SPACE USE OF AMERICAN AVOCETS (RECURVIROSTRA AMERICANA) IN SOUTH SAN FRANCISCO BAY, CALIFORNIA by Scott A. Demers A Thesis Presented to The Faculty of Humboldt State University In Partial Fulfillment Of the Requirements for the Degree Master of Science In Natural Resources: Wildlife August, 2007 ABSTRACT Space Use of American Avocets (Recurvirostra americana) in South San Francisco Bay, California Scott A. Demers Examining the spatial ecology of waterbirds is essential for the conservation and management of wetland areas. I studied the space use (movements and home ranges) of radio-marked female American avocets (Recurvirostra americana) in South San Francisco Bay, California. Direct visual observations were used to determine the breeding stage (pre-incubation, incubation, brood-rearing, post- breeding) of marked avocets. Linear movements, home ranges, core areas, and average distances of avocets from nests varied significantly among stages. Post-breeding space use metrics were the greatest, followed by pre-incubation, incubation, and brood-rearing. The majority of avocet nest locations (93%) were within the pre-incubation core area boundaries, whereas 36% of nests were within post-breeding core areas. Distance between future nest sites and daily location decreased significantly with number of days prior to incubation. The differences in home ranges, core areas, and movements between the pre- incubation and post-breeding stages suggest space use of female avocets may be influenced by breeding activities. Average distance from nest during the pre- incubation stage suggests that avocets may be prospecting future nest sites up to three iii weeks prior to nesting. In a highly managed estuary like the San Francisco Bay, natural resources managers can utilize spatial data and implement conservation strategies that maximize the potential for continued survival of American avocets and other breeding waterbirds. iv ACKNOWLEDGMENTS This research was funded by the CalFed Bay-Delta Program’s Ecosystem Restoration Project. Thanks to Dr. John Takekawa, Dr. Josh Ackerman, and all the members to the CalFed mercury project team that graciously allowed graduate students to be a part of the project. Thanks to committee members Dr. Rick Golightly and Dr. Matt Johnson for sharing their input and experience. I owe special thanks to Dr. Mark Colwell for advising me through thick and thin. I would like to thank Jill Bluso, Stacy Moskal, Brooke Hill, Joe Northrup, Kristen Dybla, Lindsay Dembosz, Emily Eppinger, River Gates, Angela Rex, Mychal Truwe, and Ross Wilming for hard work and dedication to this project. I also thank Clyde Morris and the staff at the Don Edwards San Francisco Bay National Wildlife Refuge for logistical support. v TABLE OF CONTENTS Page ABSTRACT ………..…………………………………………………………….. iii ACKNOWLEDGMENTS ………………………………………………………… v LIST OF TABLES ………...……………………………………………………… vii LIST OF FIGURES …………..………………………………………………….. viii LIST OF APPENDICES ……………...…………………………………………... ix INTRODUCTION ……………...……………………………………………….... 1 STUDY AREA …………………………………...………………………………. 3 METHODS ……………………...………………………………………………... 5 Capture and Radio Telemetry ……...……………………………………... 5 Data Summary and Analysis …………...…….…………………………… 7 RESULTS …………………..…………………………………………………….. 10 Linear Movements and Home Range …………..………………………… 10 Behavior and Flock Size ……………………..…………………………… 17 DISCUSSION ……………………………………..……………………………… 19 Conservation Implications ………..……………… ……………………… 21 LITERATURE CITED …………………..……………………………………….. 24 APPENDIX A ………………..…………………………………………………… 29 APPENDIX B ………………..…………………………………………………… 30 APPENDIX C …………..………………………………………………………… 31 vi LIST OF TABLES Table Page 1 Recorded behaviors of radio-marked American avocets in in South San Francisco Bay, California, USA. Behaviors were recorded opportunistically when individuals could be visually located .…………………………………………………………….….. 18 . vii LIST OF FIGURES Figure Page 1 Map of South San Francisco Bay, California, showing dominant habitat types and American avocet capture locations in 2005 and 2006. Avocets were captured in two salt ponds (Ponds A8 and A16) and a tidal flat (Coyote Creek Lagoon) ...……………………………………...……..…...... 4 2 Mean (± SE) linear distance between consecutive locations of American avocets in South San Francisco Bay, California, USA, 2005-06 ……..….… 11 3 Mean (± SE) home range size and linear movements of four American avocets sampled in each breeding stage in South San Francisco Bay, California, USA, 2005-06. Standardized scores were calculated based on individual mean values across the four stages .....………………..….…. 12 4 Mean (± SE) home range and core area size of American avocets in South San Francisco Bay, California, USA, 2005-06 …………………...