«The Relationship Between Dominance and Vocal Communication in the Male Ring-Tailed Lemur (Lemur catta) by Laura McLachlan Bolt A thesis submitted in ...»
The Relationship Between Dominance and Vocal
Communication in the Male Ring-Tailed Lemur (Lemur catta)
Laura McLachlan Bolt
A thesis submitted in conformity with the requirements
for the degree of Doctor of Philosophy
Department of Anthropology
University of Toronto
© Copyright by Laura McLachlan Bolt, 2013
The Relationship Between Dominance and Vocal Communication in the
Male Ring-Tailed Lemur (Lemur catta)
Laura McLachlan Bolt
Doctor of Philosophy
Department of Anthropology University of Toronto Abstract Sex-specific calls are used in male-male agonistic encounters and male-female courtship in many animal species. The ring-tailed lemur (Lemur catta) is a gregarious Malagasy strepsirhine with twenty-two distinct vocalizations for adults, including two male-specific vocalizations and an additional vocalization with male-specific functions: the howl, the squeal, and the purr. Proposed intra-sexual agonistic functions for these three vocalizations have never been empirically tested.
This study’s purpose was to investigate the functions of howling, squealing, and purring in the ring-tailed lemur, and to assess the relationships between the rates of these vocalizations and male dominance. From March to July 2010, I collected 600 hours of total data and 480 hours of focal data on male ring-tailed lemurs aged three and older at Beza Mahafaly Special Reserve, Madagascar. I observed each male continuously for 30 minutes at a time and noted behaviours including all vocalizations and all agonism using one–zero sampling at 2.5-min intervals. I calculated male dominance rank and vocalization rates from these data. My results indicated that male dominance rank is correlated with male purring rate and with squealing rate, but not with howling rate. Male purring rate increased during intra-sexual agonism and was associated with aggression in agonistic encounters. Squealing rate increased during male-male agonism and indicated both aggression and submission in male-male encounters. Howling rate increased ii during inter-group encounters and a greater number of males participated in multi-male howling choruses when non-group members were present. Purring and squealing are agonistic vocalizations and used in male-male agonism in the ring-tailed lemur, while howling is used in inter-group encounters.
iii Acknowledgments I am grateful to many people and organizations for their help with this project. Firstly, I thank my supervisory committee for their contributions. I am very grateful to my academic supervisors, Shawn Lehman and Joyce Parga. I am aware of how much support and help they each provided me with throughout this process, and I thank them sincerely for the numerous ways in which they contributed to my dissertation. Due to their helpful feedback and great suggestions for improvement on each of my chapters, I completed a stronger doctoral project. I thank Esteban Parra, Michael Schillaci, and Dan Sellen for their feedback on my written dissertation and thoughtful questions during my defence. I am grateful to Drew Rendall for serving as my external examiner, and for his various helpful suggestions. I also thank the faculty and staff in the University of Toronto anthropology department for all of their help throughout my PhD program, particularly Natalia Krencil and Jack Sidnell.
I am appreciative of all of my fellow graduate students and other colleagues from University of Toronto’s anthropology department. Your help and feedback about my project has been invaluable, while your friendship and comraderie has contributed immeasurably to my graduate student experience. In particular, I thank Iulia Bădescu, Katherine Bannar-Martin, Ryan Burke, Brooke Crowley, Cadell Last, Keriann McGoogan, Catherine Merritt, Mike Reid, Abigail Ross, Travis Steffens, Erica Tennenhouse, Kim Valenta, and Amber Walker-Bolton. The scintillating conversations and copious e-mails of the anthropology “Meet ‘N Eat” group have kept me well-entertained over the years, and I thank Rastko Cvekic, Daniella Jofre, Dean Langan, Eugenia Tsao and all the others most sincerely for their food, fun, and friendship.
Beyond the University of Toronto, I am grateful to many influential teachers from all stages of my education. I thank them all, and in particular acknowledge Sinikka Valila Chantler, Muriel Kent, Brenda Ravenscroft, Nancy Stormes, and Mary Lousie and David A. White.
