The Breeding Ecology of White-Faced Ibis in the Lower Carson River Basin, Nevada
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Louisiana State University LSU Digital Commons LSU Historical Dissertations and Theses Graduate School Fall 10-25-2000 The rB eeding Ecology of White-Faced Ibis in the Lower Carson River Basin, Nevada Eric Patrick Kelchlin Louisiana State University and Agricultural and Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_disstheses Part of the Forest Sciences Commons, and the Ornithology Commons Recommended Citation Kelchlin, Eric Patrick, "The rB eeding Ecology of White-Faced Ibis in the Lower Carson River Basin, Nevada" (2000). LSU Historical Dissertations and Theses. 8237. https://digitalcommons.lsu.edu/gradschool_disstheses/8237 This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Historical Dissertations and Theses by an authorized administrator of LSU Digital Commons. For more information, please contact [email protected]. THE BREEDING ECOLOGY OE WHITE-FACED IBIS IN THE LOWER CARSON RIVER BASIN, NEVADA A Thesis Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Master of Science in The School of Forestry, Wildlife and Fisheries By Eric Patrick Kelchlin B.S., Unity College, 1991 December 2000 MANUSCRIPT THESES Unpublished theses submitted for the Master’s and Doctor’s Degrees and deposited in the Louisiana State University Libraries are available for inspection. Use of any thesis is limited by the rights of the author. Bibliographical references may be noted, but passages may not be copied unless the author has given permission. Credit must be given in subsequent written or published work. A library which borrows this thesis for use by its clientele is expected to make sure that the borrower is aware of the above restrictions. LOUISIANA STATE UNIVERSITY LIBRARIES ACKNOWLEDGMENTS I am very grateful to Robert Bear, James Hall, Thomas Hook, Jill Keen, and Kristian McIntyre for their help in field efforts. Thanks to Bob Flores, Bill 1 lenry. Gary Ivey, Larry Neal, and Tara Zimmerman for providing technical assistance and logistical support during all phases of the study. Special thanks go to Dr. Vernon Wright for statistical and writing assistance, to Dr. Frank Rohwer, and Dr. Robert Hamilton for their insightful comments that improved the thesis. The research was funded by the U.S. Fish and Wildlife Service (Division of Migratory Birds and Habitat Programs, and Stillwater National Wildlife Refuge) and the Nevada Division of Wildlife. TABLE OF CONTENTS ACKNOWLEDGEMENTS.............................................................................................. ii ABSTRACT...................................................................................................................... iv CHAPTER 1. INTRODUCTION...................................................................................... 1 CHAPTER 2. POPULATION FLUCTUATIONS IN RELATION TO SURFACE WATER CONDITIONS........................................................................... 4 STUDY AREA.......................................................................................................6 MATERIALS AND METHODS.......................................................................... 6 RESULTS........................................................................................................... 10 DISCUSSION..................................................................................................... 18 CHAPTER 3. NESTING ECOLOGY............................................................................ 23 STUDY AREA.................................................................................................... 24 MATERIALS AND METHODS........................................................................ 26 RESULTS.............................................................................................................31 DISCUSSION...................................................................................................... 43 MANAGEMENT IMPLICATIONS................................................................... 49 CHAPTER 4. NEST AND COLONY SITE SELECTION...........................................51 STUDY AREA.....................................................................................................52 MATERIALS AND METHODS........................................................................ 53 RESULTS.............................................................................................................58 DISCUSSION.......................................................................................................65 MANAGEMENT IMPLICATIONS................................................................... 68 CHAPTER 5. SUMMARY AND CONCLUSIONS...................................................... 69 POPULATION FLUCTUATIONS IN RELATION TO SURFACE WATER CONDITIONS......................................................................................................69 NESTING ECOLOGY.........................................................................................71 NEST AND COLONY SITE SELECTION........................................................ 73 REFERENCES................................................................................................................. 74 VITA 85 ABSTRACT The Great Basin White-faced Ibis (Plegadis chihi) population is recognized as a Species of Management because of its small population size, limited number of traditional breeding sites, and vulnerability to habitat loss. The ability to predict future population trends and develop wetland management strategies is limited because many aspects of their breeding ecology and population dynamics are unknown. 1 examined White-faced Ibis nesting ecology and breeding habitat selection at the Lower Carson River Basin, Nevada, from 1995-1997, and the relationship between the local surface water conditions and trends in the number of breeding pairs from 1970-1997 on a local and regional scale. Reproductive success was highly variable among colonies (n=20) and years. Seasonal trends in nest success and clutch size were evident during each year of the study. Predation, weather exposure, and human disturbance accounted for the majority of nest failures. Nest height above the water’s surface was the only nest site attribute that clearly affected nest success. White-faced Ibis nested indiscriminately within stands of emergent vegetation and did not appear to use microhabitat preferences to select colony or nest sites. Habitat plasticity in colony and nest site selection may provide a selective advantage in unstable wetland habitats. The criteria used to evaluate nesting habitat may pertain to the social aspects of colony formation. The number of breeding pairs in the Lower Carson River Basin was positively related to local surface water conditions. May of the current year, and May-August and October of the previous year explained 71.2% of the variation in the number of breeding pairs. Surface water conditions in the Lower Carson River Basin were not correlated with fluctuations in the number of breeding pairs at Malheur National Wildlife Refuge in Oregon. CHAPTER 1. INTRODUCTION The White-faced Ibis (Plegadis chihi) is a colonial waterbird that breeds in western North America and southern South America (Ryder 1967). Within North America, large numbers arc found along the Texas and Louisiana coasts and in the Great Basin states of Nevada and Utah, with peripheral but grow ing colonies in Oregon. Idaho, and California (Ryder and Manry 1994). In addition, small numbers nest sporadically in Colorado. Wyoming, Montana. North and South Dakota, southern Alberta, Iowa, and Oklahoma (Ryder and Manry 1994, Ivey et al. in prep). White-faced Ibis breeding in the Great Basin and surrounding area (designated as the Great Basin population) are recognized as a Species ot Management Concern (USFWS 1995a) because of the small population size, limited number of traditional breeding sites, and vulnerability to habitat loss. The Great Basin White-faced Ibis population averaged 26,000 breeding pairs from 1997 to 1999 (Ivey et al. in prep), which is triple the 1984 estimate of 7,500 breeding pairs (Sharp 1985). Although the population has grown substantially over the last two decades, the ability to predict future population trends is limited because many aspects of their breeding ecology and population dynamics are unknown. Wetland communities within the Great Basin undergo changes within and among seasons due to water level fluctuations that vary in magnitude, timing, frequency, and duration (Jehl 1994, Earnst et al. 1998. Warnock et al. 1998). White faced Ibis exploit unpredictable habitat conditions by relocating within and between watersheds when local breeding habitat conditions deteriorate (Ryder 1967, Sharp 1985, Ivey et al. 1988. Henny and Herron 1989, Earnst et al. 1998). This nomadic breeding 1 strategy may promote population stability and growth if alternative wetland breeding sites are available (Vance 1980, Den Boer 1981, Bessenger 1986. Benetts and Kitchens 1997). The availability of refugia is especially critical when droughts and floods render traditional breeding sites unsuitable for nesting (Eamst et al. 1998). Traditional breeding sites such as the Lower Carson River Basin in northwest Nevada. Malheur NWR in southeast Oregon, and Great Salt Lake in northern Utah, annually