… 13 5 Mean (± SE) distances from nest location, in each breeding stage, of American avocets in South San Francisco Bay, California, USA, 2005-06 ..………………………………………………………………….. 15 6 Relationship between average (± SE) distances from nest and days prior to incubations during the pre-incubation stage for American avocets in South San Francisco Bay, California, USA, 2005-06 ...…………………… 16 viii LIST OF APPENDICES Appendix Page A The distance and time between consecutive locations, in each breeding stage, of American avocets in San Francisco Bay, California, USA. The fitted lines indicate there is no correlation in the time between locations and the distances moved (Pre-incubation, r2 = 0.01, P = 0.02; Incubation, r2 = 0.00, P = 0.892; Brood-rearing, r2 = 0.01, P = 0.420, Post-breeding, r2 = 0.0150, P = 0.031). All locations >1 hour apart were used for analyses ..................................……………………………...……………….29 B Average distances between consecutive locations of American avocets in each breeding stage, San Francisco Bay, California, USA. To test for temporal autocorrelation in linear movement data, locations less than 1, 2, 4, 8, and 16 hours apart were consecutively removed from analysis. These removals did not significantly alter average distance calculations; therefore all locations > 1 hour apart were used for analyses ………………...……... 30 C Average home range sizes of four American avocets in South San Francisco Bay, California, USA. Locations were randomly selected and removed to test for the minimum number of locations necessary to estimate home range size in each stage. The number of locations was visually determined to be 10 …………...……………………………………...….… 31 ix INTRODUCTION Investigating factors that influence space use of avian species is necessary to understand how they utilize habitats, when those areas are important to their survival, and when populations may be at risk. Recent studies have demonstrated that breeding stages can influence space use of avian species. Roth et al. (2004) found that common ravens (Corvus corax) remained closer to the nest during the incubation and nestling stages than in the pre-incubation period, and core areas were centered around nest sites and food sources. Home ranges and movements of golden eagles (Aquila chrysaetos) were larger during the non-breeding than breeding season (Marzluff et al. 1997). Willets (Tringa semiplamata) and killdeer (Charadrius vociferus) remained closer to their nesting areas while breeding than in the post-breeding stage (Haig et al. 2002, Plissner et al. 2000a). Killdeer also moved greater distances during the non-breeding stages than during the nesting stage (Plissner et al. 2000a). However, previous studies of breeding stage and space use in shorebirds (Plissner et al. 2000a, Haig et al. 2002) have not separated brood-rearing from the post-breeding stage, leading to the assumption that there is no difference in space use between these two stages. Since shorebird species care for precocial chicks after hatching (Lack 1968), space use during the brood-rearing period may be different and should be treated as a distinct stage. To our knowledge, no study has examined shorebird space use within four breeding stages (pre-incubation, incubation, brood-rearing, and post-breeding), likely due to the logistical difficulties of capturing non-breeding birds and obtaining visual 1 2 confirmation of each stage. Space use data in each breeding stage may be utilized by resource managers, as contaminant exposure and other population risks may vary with stage. Wetland-dependent species, like the American avocet (Recurvirostra americana), are often considered priorities for conservation and management due to habitat degradation and loss (Frayer et al. 1983, Dahl 1990, Catallo 1993, Plissner et al. 2000a). San Francisco Bay estuary, California is an important region for wintering and breeding avocets (Rintoul et al. 2003). However, avocet populations in this estuary may be at risk due to the presence of environmental contaminants, increases in California gull (Larus californicus) populations, and conversion of habitat. Understanding the space use requirements of American avocets may be beneficial for natural resources managers to minimize and mitigate these threats. Therefore, this study examined how space use varies across four stages of the annual cycle: pre-incubation, incubation, brood-rearing, and post-breeding. STUDY AREA San Francisco Bay, located in central California, is one of the largest estuaries on the Pacific coast of North America (Conomos 1979, Monroe & Kelly 1992). The study was conducted in the South San Francisco Bay (Fig. 1), which is defined as the region south of the San Mateo Bridge. South San Francisco Bay includes tidal flats and sloughs, tidal marshes, salt evaporation ponds, and