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Roost Site Selection of Dunlin (Calidris ROOST SITE SELECTION OF DUNLIN (CALIDRIS ALPINA) ON ARCATA BAY, HUMBOLDT BAY, HUMBOLDT COUNTY CALIFORNIA by Tia L. Adams A Thesis Presented to The Faculty of Humboldt State University In Partial Fulfillment Of the Requirements for the Degree Masters of Science In Natural Resources: Wildlife November, 2011 ABSTRACT Roost Site Selection of dunlin (Calidris alpina) on Arcata Bay, Humboldt Bay, Humboldt County, California Tia Adams I examined the relationship between nonbreeding dunlin (Calidris alpina) roost use on Arcata Bay and energy balance (proximity hypothesis), predation, and predation risk. Individuals used roosts that were closer to their last foraging locations than roosts that were known to them and roosts that were available to the population. These findings are similar to findings on temperate and tropical bays as well as those derived from models. Predation danger and predation avoidance, two complementary factors included in the predation risk analysis, influenced dunlin roost use at high tide. Individuals were likely to abandon their roost during the observation period if the initial flock size was high. Conversely, they did not return to the roost the following day if the number of attacks sustained at the roost was low and if the final flock size from the previous day was low. Individuals consistently selected roosts that had higher initial flock sizes as well as higher numbers of attacks, successful attacks, and predators present. These results suggest that individuals are making daily decisions regarding their roost use and basing those decisions on the need to minimize energy as well as reduce their predation risk. iii ACKNOWLEGDMENTS I thank my advisor Dr. M.A. Colwell and my committee members Drs. M. D. Johnson and T. L. George for their invaluable time and assistance in this endeavor. I would like to thank Jesse Conklin for radio-marking all of the dunlin and collecting additional data and Mark Colwell and Jason Meyer for collecting additional field data during my project. I am very appreciative to Dr. Bill Bigg for always making time to answer my statistics questions. Funding was provided by the California Department of Fish and Game’s Oil Spill Response Trust Fund through the Oiled Wildlife Care Network at the Wildlife Health Center, School of Veterinary Medicine, University of California, Davis and The Arcata Marsh Project. I am indebted to ABR, Inc for allowing me access to their Information Technology (IT) and office space. I am especially indebted to the Bureau of Land Management, Arcata Field Office and the Klamath Falls, Office of the U.S. Fish and Wildlife Service for encouraging me throughout this process. I wish to thank my friends Jon Plissner and Josh Rasmussen for reading lots of iterations of this project, being constant sources of encouragement, and endless amounts of information. I am forever grateful to Peter Sanzenbacher for his advice, time, patience, understanding, and encouragement; it was always a pleasure to pick your brain. To Roxy and Louie for enduring days without long walks, those days are finally gone. To my family without whom none of this would be possible, you are the most amazing people on the planet. iv TABLE OF CONTENTS ABSTRACT ....................................................................................................................... iii ACKNOWLEGDMENTS ................................................................................................. iv TABLE OF CONTENTS .................................................................................................... v LIST OF TABLES ............................................................................................................. vi LIST OF FIGURES .......................................................................................................... vii LIST OF APPENDICES .................................................................................................. viii INTRODUCTION .............................................................................................................. 1 MATERIALS AND METHODS ........................................................................................ 6 Study Area ...................................................................................................................... 6 Field methods, Data Summary and Analysis .................................................................. 8 RESULTS ......................................................................................................................... 15 DISCUSSION ................................................................................................................... 25 LITERATURE CITED ..................................................................................................... 31 v LIST OF TABLES Table Page 1 The coefficients of the logistic regression models comparing whether an individual abandoned (0) or utilized (1) its roost during its observation period. ..........................18 2 AIC values for the abandonment models: “abandoned or stayed at its roost during its observation period” and “abandoned or utilized its roost from the prior observation period.” FlockI represents initial flock size, while FlockF indicates final flock size, Pred is the total number of predators observed, AttacksT is the total number of attacks, AttacksS is the number of successful attacks, and Raptor indicates Presence or absence of a raptor predator. ........................................................................................19 3 The coefficients of the logistic regression models comparing whether an individual abandoned (1) or utilized (0) its roost from the prior observation period. ..................20 vi LIST OF FIGURES Figure Page 1 Location of Arcata Bay in Humboldt County, California..............................................7 2 Locations of roosts used by monitored dunlin wintering on Humboldt Bay, California, December 1, 2004 - March 16, 2005 (Conklin and Colwell 2007). Five most used roosts on Arcata Bay: Klopp Lake (53), Indianola (63), Mad River Slough (32), the Mad River Slough pastures (36), and Vance Road (81) (Colwell et al. 2003). ...........13 3 Foraging locations ● of wintering dunlin on Arcata Bay, Humboldt County, California, December 1, 2004 - March 16, 2005. Jacoby Creek, the most used last foraging location, is identified on the right. .................................................................16 4 The initial flock size of roosts selected by radio-marked dunlin compared to random roosts in Arcata Bay relative to whether an individual abandoned or stayed at its roost. The differences in sample sizes are due to the days when multiple individuals were tracked. Bars indicate the mean number of attacks, while the whiskers are one Standard Error (SE)......................................................................................................21 5 The number of attacks by avian predators at roosts that were selected by focal dunlin as compared to random roosts on Arcata Bay relative to whether an individual abandoned or stayed at its roost. The differences in sample sizes are due to the days when multiple individuals were tracked. Bars indicate the mean number of attacks, while the whiskers are one Standard Error (SE). .........................................................22 6 The number of successful attacks at the roosts selected by radio-marked dunlins as compared to random roosts on Arcata Bay relative to whether an individual abandoned or stayed at its roost. The differences in sample sizes are due to the days when multiple individuals were tracked. Bars indicate the mean number of attacks, while the whiskers are one Standard Error (SE). .........................................................23 7 The final flock size of roosts selected by radio-marked dunlin compared to random roosts on Arcata Bay relative to whether an individual abandoned or stayed at its roost. The differences in sample sizes are due to the days when multiple individuals were tracked. Bars indicate the mean number of attacks, while the whiskers are one Standard Error (SE)......................................................................................................24 vii LIST OF APPENDICES Appendix Page A. Individual radio-marked dunlin and their successive diurnal roost use over their radio- life days during the winter study of 2004-2005 on Humboldt Bay, California. One through 38 indicate the number of radio days individuals were tracked. ....................36 B. Number of roosts used in one observation period by an individual monitored, radio- marked dunlin their radio-life days during the winter of 2004-2005 on Humboldt Bay, California. Day one occurs on the first day of trapping. One through 38 indicate the number of radio days individuals were tracked. ..........................................................38 viii INTRODUCTION Roosts, locations where individuals concentrate when they are not feeding or breeding (Hockey 1985), are an integral facet of the nonbreeding ecology of shorebirds (suborder: Charadrii) (Hale 1980). Roosts are especially important in coastal regions where high tides predictably inundate principal foraging habitats and force birds onto higher ground until the tides ebb and their principal foraging habitat becomes available again (Hale 1980, Colwell et al. 2003, Conklin and Colwell 2007). Individuals may spend a significant portion of their time resting, preening, supplemental feeding, or
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