Last updated 02/20/04 Other research links can be found at CBL Links.
Pacific Coast Bottlenose Dolphin Vocalizations and Behavior
Eric Howarth's is currently working on the relationship between dolphin vocalizations and behavior. Visual observations on the behavior of coastal bottlenose dolphins are often obscured by the turbidity of coastal water conditions, the substantial amount of time these dolphins spend submerged, and by the darkness of nocturnal periods. In contrast, dolphin vocalizations may be monitored and recorded under a wide range of water conditions, when dolphins are at the surface or submerged, and at night. If a relationship between dolphin vocalizations and behavior can be documented, then vocal activity may be used to provide access to important behavioral processes under a broader range of environmental and daytime conditions. Bottlenose dolphins make a variety of sounds by varying the structure of whistles and very short clicks. Both whistles and clicks have been associated in the literature with social behavior as well as with foraging and feeding activities (Tyack 1976, Norris et al. 1994, Dudzinski 1996). Historically, the CBL has assessed biologically important behavioral processes (states) through a synthesis of observed behavioral events such as steep dives, body contact, aerial displays and progressive movement (Weaver 1987, Hanson and Defran 1993). The documentation of “behavior states” using a sampling strategy consisting of two to three minute observations on focal groups is, thus, a well practiced research procedure in our lab (Barre 1994, Simonaitis 1991, Tepper 1996, Day 1998, Ward 1998)
Dolphin vocalizations will be detected by as many as four hydrophones which will be deployed in the nearshore coastline off of Torrey Pines State Park in North San Diego County. Past research has shown that this coastal area is frequently used by coastal bottlenose dolphins. Dolphin vocalizations will be detected by the hydrophones and transmitted by FM radio signal to a receiving station on top of a nearby cliff. This acoustical data collection system, which draws heavily on U.S. Naval submarine tracking technology, was developed during pilot research already completed. Behavioral displays associated with vocalizations will be simultaneously observed and recorded at the same cliff-top receiving station. Vocalization recordings will be categorized into clicks and whistles will be digitally analyzed on a time vs. frequency spectrogram. Both clicks and whistles will be cross-tabulated with behavior and associated environmental conditions.
The goal of this research will be to find significant trends in vocalization type and occurrence that may be associated with behavior states and environmental conditions. For example, behavior states such as feeding and socializing may be associated with a higher proportion of whistles and clicks compared to travel, rest or play. We currently have only a limited knowledge of the nocturnal behavior of Pacific coast bottlenose dolphins and data collected in this research may permit the analysis of nocturnal behavior by monitoring vocalizations.
Eric's thesis project used passive localization to determine the nocturnal movement and distribution of bottlenose dolphins at Torrey Pines State Beach. You may download a PDF version from abstracts section of his laboratory website - Association of Coastal Marine Ecologist.
References
Barre, L. M. 1994. Behavioral sequence analysis of bottlenose dolphins (Tursiops truncatus). Master's thesis, San Diego State University, California. 88 pp.
Day, J. 1998. Nocturnal movements and behavior patterns of Pacific coast bottlenose dolphins, (Tursiops truncatus). Master's thesis, San Diego State University, California. 128 pp.
Dudzinski, K. M. 1996. Communication and behavior in the Atlantic Spotted Dolphins (Stenella frontalis): relationships between vocal and behavioral activities. Ph.D. dissertation, Texas A&M University, Galveston, TX. 213 pp.
Hanson, M. T. and R. H. Defran. 1993. The behavior and feeding ecology of the Pacific coast bottlenose dolphin, (Tursiops truncatus). Aquatic Mammals 19:127-142.
Norris, K. S., B. Würsig, R. S. Wells & M. Würsig. 1994. The Hawaiian spinner dolphin. The University of California Press, Berkeley.
Simonaitis, M. K. 1991. Daily movement patterns and behavior of the Pacific coast bottlenose dolphin (Tursiops truncatus). Master’s thesis, San Diego State University, San Diego, CA. 79 pp.
Tepper, E. 1996. Feeding duration in the Pacific Coast bottlenose dolphin (Tursiops truncatus). Master's thesis, San Diego State University, California. 81pp.
Tyack, P. 1976. Patterns of vocalization in wild Tursiops truncatus. Senior honors thesis. Harvard University, Harvard, MA. 61 pp.
Ward, B. 1998. Movement patterns and feeding ecology of the Pacific Coast bottlenose dolphin (Tursiops truncatus). Master's thesis, San Diego State University, California. 102 pp.
Weaver, A. C. 1987. An ethogram of naturally occurring behavior of bottlenose dolphins, Tursiops truncatus, in southern California waters. Master's thesis, San Diego State University, California. 93 pp.
Last updated 02/20/04
Other research links can be found at CBL
Links.