Testing the Function of Song Type Repertoires in Rock Wrens Using Playback Experiments and Behavioral Observations
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University of Northern Colorado Scholarship & Creative Works @ Digital UNC Dissertations Student Research 5-2018 Why Sing so Many Songs? Testing the Function of Song Type Repertoires in Rock Wrens Using Playback Experiments and Behavioral Observations Stephanie Marie Gobert Pitt Follow this and additional works at: https://digscholarship.unco.edu/dissertations Recommended Citation Pitt, Stephanie Marie Gobert, "Why Sing so Many Songs? Testing the Function of Song Type Repertoires in Rock Wrens Using Playback Experiments and Behavioral Observations" (2018). Dissertations. 510. https://digscholarship.unco.edu/dissertations/510 This Text is brought to you for free and open access by the Student Research at Scholarship & Creative Works @ Digital UNC. It has been accepted for inclusion in Dissertations by an authorized administrator of Scholarship & Creative Works @ Digital UNC. For more information, please contact [email protected]. © 2018 STEPHANIE MARIE GOBERT PITT ALL RIGHTS RESERVED UNIVERSITY OF NORTHERN COLORADO Greeley, Colorado THE GRADUATE SCHOOL WHY SING SO MANY SONGS? TESTING THE FUNCTION OF SONG TYPE REPERTOIRES IN ROCK WRENS USING PLAYBACK EXPERIMENTS AND BEHAVIORAL OBSERVATIONS A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science Stephanie Marie Gobert Pitt College of Natural and Health Sciences School of Biological Sciences M.S. Biology May 2018 ABSTRACT Pitt, Stephanie G. Why Sing So Many Songs? Testing the Function of Song Type Repertoires in Rock Wrens Using Playback Experiments and Behavioral Observations. Unpublished Master of Science Thesis, University of Northern Colorado, 2018. Bird song has been studied extensively as a model of complex animal communication systems because of how various and flexible it is in certain species. Numerous researchers have investigated the evolutionary pressures leading to the elaboration of songs available in a bird’s repertoire and this topic is most often evaluated in light of sexual selection. Intersexual selection mechanisms such as female choice are often presumed to be very important in the elaboration of song, however literature reviews on the topic find no strong correlation between female preference for larger song repertoires and the presence of the characteristic in males across all species. Another important aspect of sexual selection not often examined in regards to avian song elaboration is intrasexual selection mechanisms such as territory defense and within-sex competition. In no single study were both mechanisms of selection on a trait evaluated within the same individuals, though some studies have independently looked at both aspects in the same species. In this study I evaluated the function of song type repertoire size in a monomorphic species, the Rock Wren, in light of both inter- and intrasexual selection. To test the function of song type repertoire in territory defense contexts, I performed playback experiments to focal male Rock Wrens and assessed their response patterns to both large and small repertoire sizes. Males responded more strongly to tracks playing large song iii repertoires by singing faster in response and singing more songs. They also sang shorter songs that had lower frequencies and broader bandwidth. To evaluate inter-sexual selection pressures on repertoire size, I followed males throughout the breeding season to assess various proxies of female choice, including first egg lay date, clutch size, fledge count, and male prey delivery rate. None of the measures of female choice that I evaluated were related to her mate’s repertoire size. I conclude that song repertoires must be more important for assessing rival males in territory defense scenarios than for assessing potential mates in this species. These results support intrasexual competition as an important mechanism of selection that can lead to the elaboration of communication signals in bird species, and demonstrate that elaboration of song is not necessarily driven by mate choice dynamics. Intrasexually selected increases in repertoire size provide an alternative mechanism to female choice generating complexity for animal signaling systems. iv ACKNOWLEDGMENTS I thank first and foremost my advisor Dr. Lauryn Benedict for her guidance, advise, collaboration, and encouragement throughout this project. I am immensely grateful she has imparted on me how to be a better research biologist over the past two years, and her leadership inspires me in numerous ways as a young female scientist. I thank Dr. Mitchell McGlaughlin and Dr. Scott Franklin for their valuable contributions to my graduate education and their helpful feedback and advice on project design, data