A Conservation Strategy for Great Gray Owls (Strix nebulosa) in California Joanna X. Wu Helen L. Loffland Rodney B. Siegel Chris Stermer THE INSTITUTE FOR BIRD POPULATIONS The Institute for Bird Populations A Conservation Strategy for Great Gray Owls in California Interim version (October 2016) under review by the California Department of Fish and Wildlife Artwork by: Lauren Helton Photographs (front and back cover) by: Cameron Rognan, Stanislaus National Forest. The Institute for Bird Populations A Conservation Strategy for Great Gray Owls in California A Conservation Strategy for Great Gray Owls (Strix nebulosa) in California Joanna X. Wu The Institute for Bird Populations Helen L. Loffland* The Institute for Bird Populations Rodney B. Siegel The Institute for Bird Populations Chris Stermer California Department of Fish and Wildlife *Corresponding author: [email protected] The Institute for Bird Populations, P.O. Box 1346, Point Reyes Station, CA 94956. Recommended citation: Wu, J. X., H. L. Loffland, R. B. Siegel, C. Stermer. 2016. A Conservation Strategy for Great Gray Owls (Strix nebulosa) in California. Interim version 1.0. The Institute for Bird Populations and California Partners in Flight. Point Reyes Station, California. The Institute for Bird Populations A Conservation Strategy for Great Gray Owls in California Dedication This Strategy is dedicated to the memory of Jon Winter, for his many years of work on and devotion to the study and conservation of Great Gray Owls. Photo: Chevron Corporation. October 2, 1986, Yosemite National Park. The Institute for Bird Populations A Conservation Strategy for Great Gray Owls in California TABLE OF CONTENTS List of Figures ................................................................................................................................ iv List of Tables ................................................................................................................................ vii Executive Summary ........................................................................................................................ 1 Summary of Conservation Actions ................................................................................................. 3 Definitions ................................................................................................................................... 4 Recommended Conservation Actions ......................................................................................... 5 Delineation of Great Gray Owl Core Management Areas (CMAs) ........................................ 5 Managing Meadows and Other Foraging Habitat ................................................................... 6 Managing Forest Habitats ........................................................................................................ 7 Surveys Protocols and Incidental Sightings ............................................................................ 9 Reducing Vehicle Strikes ...................................................................................................... 10 Residential and Agricultural Development and Land Acquisition ........................................ 10 Monitoring and Research Needs ............................................................................................ 11 Acknowledgments......................................................................................................................... 14 Introduction to this Strategy.......................................................................................................... 15 Information Sources ...................................................................................................................... 16 Species Description and Ecology .................................................................................................. 18 Physical Description and Taxonomy......................................................................................... 18 Distribution and Population Status ............................................................................................ 19 Habitat Requirements ................................................................................................................ 22 Breeding Season .................................................................................................................... 22 Winter .................................................................................................................................... 23 Habitat Photo Gallery ................................................................................................................ 25 Examples of Great Gray Owl Habitat Near Known Nest Sites ............................................. 25 Diversity of Nest Trees Used................................................................................................. 27 Food Habits ............................................................................................................................... 27 Life History and Population Ecology ........................................................................................ 29 Reproduction and Phenology .................................................................................................... 29 Mortality Factors ....................................................................................................................... 30 Home Range .............................................................................................................................. 31 Migration ................................................................................................................................... 32 Species Conservation, Habitat Management, and Recommendations for Land Managers .......... 33 History of Great Gray Owl Protection in California ................................................................. 33 ii The Institute for Bird Populations A Conservation Strategy for Great Gray Owls in California Current Management Status ...................................................................................................... 33 Management on National Park Service Lands ...................................................................... 33 Management on USDA Forest Service Lands ....................................................................... 34 Management on Privately-Owned Lands .............................................................................. 35 Great Gray Owls Outside the Greater Yosemite Area .............................................................. 36 El Dorado, Amador, and Calaveras Counties ........................................................................ 37 Sierra, Yuba, and Plumas Counties ....................................................................................... 37 Modoc County ....................................................................................................................... 38 Delineating Great Gray Owl Core Management Areas ............................................................ 41 Examples of Core Management Area Configurations ........................................................... 44 Potential Threats and Recommendations to Minimize Them ....................................................... 48 Livestock Grazing ..................................................................................................................... 48 Outreach and Land Acquisition ............................................................................................. 52 Timber Harvest .......................................................................................................................... 53 Artificial Nests ....................................................................................................................... 58 Human Activity ......................................................................................................................... 59 Vehicle Strikes ....................................................................................................................... 59 Land Development ................................................................................................................ 61 Rodent-Control ...................................................................................................................... 63 Off-Highway Vehicles ........................................................................................................... 64 Birdwatchers and Photographers ........................................................................................... 65 Forest Wildfire .......................................................................................................................... 66 Climate Change ......................................................................................................................... 68 Drought and Conifer Mortality .............................................................................................. 70 Disease ...................................................................................................................................... 70 Predation.................................................................................................................................... 71 Risks of a Small Population Size .............................................................................................. 72