I was fortunate to have the opportunity to undertake field research in Madagascar for this dissertation. For their great support and facilitation of my project in Madagascar, I thank Andry Randrianandrasana and Jacky Ibrahim Antho Youssouf at the Beza Mahafaly Special Reserve.
My appreciation goes to Jeannin Rainavanosy and Joel Ratsirarson of the Département des Eaux et Forêts de l’Ecole Supérieure des Sciences Agronomiques (ESSA) and Madagascar National iv Parks (MNP) for permission to work at Beza Mahafaly, and to Madagascar Institut pour la Conservation des Ecosystèmes Tropicaux (MICET) staff, including director Benjamin Andriamihaja for their help with logistics. I thank Elahavelo, Efitiria, Enafa, Edouard, Ralaevo, and Monja of the Beza Mahafaly Ecological Monitoring team for field assistance, and Lala, Delaprairie, Voola, Etala, Efmoeza, Veloke and the rest of the reserve staff for their aid and kindness during my stay. Teague O’Mara and his assistants Ayden Sherritt and Cathriona Hickey provided invaluable help with my orientation at Beza Mahafaly. I am also grateful to Stephanie Meredith for her advice about what to expect at Beza. Finally, Michelle Sauther and Frank Cuozzo kindly provided me with ring-tailed lemur age data and have encouraged my work at Beza Mahafaly, for which I’m extremely grateful.
I had the opportunity to complete pilot research for this project on St. Catherines Island, USA. I thank the late president Frank Larkin, the Larkin and Smith families, and the SCI foundation board for allowing researchers to study both native and non-native wildlife on SCI. I am very grateful to the St. Catherines Island Foundation for their permission to conduct this research, as well as for providing me with housing and transportation while on the island. The Wildlife Conservation Society staff of the Wildlife Survival Centre on SCI aided my research, and I am grateful to WCF staff members and Timothy Keith-Lucas for their help. I also thank the SCI staff, especially superintendant Royce Hayes. They were all instrumental in facilitating my project. Finally, I thank Anna McFaul for providing me with field assistance while on SCI.
Shannon Digweed and Drew Rendall provided me with invaluable field experience early in my PhD, and I thank them for allowing me to assist in their red squirrel project. They introduced me to acoustic research and gave me practical experience in using the field techniques common to animal behaviour study, for which I am very grateful.
This dissertation was funded by an Alexander Graham Bell Canada Graduate Scholarship (CGS-D) from the Natural Sciences and Engineering Research Council of Canada (NSERC), Ontario Graduate Scholarships (OGS), the American Museum of Natural History, the Edward J.
Noble Foundation, the St. Catherines Island Foundation, and various awards, fellowships, and research grants from the University of Toronto. I thank all of these funding bodies for their generous support.
v My success would not have been possible without the support and encouragement of my friends and family. C.S. Lewis says, “friendship is unnecessary, like philosophy, like art…It has no survival value; rather it is one of those things which give value to survival.” I am grateful to the many good friends who have helped me in practical ways throughout this dissertation. Salina Morrow and Anya and Bob Willis provided me with housing when I first arrived in Toronto.
When my 2009 field season in Madagascar was postponed due to political unrest, Susitna Banerjee generously provided me with a place to live. Several others, including Kirsten and Kevin Martin, have offered me their basements in case I need a place to live in the future. Other friends have kindly provided me with transportation, including Amy and James Allingham, Julie Johnson and Mark Chown, Paula Morritt, and Anya Willis. Ryan Janzen aided me tremendously by advising me about many technical aspects of my project and helping with logistical issues while I was at remote field sites. Others sent encouraging notes and care packages to me at my field sites, including Amy Allingham, Ryan Janzen, Ruth Kiang, and Tristan Rhys Williams.
