Socioecology, acoustic communication and demography of Asian elephants in Sri Lanka

251 Pages·2014·3.26 MB·English

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Publicly Accessible Penn Dissertations
Summer 2010
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Shermin de Silva
University of Pennsylvania, [email protected]
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de Silva, Shermin, "Socioecology, Acoustic Communication and Demography of Asian Elephants in Sri
Lanka" (2010). Publicly Accessible Penn Dissertations. 213.
https://repository.upenn.edu/edissertations/213
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SOCIOECOLOGY, ACOUSTIC COMMUNICATION AND DEMOGRAPHY OF ASIAN ELEPHANTS IN SRI
LANKA
Shermin de Silva (Author)
Dorothy L. Cheney (Supervisor)
Comparison of behavior across species brings to light the underlying social and ecological factors that
have shaped social organization and communication. Elephantids, the only living members of the
Proboscidean clade are cognitively sophisticated, long-lived, putatively social mammals. I examine how
vocal communication and social organization in Asian elephants (Elephas maximus) compare to African
savannah elephants (Loxodonta africana), as well as basic demographic and conservation issues
concerning Asian elephants.
The first chapter defines fourteen distinct acoustic signals based on their acoustic features, and
describes the contexts in which they occur. Most vocalizations are employed in contexts of movement,
and some vocalizations are used primarily during movement or non-aggressive social interactions. This
suggests that elephants actively seek out association with particular individuals.
The second chapter tests the hypothesis that associations among adult female Asian elephants are
governed by resourced availability, and describes the temporal structure and strength of bonds. This
study population demonstrates fission-fusion social dynamics in which individuals change companions
over short time scales, influenced by rainfall, but maintain stable relationships over long time scales.
In the third chapter I test the hypothesis that associations are purely the consequence of the spatial
distribution of resources, rather than social preference, using a modeling approach based on the spatio-
temporal coordinates of individuals. In all seasons, individuals appear to move in a coordinated manner,
supporting the interpretation that observed associations reflect true social preference. At the same time,
resource distributions do influence the size of social units, and their movements.
In the fourth chapter I review the most recent demographic studies of elephant populations in Asia as well
as Africa, and highlight the lack of data for much of Asia. I outline methods based on individual
identification that may be used to address this challenge to conservation and management. I apply these
methods to offer demographic estimates for the study site, and examine what constitutes good practice,
in the fifth chapter.
DDeeggrreeee TTyyppee
Dissertation
DDeeggrreeee NNaammee
Doctor of Philosophy (PhD)
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Biology
FFiirrsstt AAddvviissoorr
Dorothy L. Cheney
SSeeccoonndd AAddvviissoorr
Robert M. Seyfarth
KKeeyywwoorrddss
Asian elephant, Elephas maximus, vocal communication, social organization, demography, movement
SSuubbjjeecctt CCaatteeggoorriieess
Behavior and Ethology | Ecology and Evolutionary Biology | Life Sciences | Population Biology
This dissertation is available at ScholarlyCommons: https://repository.upenn.edu/edissertations/213
SOCIOECOLOGY, ACOUSTIC COMMUNICATION AND DEMOGRAPHY OF
ASIAN ELEPHANTS IN SRI LANKA
Shermin de Silva
A DISSERTATION
In
Biology
Presented to the Faculties of the University of Pennsylvania
In
Partial Fulfillment of the Requirements for the
Degree of Doctor of Philosophy
2010

Supervisor of Dissertation Co-Supervisor
Signature________________ Signature________________

Dorothy L. Cheney Robert M. Seyfarth

Professor of Biology Professor of Psychology

Graduate Group Chairperson
Signature___________________

Paul D. Sniegowski, Associate Professor of Biology

Dissertation Committee
David J. White, Assistant Professor, Psychology
Marc F. Schmidt, Associate Professor, Biology
Arthur Dunham, Professor, Biology
Socioecology, acoustic communication and demography of Asian elephants in Sri Lanka
2010
Shermin de Silva
This work is licensed under the Creative Commons Attribution-NonCommercial-
ShareAlike 3.0 License. To view a copy of this license, visit
http://creativecommons.org/licenses/by-nc-sa/3.0/
To my parents, Ananda and Dane de Silva, whose decision to pursue a new life twenty
years ago has made possible all opportunities for me, and who continue to lend me their
unwavering support.