analysis, and writing this thesis. I would especially like to thank my lab colleagues Nadje Najar, TJ Hathcock, and Karina Sanchez for feedback on all aspects of the project’s progression and for dynamic lab discussions about birds and bird song. This research would not have been possible without the contributions of the Colorado Field Ornithologists, the Colorado Mountain Club, and the University of Northern Colorado’s Graduate School and School of Biological Sciences. I am grateful towards all the undergraduate students that helped watch birds and analyze camera trap data. I am sincerely thankful to Nathanial Warning for loaning me a set of Reconyx Field Cameras for observing Rock Wrens at nests. I have the most gratitude to my husband, Robin Pitt, for all his love and encouragement to help me through this graduate program, and to my parents, Melanie and Philippe Gobert, for their never-ending support and for teaching me the value of perseverance and hard work. v TABLE OF CONTENTS CHAPTER I. BACK GROUND AND LITERATURE REVIEW …...……………………………… 1 Song Type Repertoires as Targets of Sexual Selection Rock Wren Natural History Research Goals II. TESTING THE TERRITORY DEFENSE FUNCTION OF SONG TYPE REPERTOIRE SIZE IN ROCK WRENS USING PLAYBACK EXPERIMENTS …...………………… 31 Introduction Methods Results Discussion III. USING BEHAVIORAL OBSERVATION TO ASSESS ROCK WREN SONG TYPE REPERTOIRE SIZE IN RELATION TO MALE QUALITY AND PARENTAL INVESTMENT …...…………….….…….……….… 62 Introduction Methods Results Discussion IV. SUMMARY AND FUTURE DIRECTIONS…...…………………………….……… 86 Implications for the Function of Song Repertoire Size Rock Wren Population Declines Natural History Notes REFERENCES …...…………………………………………………………....….….……… 92 vi APPENDICES A. TABLE OF NEST OUTCOMES FOR ALL DISCOVERED ROCK WREN NESTS INCLUDING NEST CHECKING DETAILS BY DATE ….….……….…….….……….…….….……….…….….……….…….….… 102 B. PREY DELIVERY ITEMS AND NEST VISITS IN THE FIRST FIVE DAYS POST HATCHING BY MALES, FEMALES, AND AN UNKNOWN PARENT INCLUDING PROPORTIONS CONTRIBUTED BY EACH PARENT ….….……….…….….….….….……….… 105 C. PLAYBACK EXPERIMENT LOCATIONS BY FIELD SITE AND ROCK WREN HOME RANGE SIZE IN HECTARES ….….……….….….……… 114 D. INSTITUTIONAL ANIMAL CARE AND USE COMMITTEE APPROVAL …….….……….…….….……….…….….……….……..……..…..… 116 vii LIST OF TABLES TABLE 1. Linear mixed model results for time to first flight approach ….….……….….……… 48 2. Linear mixed model results for closest approach distance to speaker ….…..….….… 49 3. Linear mixed model results for time to first singing ….….……….…….….………… 50 4. Linear mixed model results for the number of songs sung between track repetitions ….….………..……………..….….….…...….……….…….….……….… 51 5. Mean number of songs sung between playback track repetitions by playback track repertoire type ….….………………………….….………..…….….……….… 51 6. Mean song measurements in 5-minute periods pre- and post- first playback repetition and results of a generalized linear mixed model ….….….….….….…….... 52 7. Mean song measurements in 5-minute periods post- first playback repetition by playback repertoire type and results of a generalized linear mixed model ….……………………………………..…..…..…..........…..………...…......…. 53 8. Linear mixed model results of song type diversity use ........……...…….……..….….. 55 9. Reproductive measures of nesting pairs confirmed to have a nest ………………...… 75 10. Linear regression correlation results of song type repertoire size in relation to multiple measures of mated male quality and female preference …….………....… 76 11. Prey types delivered to all nests combined and proportion of the total by type of prey ..…….….…………….…………..…..….…..….….…….….….....…..…. 77 12. Number of prey deliveries by males and females at each nest ….….……….…….…. 78 13. Linear regression of amount of prey delivered by male in relation to home range size, fledgling success, and repertoire size ….….………..…....….…………… 79 viii A1. Table of nest outcomes for all discovered Rock Wren nests including nest checking details by date ..……..………….…………….………………….……...… 103 B1. Prey delivery items and nest visits in the first five days post nestling hatching for LB17 ..……...…...……...……....…….……..……….…………..…..… 104 B2. Prey delivery items and nest visits in the first five days post nestling hatching for So21 ……….……...….……....…….……..…….….…......................… 106 B3. Prey delivery items and nest visits in the first five days post nestling hatching for So28 ..……..……..…......….…....…….……..……….…..………….… 107 B4. Prey delivery items and nest visits in the first five days post nestling hatching for So30 .…..……...….……....…….……..…….……….…………..….…. 108 B5. Prey delivery items and nest visits in the first five days post nestling hatching for So34 ..……..………..…...…….......……..……..…..….…………….… 109 B6. Prey delivery items and nest visits in the first five days post nestling hatching for So36