Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2016
Description:
To maintain the benefits of group membership, social animals need mechanisms to stay
together and reunite if separated. This thesis explores the acoustic signals that dolphins
use to overcome this challenge and mediate their complex relationships in a dynamic 3D
environment. Bottlenose dolphins are the most extensively studied toothed whale, but
research on acoustic behavior has been limited by an inability to identify the vocalizing
individual or measure inter-animal distances in the wild. This thesis resolves these
problems by simultaneously deploying acoustic tags on closely-associated pairs of known
animals. These first reported deployments of acoustic tags on dolphins allowed me to
characterize temporal patterns of vocal behavior on an individual level, uncovering large
variation in vocal rates and inter-call waiting time between animals. Looking more
specifically at signature whistles, a type of call often linked to cohesion, I found that
when one animal produced its own signature whistle, its partner was more likely to
respond with its own whistle. To better evaluate potential cohesion functions for
signature whistles, I then modeled the probability of an animal producing a signature
whistle at different times during a temporary separation and reunion from its partner.
These data suggest that dolphins use signature whistles to signal a motivation to reunite
and to confirm identity prior to rejoining their partner. To examine how cohesion is
maintained during separations that do not include whistles, I then investigated whether
dolphins could keep track of their partners by passively listening to conspecific
echolocation clicks. Using a multi-pronged approach, I demonstrated that the passive
detection range of echolocation clicks overlaps with the typical separation ranges of
Sarasota mother-calf pairs and that the amount of time since an animal was last able to
detect a click from its partner helped explain its probability of producing a signature
whistle. Finally, this thesis developed a portable stereo camera system to study cohesion
in situations where tagging is not possible. Integrating a GPS receiver, an attitude sensor
and 3D stereo photogrammetry, the system rapidly positions multiple animals, grounding
behavioral observations in quantitative metrics and characterizing fine-scale changes that
might otherwise be missed.
Description:
This work was supported by the Office of Naval Research (N000140910528 and
N000141210417), the WHOI Marine Mammal Center, WHOI Biology Department,
WHOI Academic Programs Endowed Funds, the MIT Martin Family Foundation for
Sustainability, the MIT Graduate Student Government, the Grossman Family Foundation,
and the Danish Council for Independent Research (11-107628).
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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