AN ABSTRACT OF THE THESIS OF Allison Patterson for the degree of Master of Science in Wildlife Science presented on November 13, 2012 Title: Breeding and Foraging Ecology of Caspian Terns Nesting on Artificial Islands in the Upper Klamath Basin, California Abstract approved: Daniel D. Roby Availability of suitable nesting habitat that is free of nest predators and provides access to adequate prey resources within commuting distance is a major factor limiting seabird populations. Caspian terns (Hydroprogne caspia ) in western North America have shifted their breeding habitat from naturally occurring habitats in interior wetlands, lakes, and rivers to primarily human-created habitats in coastal bays and estuaries. This shift has brought Caspian terns into conflict with fisheries of conservation concern, in particular anadromous salmonids. Prior to the 2010 breeding season, three artificial islands were built in the Klamath Basin National Wildlife Refuge (NWR) Complex as alternative nesting habitat for Caspian terns currently nesting at the world’s largest colony for the species, near the mouth of the Columbia River, Oregon. I investigated the efficacy of habitat creation (island building) and social attraction (decoys and recorded vocalizations) for establishing new breeding colonies in the Upper Klamath Basin, California. In 2010, approximately 258 pairs of Caspian terns attempted to nest on the new islands and raised an average of 0.65 fledglings/breeding pair; in 2011, 222 pairs attempted to nest and raised an average of 0.11 fledglings/breeding pair. Competition with California and ring-billed gulls ( Larus californicus and L. delawarensis ) for nesting space, gull predation on Caspian tern eggs and chicks, low water levels, and depredation by great horned owls (Bubo virginianus ) were the primary factors limiting colony development and productivity, especially in 2011. The immediate response by Caspian terns to habitat creation and social attraction in the Upper Klamath Basin demonstrates that these can be effective restoration techniques to establish new breeding colonies where nesting habitat is a major limiting factor; however, continued management of other limiting factors (e.g., control of on-colony predators and competitors) will likely be necessary to promote the development of established, self-sustaining breeding colonies on these artificial islands. Efforts to conserve and restore seabird colonies can be compromised by low prey availability within foraging distance of the breeding colony. I used GPS telemetry to study the fine-scale foraging behavior of Caspian terns nesting at two newly established colonies and cluster analysis to discriminate behavioral states based on movement characteristics. Terns breeding at the Sheepy Lake colony spent less time at the colony (52% of the day) than terns breeding at the Tule Lake colony (74%). Caspian terns breeding at Sheepy Lake foraged more extensively than terns breeding at Tule Lake; the foraging trips of Sheepy Lake terns lasted longer (median = 186 min) and were longer-distance (27 km) compared to those of Tule Lake terns (55 min and 6 km, respectively). Between-colony differences in foraging behavior corresponded to 5% lower average body mass of breeding adults and significantly lower size-adjusted body mass of chicks at the Sheepy Lake colony compared to the Tule Lake colony. Proximity to high-quality foraging areas influenced the foraging behavior and parental care of breeding Caspian terns, which in turn had effects on nesting success. The successful use of GPS telemetry to study the fine-scale foraging behavior of Caspian terns represents a significant advance in our ability to investigate the foraging ecology of this species and other moderate-sized seabirds. © Copyright by Allison Patterson November 13, 2012 All Rights Reserved Breeding and Foraging Ecology of Caspian Terns Nesting on Artificial Islands in the Upper Klamath Basin, California by Allison Patterson A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented November 13, 2012 Commencement June 2013 Master of Science thesis of Allison Patterson presented on November 13, 2012. APPROVED: Major Professor, representing Wildlife Science Head of the Department of Fisheries and Wildlife Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Allison Patterson, Author ACKNOWLEDGEMENTS I am deeply indebted to many people who have contributed to this study and my education in wildlife science. I would like to express my sincere appreciation to Dan Roby, my major advisor, for opportunities and support he has given me during the last five years. I also thank the other members of my graduate committee, Bruce Dugger, Matt Betts, and Milan Milovancev, for their time and input. Don Lyons and Rob Suryan, were not on my committee, but nonetheless contributed greatly to my research and general education. Funding for my research has come primarily from the U.S. Army Corps of Engineers, Portland District, coordinated by Paul Schmidt. This research would not have been possible without the support of the Klamath Basin National Wildlife Refuges, in particular Dave Mauser and John Beckstrand (USFWS). Ken Collis, Allen Evans, and Nathan Hostetter of Real Time Research, provided invaluable encouragement and support in the field. Thank you to the many people who provided field assistance and technical support, including: Dan Battaglia, Tim Lawes, Pete Loschl, Adam Peck-Richardson, William Mashburn, Kirsten Bixler, Yasuko Suzuki, Nicola Ventolini, Lydia Tiller, Meghan Horne-Brine, Katie Knox, and Allison Mohoric. I would also like to thank the other graduate students in the Roby lab, Dan Cushing, James Lawonn, Stefanie Collar, Tim Marcella, and Lindsay Adrean, who were always there to offer support and advice with the daily challenges of graduate school. I would like to thank my partner Darren Wiens for his support, encouragement, and patience over the last three years. Finally, I would also like to thank my parents, Karen Livingstone and Robert Patterson, and my brother Jesse Patterson for a lifetime of support. CONTRIBUTION OF AUTHORS Dr. Daniel D. Roby acquired funding, assisted with study design and interpretation of results, and provided editorial comments for all chapters. Dr. Donald E. Lyons provided training in field methods, and assisted with study design, data analysis, and interpretation of Chapters 2 and 3. Ken Collis acquired funding and assisted with logistics for Chapter 2. TABLE OF CONTENTS Page CHAPTER 1: GENERAL INTRODUCTION .............................................................. 1 LITERATURE CITED .......................................................................................... 9 CHAPTER 2: BREEDING ECOLOGY OF CASPIAN TERNS NESTING ON ARTIFICIAL ISLANDS IN THE UPPER KLAMATH BASIN, CALIFORNIA ...... 13 ABSTRACT ........................................................................................................ 14 INTRODUCTION ............................................................................................... 15 METHODS .......................................................................................................... 19 Study Area ................................................................................................ 19 Colony Size and Productivity................................................................... 21 Competition with Gulls ............................................................................ 24 Predation .................................................................................................. 25 Statistical Analysis ................................................................................... 27 RESULTS ............................................................................................................ 28 Caspian Tern Response to Habitat Creation and Social Attraction ......... 28 Colony Size and Productivity................................................................... 30 Competition with Gulls ............................................................................ 32 Water Availability .................................................................................... 34 Predation .................................................................................................. 35 DISCUSSION ...................................................................................................... 36 TABLE OF CONTENTS (Continued) Page LITERATURE CITED ........................................................................................ 46 CHAPTER 3: FORAGING BEHAVIOR OF CASPIAN TERNS NESTING AT TWO NEIGHBORING COLONIES ..................................................................................... 62 ABSTRACT ........................................................................................................ 63 INTRODUCTION ............................................................................................... 64 METHODS .......................................................................................................... 69 Study Area ................................................................................................ 69 GPS Tracking ........................................................................................... 69 Behavioral