, adaptive management, and indicator variables that respond to smaller-scale changes from restoration. Research on how vertebrate wildlife responds to restoration in the Willamette Valley is challenging for four primary reasons: (1) disconnect of spatial scale of restoration and animal use patterns, (2) the high variability of each restoration unit and the typical lack of control (non-treated) areas, (3) the extremely high variability