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Grassland Birds in Natural and Cultivated Grasslands in the Northern Campos of Uruguay: Diversity Patterns, Responses to Vegetation Structure, and Nest Survival

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Grassland Birds in Natural and Cultivated Grasslands in the Northern Campos of Uruguay: Diversity Patterns, Responses to Vegetation Structure, and Nest Survival University of Missouri, St. Louis IRL @ UMSL Dissertations UMSL Graduate Works 7-17-2008 Grassland Birds in Natural and Cultivated Grasslands in the Northern Campos of Uruguay: Diversity Patterns, Responses to Vegetation Structure, and Nest Survival Adrian Bruno Azpiroz University of Missouri-St. Louis, [email protected] Follow this and additional works at: https://irl.umsl.edu/dissertation Part of the Biology Commons Recommended Citation Azpiroz, Adrian Bruno, "Grassland Birds in Natural and Cultivated Grasslands in the Northern Campos of Uruguay: Diversity Patterns, Responses to Vegetation Structure, and Nest Survival" (2008). Dissertations. 552. https://irl.umsl.edu/dissertation/552 This Dissertation is brought to you for free and open access by the UMSL Graduate Works at IRL @ UMSL. It has been accepted for inclusion in Dissertations by an authorized administrator of IRL @ UMSL. For more information, please contact [email protected]. University of Missouri-St. Louis Department of Biology Program in Ecology, Evolution and Systematics Grassland Birds in Natural and Cultivated Grasslands in the Northern Campos of Uruguay: Diversity Patterns, Responses to Vegetation Structure, and Nest Survival A Dissertation presented to the Graduate School of the University of Missouri-St. Louis in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biology By Adrián B. Azpiroz B.S., Biological Sciences, Facultad de Ciencias, Universidad de la República, 1996 M.S., Biology, Department of Biology, University of Missouri-St. Louis, 2004 Advisory Committee John G. Blake, Ph.D. (Advisor) Bette A. Loiselle, Ph.D. Robert E. Ricklefs, Ph.D. Peter D. Vickery, Ph.D. May 2008 Saint Louis, Missouri Adrián B. Azpiroz, 2008, Ph.D. Dissertation, p. i General Abstract Grassland bird populations are declining in many regions as a consequence of habitat modification and these declines have generated substantial effort to determine how grassland species cope with changes in habitat features, especially in agricultural landscapes. Grassland bird research has been concentrated in North America and Europe where changes in bird community composition and widespread species declines have been documented. In the Neotropical Region, however, many aspects of grassland bird ecology remain virtually unexplored. Avian communities currently associated with habitats that have experienced different land-use practices have not been fully characterized. The objective of this study was to examine the effects of habitat modification on the distribution, abundance, and reproductive success of grassland birds in the Northern Campos of Uruguay. The study focused on birds that inhabit four grassland habitats which differed in terms of agricultural management in the Northern Campos of Uruguay. Bird assemblages in croplands, planted pastures, and two natural grasslands under different grazing regimes were studied. First, distance sampling was used to characterize bird diversity patterns and population densities along the agricultural gradient. Second, nine vegetation structure variables were quantified and the response of birds species to these variables was assessed with multivariate analyses. Finally, systematic nest searching and monitoring activities were conducted during two breeding seasons and this information was used to estimate nest success patterns of both common and globally threatened species. Overall, a total of 50 species were recorded; cultivated and natural grasslands were dominated by grassland facultative and obligate species, respectively. Some threatened Adrián B. Azpiroz, 2008, Ph.D. Dissertation, p. ii species (Anthus nattereri, Sturnella defilippi) were largely restricted to natural grasslands. In terms of vegetation structure, grass cover and vegetation height were the two variables to which birds responded most strongly. With respect to nest survival, models that included temporal trends (i.e., seasonal effects) and habitat type effects were the ones best supported by the data. Nest survival of grassland birds was relatively low, but within the range documented in other grassland ecosystems. Contrary to expectation, nest survival of threatened taxa did not differ from that of common congenerics. This study is the first characterization of grassland bird communities inhabiting an agricultural landscape in the Northern Campos of Uruguay. Using modern sampling techniques and inferential procedures, information on bird diversity patterns and species- habitat relationships was combined with reproductive success data to provide a clear understanding of