REPRODUCTIVE SUCCESS OF GREATER SANDHILL CRANES (ANTIGONE CANADENSIS TABIDA) AT HORICON MARSH, WISCONSIN By Sabine Y. Berzins A Thesis Submitted in partial fulfillment of the requirements of the degree MASTER OF SCIENCE IN NATURAL RESOURCES (WILDLIFE) College of Natural Resources UNIVERSITY OF WISCONSIN Stevens Point, Wisconsin December 2020 APPROVED BY THE GRADUATE COMMITTEE OF: Dr. Shelli A. Dubay Professor of Wildlife Dr. Jason D. Riddle Professor of Wildlife Dr. Benjamin S. Sedinger Assistant Professor of Wildlife Anne E. Lacy Senior Manager – North America Programs, International Crane Foundation Sadie L. O’Dell Wildlife Biologist, Horicon National Wildlife Refuge ii ABSTRACT Greater sandhill cranes (Antigone canadensis tabida) and endangered whooping cranes (Grus americana) share many life history traits. Therefore, evaluating sandhill crane productivity in certain locations could be an indicator of future whooping crane breeding success. Since 2011, captive-reared whooping cranes have been released at Horicon Marsh in Dodge County, Wisconsin, adding to the reintroduced Eastern Migratory Population. However, reproductive success of this population has remained low. Few whooping cranes spend the breeding season at Horicon Marsh, so questions remain as to whether whooping cranes can nest and raise young successfully at Horicon. To reevaluate Horicon Marsh as a release area for whooping cranes, I studied nest density and success as well as colt survival of sandhill cranes at Horicon Marsh. Fifty-seven nests were detected via aerial surveys during 2018–2019. Detection probability was estimated to be 66% using a closed-population mark-recapture method. Nest densities (0.64 nests/km2) were lower than reported in other studies. Using trail cameras, I estimated nest success of 36 sandhill crane nests. Both apparent nest success (0.82) and daily nest survival (0.991) were high compared to other published estimates. Colt survival was estimated by tracking family groups where one adult was radio marked to determine the fate of the colt(s). Colts were estimated to have a 3% chance of surviving to fledge. My results suggest that availability of nesting habitat and nest success were not limiting sandhill crane productivity at Horicon Marsh. However, colt survival may be too low to contribute to the growth of the sandhill crane population, raising questions about the potential for reproductive success for cranes of either species at Horicon Marsh. iii ACKNOWLEDGMENTS This research was made possible through support from the International Crane Foundation, the University of Wisconsin—Stevens Point, and the U.S. Fish and Wildlife Service. The project and my writing were improved by the contributions of my committee members, Shelli Dubay, Jason Riddle, Anne Lacy, Sadie O’Dell, and Ben Sedinger. I would like to thank Shelli and Jason, my co-advisors, for taking me on as a graduate student, helping to fund my position, and for their trust and support over the years. Anne initiated this project, and I am so grateful to have had the opportunity. Sadie went above and beyond at Horicon NWR and for me personally—thank you for being a wonderful summer roommate. I am glad to have learned a great deal from Ben’s expertise on wetlands and waterfowl. I would like to thank the Horicon National Wildlife Refuge staff, especially Sadie, Jon Krapfl, Bill Peterson, and Dave Bolin for sharing vehicles, equipment, and their invaluable knowledge of the Refuge. Paul Samerdyke and Chris Cole from Horicon Marsh Wildlife Area were always willing to answer questions and provide logistic support. It was my pleasure to work with Nora Hargett, who was extremely competent and positive at all times. I would also like to thank Renee Wahlen, Marsh Haven Nature Center, and the Friends of Horicon National Wildlife Refuge for providing field housing for Nora. Andy Gossens from ICF did much of my fieldwork with me, and I truly could not have done this project without him. Thanks also to Bob Bergstrom, who was a dedicated volunteer and great communicator. My friend and lab mate Ross McLean also volunteered his time to help me in the field. Sadie, Jon, and Anne deserve extra thanks as they also spent significant time helping with fieldwork. iv I am also grateful to many people outside of Horicon who supported this research. David Moore generously donated the helicopter flights; a huge thank you goes to Todd Chilton and Brian Richter, the expert pilots who flew the surveys. Suzanne Johnson supported my internship at ICF. Davin Lopez and Liz Smith provided trail cameras. I learned so much from Brad Strobel, Jeff Fox, and Ross McLean during my time at Necedah NWR. Thanks also to the ICF folks who first introduced me to crane research, especially Dorn Moore, Hillary Thompson, Anne, Andy, and, of course, Dr. George Archibald. George suggested that I take on this project, and I am so thankful for his kindness and guidance. And, last but not least, thanks to my parents for supporting me always. v TABLE OF CONTENTS ABSTRACT ................................................................................................................... iii ACKNOWLEDGMENTS .............................................................................................. iv TABLE OF CONTENTS ............................................................................................... vi LIST OF TABLES ....................................................................................................... viii LIST OF FIGURES ......................................................................................................... x PREFACE ...................................................................................................................... xi CHAPTER 1: SANDHILL AND WHOOPING CRANES—BACKGROUND AND LITERATURE REVIEW ....................................................................................................1 INTRODUCTION ........................................................................................................... 1 Justification .................................................................................................................. 1 Historic recovery of sandhill and whooping crane populations .................................. 2 Previous research at Necedah National Wildlife Refuge, Wisconsin ......................... 5 Shifting the release area of EMP whooping cranes to eastern Wisconsin ................... 7 Sandhill cranes as a substitute species for whooping cranes ....................................... 9 Sandhill and whooping cranes at Horicon Marsh ...................................................... 13 LITERATURE CITED ................................................................................................. 14 CHAPTER 2: SANDHILL CRANE NEST DETECTION AND AVAILABILITY OF NESTING HABITAT ........................................................................................................20 INTRODUCTION ......................................................................................................... 20 METHODS.................................................................................................................... 24 Study area .................................................................................................................. 24 Helicopter surveys of nests ........................................................................................ 25 Calculation of detection probability .......................................................................... 27 Calculation of nest density ........................................................................................ 28 Classifying cattail landcover at Horicon NWR ......................................................... 29 RESULTS...................................................................................................................... 32 Probability of nest detection and estimated abundance ............................................. 32 Nest density ............................................................................................................... 33 Supervised classification of Horicon NWR ............................................................... 34 DISCUSSION ............................................................................................................... 35 Nest detection and estimates of abundance ............................................................... 35 Nest density ............................................................................................................... 37 Survey coverage ........................................................................................................ 38 Availability of nesting habitat ................................................................................... 39 vi Management implications ......................................................................................... 42 LITERATURE CITED ................................................................................................. 44 CHAPTER 3: SANDHILL CRANE NEST SUCCESS AND COLT SURVIVAL AT HORICON MARSH, WI ...................................................................................................57 INTRODUCTION ......................................................................................................... 57 STUDY AREA .............................................................................................................. 61 METHODS...................................................................................................................