Friends including Ian Begg, Nick Collins, Ryan Janzen, Chloe Valenti, and Tristan Rhys Williams have all provided me with valuable academic and professional advice. Finally, I am privileged to have great friends near and far who have helped me to live a rich and varied life beyond academia. For their friendship and support through the years, I thank Amy and James Allingham, Susitna Banerjee and Debu Sen, Sarah Berry, Scott Brubacher, Laura Grace Conlon, Michael Chan and Maria Jose Sandi, Michelle Chan, Natalie Cheung, Nick Collins, Lelia Fry, Lisa and Mario Greco, Suzanne Grossman, Heather Hummel, Ryan Janzen, Julie Johnson and Mark Chown, Ruth and Paul Kiang, Tiffany Krahn and TJ Wry, Vincent Lai, Grayden Laing, Moray McGill, Kirsten and Kevin Martin, Paula Morritt, Salina Morrow and Kyu Shim, Angie and Jamie Nelson, Tina Roberts and Nicolas Bossile, Colleen Savage, Rachel Schmucker, Adelle Spouge, Chloe Valenti, Rebecca Walker, Marjorie and Ron Walker, Tristan Rhys Williams, Angela and Emyr Williams, Huw and Felicity Williams, Anya and Bob Willis, Jon and Nicole Wise, and anyone I have neglected to mention.
Ryan Janzen has tirelessly supported me through this dissertation, from its conception to the finished product, while his unflappable optimism has encouraged me throughout the process.
He has aided me in ways too numerous and varied to list. I am deeply appreciative of his input, and thank him profusely. I am fortunate to have him in my life.
vi Finally, I am deeply grateful to my family. My grandparents and great-grandparents were always very supportive of my academic endeavours, and would have been very proud to see me complete a doctorate. I think of Mary Olive Cunningham, Jack Wallace Cunningham, Lucille Mabel Bolt, Douglas Kitchener Bolt, Gordon Cecil Barber, Barbara Sherwood Barber, and Nellie Astles. I also thank my extended family for their support, and especially acknowledge my brother Jonathan Bolt, who has always been proud of my academic accomplishments, and my parents, Brian and Mary-Ellen Bolt. My parents have been unflagging supporters through all stages of my education, and I owe much of my success to their fortitude. They were a huge source of encouragement through my PhD program, and I am deeply appreciative of their myriad contributions. I am fortunate to have grown up in a household where education was valued and encouraged, and to live at a time and in a place with no limits imposed on my academic achievement. I think of my brave and hard-working ancestors, who lacked the educational opportunities available to my generation. From this long line of ancestors, my parents were each the first of their forebears to graduate from university, while I am the first to earn a PhD.
This dissertation is dedicated to my parents, Brian Douglas Bolt and Mary-Ellen Bolt.
Figure 2: Mean male ring-tailed lemur purring rate per hour during periods of male-male agonism versus male purring rate during times without agonism 46
Figure 5: Correlation between male ring-tailed lemur dominance index score and mean rate for purrs given during male-male agonism, with linear regression 49
Figure 4: Correlation between male ring-tailed lemur dominance index score and mean number of howls in a howling bout, with polynomial regression 85 Figure 5: Male howling rate per hour during periods when non-group ring-tailed lemurs were present versus male howling rate when no non-group members were present 86
Figure 3: Correlation between male ring-tailed lemur dominance index score and mean rate for squeals given during male-male agonism, with linear regression 118 Figure 4: Mean male ring-tailed lemur squealing rate per hour during periods of malemale agonism versus male squealing rate during times without agonism 119
Appendix II: Individual ring-tailed lemur howling rates and standard deviations 129 Appendix III: Individual ring-tailed lemur squealing rates and standard deviations 130
Sexual selection and male vocalizations In group-living animals, social relationships are mediated by a variety of signals (Bradbury and Vehrencamp, 1998). While many signals are used by both sexes, vocal signals related to mate attraction, copulation, and competition are often male-specific and have functions related to sexual selection (Andersson, 1994; Darwin, 1871). Sexual selection is a form of natural selection which operates between individuals of the same sex as they compete against one another for access to copulatory partners, and between members of the opposite sex as individuals make themselves attractive to potential mates (Darwin, 1871). According to the predictions of sexual selection theory, male vocalizations are thought to display individual strength, health, genetic quality, and suitability as an inseminator to females, while females are thought to choose males based on the quality and quantity of their vocalizations (Darwin, 1871;
Snowdon, 2004). Male vocalizations also display these qualities to other males, and show that the caller could win in a fight if challenged (Darwin, 1871). In this way, intra- and inter-sexual selection act on male vocalizations (Snowdon, 2004).