the effects of habitat alteration on grassland bird populations. The results from this study provide a useful baseline for the development of guidelines targeting bird conservation and land management in the grasslands of the Pampas region. Adrián B. Azpiroz, 2008, Ph.D. Dissertation, p. iii TABLE OF CONTENTS General Abstract…………………………………………………………………………...i Acknowledgments ………………………………………………………………………iv Chapter 1 Avian assemblages in altered and natural grasslands in the Northern Campos of Uruguay …………………………………………………………………………………...1 Chapter 2 Responses of grassland birds to variation in vegetation structure in the Northern Campos of Uruguay……………………………………………………………………...53 Chapter 3 Grassland bird nest survival in cultivated and natural grasslands of the Northern Campos of Uruguay……………………………………………………………………...93 Adrián B. Azpiroz, 2008, Ph.D. Dissertation, p. iv Acknowledgments I want to express my deep gratitude to John G. Blake for the great opportunity to study at UMSL and for his guidance and friendship during all these years. He always provided support and advice whenever I needed it, and this was particularly important while writing this dissertation. I am also very grateful to Bette A. Loiselle, Robert E. Ricklefs and Peter D. Vickery for their continued support and for reviewing my work, usually on very short notice. The comments, suggestions, and insight of all the members of my committee greatly improved the content of this dissertation. Adriana Rodriguez’s help and support was truly instrumental during all the phases of my dissertation, and I especially thank her for wise advice, guidance and companionship. I am also very grateful to Mauricio Bonifacino who kindly shared his expertise on Uruguayan vegetation and to Michael W. Palmer for assistance concerning ordination techniques. I also thank John T. Rotenberry and Thomas E. Martin who provided useful advice regarding vegetation sampling methods and nest success issues, respectively. Cintia Cornelius and Brandt Ryder shared their knowledge on nest survival software. During field work in Uruguay I received help from countless individuals. I am deeply indebted to José Pedro Castro and family, Guillermo Constantin, Marita Berretta, Arturo Menéndez, Eduardo Muguerza, Julio Obiague and Luis Baranov for granting permission to work on their lands. José Pedro Castro provided housing in many opportunities at Estancia El Tapado. Eva Mena, Ramón and Chito Nuñez, Familia San Martín, and Paco Larrosa assisted my team many times. I am especially grateful to Gustavo and Evangelina Battocletti for their friendship and for providing housing and Adrián B. Azpiroz, 2008, Ph.D. Dissertation, p. v helping with logistics during multiple visits to Estancia Cerro del Tesoro. Martín Echenique, Eva Mena, Nancy Rodríguez, Eduardo Goncálvez, Elba Leites and Miguel Echenique assisted with logistics at Cerros de Vera. I also sincerely thank Luis Bisio and Martín Toucon for logistic support at Estación Experimental de Facultad de Agronomía- San Antonio and Rafael and Juan Pablo Apatie for further assistance. I am very grateful to Mimosa and Pedro Azpiroz for their hospitality and assistance in Salto City and Colonia Itabepí, respectively. I am also deeply thankful to all field assistants and volunteers who dedicated so much time and effort to this project: Gonzalo Cortés, Ariel Ocampo, Evaristo Méndez, Ana Paula Blazina, Leandro and César A. Balbusso, Karen Alexander, Rocío Sánchez, Guillermo Barrenechea, Luciano Liguori, Carolina Abud, Andrea Lafranconi, Pablo Rocca, Juan Pedro Bouvet, Joaquin Aldabe, Diego Caballero, Natalia Zaldúa, Gonzalo Arnedillo, Verónica Trucco, María de la Paz Ducommun, Isabel López García, Pau Ferrer, Alvaro Vega, Mónica Búrmida, Francisco Encinas, Gisele Veiga, Felipe García Olaso and Patricia Arbiza. This research would not have been possible without their extraordinary commitment. Claudia D'Acunto assisted in spreading the word about the project in Argentina and Alejandro Fallabrino’s help, through the Ecovoluntarios network, guaranteed a large number of potential assistants. Adriana Rodriguez was in charge of the project during brief periods and she did an excellent job. Pablo Rodriguez provided his expertise (with excellent results) in the design of a poster and brochure that supported educational activities. I also thank the teachers at Vera school for their help with educational activities and Evaristo Méndez for his wonderful outreach work. Adrián B. Azpiroz, 2008, Ph.D. Dissertation, p. vi Financial support for this research was provided by Wildlife Conservation Society, Rufford Maurice Laing Foundation, Cleveland Metroparks Zoo and Cleveland Zoological Society's, Neotropical Grassland Conservancy, and Sigma Xi-The Scientific Research Society. Idea Wild and Neotropical Grassland Conservancy provided additional grants for field equipment. I sincerely thank Orietta Brewer, Avecita Chicchon, Felicity Arengo, Matthew O'Brien,
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