Date of Award

Summer 2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Biology

First Advisor

Dorothy L. Cheney

Second Advisor

Robert M. Seyfarth

Abstract

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.

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