DOES MIGRATION MATTER? CAUSES AND CONSEQUENCES OF MIGRATORY BEHAVIOR IN SIERRA NEVADA BIGHORN SHEEP By DEREK BENJAMIN SPITZ B. A. Biology, University of Chicago, Chicago, IL, 2009 Dissertation presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Fish and Wildlife Biology The University of Montana Missoula, MT December 2015 Approved by: Sandy Ross, Associate Dean of The Graduate School Graduate School Mark Hebblewhite, Chair Dept. of Ecosystem and Conservation Science, Wildlife Biology Program, University of Montana Winsor H. Lowe Dept. of Ecosystem and Conservation Science, Wildlife Biology Program, University of Montana L. Scott Mills Dept. of Forestry and Environmental Resources, College of Natural Resources, North Carolina State University Michael S. Mitchell Dept. of Ecosystem and Conservation Science, Wildlife Biology Program, University of Montana Thomas R. Stephenson California Department of Fish and Game © COPYRIGHT by Derek Benjamin Spitz 2015 All Rights Reserved Spitz, Derek, Ph.D, Fall 2015 Fish and Wildlife Biology Does migration matter? Causes and consequences of migration in Sierra Nevada bighorn sheep Chair: Mark Hebblewhite Despite their potential conservation importance, the demographic implications of migratory behavior remain poorly understood. Sierra Nevada bighorn sheep (Ovis canadensis sierrae; hereafter “Sierra bighorn”) are federally-endangered and partially migratory. In summer, Sierra bighorn share high-elevation summer ranges, but in winter some individuals migrate to lower elevation for winter while others remain resident at high-elevation. Lower elevations have better forage in winter, but these areas also carry an increased risk of predation from Sierra bighorn's primary predator, the cougar (Puma concolor). We should therefore expect differences in winter conditions to result in demographic differences between migrants and residents. First, I developed new software tools in an open-source R package ‘migrateR’ for classifying migratory behavior, including novel techniques for identifying altitudinal migration. Applying these tools to Sierra bighorn showed that migratory behavior in this taxon is extremely flexible in both status (migrant v. resident) and tactics (e.g. timing, duration of movements), with individuals frequently switching migratory status between years. I tested for status-specific differences in winter resource use and selection by migrants and residents using resource selection functions across three scales. Migrants and residents showed scale-specific differences in resource selection offering contrasting solutions to a forage-predation tradeoff. Residents avoided predation risk at the coarsest scale, but focused on forage in fine-scale selection, whereas migrants selected for forage at the coarsest spatial scale and focused on avoided predation risk at finer scales. This pattern of selection resulted in migrants gaining better access to forage. The amount of migrant habitat predicted differences in the prevalence of migration across eight populations. Lastly, I tested causes and consequences of migratory behavior in Sierra bighorn. Migratory propensity increased with winter severity. Individuals that were still lactating in fall were highly likely to migrate, but the strength of this effect declined with body mass. I failed to find an effect of winter elevation on adult female survival. Finally, Sierra bighorn were more likely to be observed with a lamb following residency than following migration. These results suggest that where residency is viable, residents make greater per-capita contributions to population growth than do migrants. iii ACKNOWLEDGEMENTS Fully enumerating the gratitude I feel for the past four and a half years borders on impossibility. The years have been full. Above all, I am indebted to Dr. Mark Hebblewhite for his generosity and dedication as an advisor and mentor. Mark consistently showed great patience in allowing me the freedom to make the mistakes I needed while showing tremendous kindness in warning me against following certain rabbit holes too far down. I am similarly indebted to Dr. Tom Stephenson for his continuing guidance and encouragement since entering the wildlife field. I blame Dr. Kevin Monteith for the discovery of a field that I love. This research would be impossible without the tenacious field efforts of the California field team, which has been built by the epic effort of Todd Calfee, Alex Few, Kelsey Ellis, Jonathan Fusaro, Brian Hatfield, Armin Howell, Dennis Jenson, Kathleen Knox, Julia Runcie, and Ryan Spaulding. Heather Johnson was the first to train me for work with bighorn and to suggest I consider returning to school. Lacey Greene first introduced me to the analytical challenges of graduate research. Dave German gave me an invaluable early lesson on the folly of technophobia. Heather Johnson was the first to train me in observing bighorn and to suggest I consider returning to school. I thank John Wehausen for his love of observation, enthusiasm for the scientific process and eagerness to share knowledge hard-earned. I cannot express the extent to which my intellectual growth is indebted to fellow graduate students, particularly members of the Heblab past and present: Sonja Christensen, Nick DeCesare, Dan Eacker, Scott Eggeman, Josh Goldberg, Lacey Greene, Nicole Hupp, Mark Hurley, Andrew Jakes, Clayton Miller, Robin Steenweg, Tshering Tempa and especially Wibke Peters. Joe Smith and Mike LeMoine also provided collaboration and humor at several key junctures. There are many others at the university deserving special thanks, especially my committee members, Drs. Winsor Lowe, L. Scott Mills and Michael Mitchell, who provided valuable feedback on much of what follows. Josh Nowak entertained questions of varying scope with kindness and characteristic patience. Catherine Redfern and Jim Adams made the otherwise onerous tasks of hiring and grant management a true pleasure. Like many before me, I've depended on Jeanne Franz's guidance. As we all know, she is an unstoppable force of helpfulness. With time I have come to increasingly appreciate the profound influence of my friends and family. I thank my father for introducing me to the mountains and showing me that you can follow your recreation into a fulfilling career and thank my mother for helping me learn that a compass is only useful if you don't know where you're going. I am also most grateful for the acceptance and support of my new family Sharon, Frank and Hannah as well as my wife Emma. Emma's irrepressible kindness, curiosity and laughter have become one of my life's few constants. I cannot appreciate enough the sense of stability these landmarks provide. Finally I thank the communities of friends who have made me feel at home in Bishop, Fort Collins and Missoula. Financial support for this research was provided by the California Department of Fish and Wildlife. iv TABLE OF CONTENTS ABSTRACT....................................................................................................................... iii ACKNOWLEDGEMENTS................................................................................................iv LIST OF TABLES............................................................................................................viii LIST OF FIGURES.......................................................................................................... xiii CHAPTER 1. Introduction and Overview...........................................................................1 Dissertation Format.........................................................................................................7 References.......................................................................................................................8 CHAPTER 2. "migrateR": Extending non-linear modeling methods for quantifying migratory movement behavior........................................................................................... 11 Methods.........................................................................................................................14 Adaption of NSD Models.........................................................................................14 Adapted Elevation Models....................................................................................... 16 Sensitivity to Start Date............................................................................................17 Example: Elk and Bighorn Sheep............................................................................ 19 Discussion..................................................................................................................... 22 References.....................................................................................................................27 CHAPTER 3. How plastic is migratory behavior in Sierra Nevada Bighorn Sheep?.......43 Materials and Methods..................................................................................................47 Study Area................................................................................................................ 47 Location Data........................................................................................................... 49 Modeling Altitudinal Movement..............................................................................49 Statistical Analyses...................................................................................................53