iii
ACKNOWLEDGEMENTS

I thank Dorothy Cheney and Robert Seyfarth for enthusiastically taking on a
student going in a direction of research distinct from their own, having faith that I could
fulfill what I had set out to do despite striking out into uncharted territory, permitting me
to follow my own interests freely, and encouraging me when necessary. I will be forever
indebted to them for the many doors this has opened for me.
Devaka Weerakoon, Charles Santiapillai, and M.R. Mohammed helped to set up
the field site, clearing numerous obstacles that arose along the way. I am extremely
grateful to the Department of Wildlife Conservation, Sri Lanka, for enabling this
research, particularly the Director General Brig. W.A.D.A. Wijesooriya, Mr. S.R.B.
Dissanayake, and the Research Committee.
I thank David White, Peter Petraitis and Mark Liberman for their insights on
analysis, and Marc Schmidt, and Arthur Dunham for their encouragement throughout the
process. Christopher Cieri, Kevin Walker, Sarah Johnstone Drucker, and Ankit Jain
provided valuable technical assistance. Colleen Gasiorowski and Laurel Sweeney
shepherded me safely through these years; I was so reassured to know I was in good
hands. Equally, Kelly McGinnis and Greg Milewski made sure I dotted my i’s and
crossed my t’s when navigating the tricky waters of grants. Finally, undergraduates Anne
Sharpe and Ariel Stein dedicated much effort to cataloguing and counting elephants.
This work would not have been possible without the dedication of Ashoka
Ranjeewa, for whom the decision to join me has been a life-altering gamble. My success
is equally his, our joint investment in the future founded on an unshakable trust. In
iv
addition we relied heavily on his brother Kapila, our dear cook Anula Jorthipala, friend
and assistant Sameera Weeratunga, constant and reliable tracker Saman, the back-up
vehicles willingly provided by Grizzly Safari, and the good will of the other Uda Walawe
National Park personnel and wardens.
The past six years were enlivened by the people whom I will forever associate
with this stage of life - Anna Nesterova for blazing trails ahead, then showing me the
way; Peter Descioli, Maria Rakhovskaya, Kinjal Doshi, Grace Freed-Brown, and Ewa
Szymanska for sharing many adventures and making Philadelphia feel like home;
Nivedita Srinivas who has remained a true friend, our distance apart notwithstanding.
I cannot express how much I owe to my dearest aunt Nisha Suhood, who has
variously sacrificed time and money to help me during the times I needed her most. She
is the rock that has firmly anchored our work.
It has been my great fortune to meet and work with Sergey Kryazhimskiy. May
this be the beginning of a long and beautiful collaboration. He has steered me gently in
times of doubt, with encouragement that never fails to lift my spirits and aspirations.
This work was carried out in compliance with requirements of the Institutional
Animal Care and Use Committee of the University of Pennsylvania. It was partially
supported by an Integrative Graduate Education and Research Traineeship grant from
National Science Foundation (NSF-IGERT 0504487), a grant from the U.S. Fish and
Wildlife Asian Elephant Conservation Fund (grant no. 98210-7-G167), a grant from the
University of Pennsylvania Department of Biology Binns-Williams Fund, and a student
research grant from the Animal Behavior Society.
Lastly I thank the unnamable and unseen, which shapes all that is or will be.
v
ABSTRACT

SOCIOECOLOGY, ACOUSTIC COMMUNICATION AND DEMOGRAPHY OF
ASIAN ELEPHANTS IN SRI LANKA
Shermin de Silva

Dorothy L. Cheney

Comparison of behavior across species brings to light the underlying social and
ecological factors that have shaped social organization and communication. Elephantids,
the only living members of the Proboscidean clade are cognitively sophisticated, long-
lived, putatively social mammals. I examine how vocal communication and social
organization in Asian elephants (Elephas maximus) compare to African savannah
elephants (Loxodonta africana), as well as basic demographic and conservation issues
concerning Asian elephants.
The first chapter defines fourteen distinct acoustic signals based on their acoustic
features, and describes the contexts in which they occur. Most vocalizations are
employed in contexts of movement, and some vocalizations are used primarily during
movement or non-aggressive social interactions. This suggests that elephants actively
seek out association with particular individuals.
The second chapter tests the hypothesis that associations among adult female
Asian elephants are governed by resourced availability, and describes the temporal
vi
structure and strength of bonds. This study population demonstrates fission-fusion social
dynamics in which individuals change companions over short time scales, influenced by
rainfall, but maintain stable relationships over long time scales.
In the third chapter I test the hypothesis that associations are purely the
consequence of the spatial distribution of resources, rather than social preference, using a
modeling approach based on the spatio-temporal coordinates of individuals. In all
seasons, individuals appear to move in a coordinated manner, supporting the
interpretation that observed associations reflect true social preference. At the same time,
resource distributions do influence the size of social units, and their movements.
In the fourth chapter I review the most recent demographic studies of elephant
populations in Asia as well as Africa, and highlight the lack of data for much of Asia. I
outline methods based on individual identification that may be used to address this
challenge to conservation and management. I apply these methods to offer demographic
estimates for the study site, and examine what constitutes good practice, in the fifth
chapter.

vii