Citation: Blanding, D. (2004) Patterns in whistling behavior as related to diurnal activity, gender and age in captive bottlenose dolphins (Tursiops truncatus) in Roatan, Honduras.
Darcie Blanding. Unpulbished Bachelor of Science Thesis, University of Rhode Island

Project Description:

The primary goal of my internship project was to determine what factors might influence whistling behaviors in dolphins including diurnal periodicity as well as age and sex. A difference between age classes in whistling behavior might suggest that dolphins must learn when and how to use whistles. I used data collected by the Dolphin Communication Project (DCP) at the Roatan Institute for Marine Sciences (RIMS), Anthony's Key Resort on Roatan, Honduras. RIMS has a collection of 17 captive bottlenose dolphins (Tursiops truncatus) that have been studied as one of DCP's non-invasive focal individual study of signal exchange. Whistles were recorded during rest, direct swimming, social interaction, aggression, foraging and more (see general definitions in Reynolds & Rommel, 1999, Mann et al., 2000). Whistles are frequency-moderated pure tones that can be produced with or without pulsed tones (e.g., clicks).

For this study, I defined whistles subjectively by aural discrimination: pure tones with a distinct silent space between them when produced consecutively. A whistle bout was a set of whistles by a single dolphin. I analyzed video data and conducted focal follows of individual and identified dolphins to determine which animals produced each whistle bout. Then, I classified these whistle data by dolphin age, sex and time of day. I used chi-squared, contingency tables and non-parametric statistics to analyze the frequency of each potential whistle pattern. I compared and contrasted these patterns based on gender, age and diurnal patterning.

Significant differences were seen in all aspects of the study with respect to age. The trends could be attributed to learning, social or signal complexity or group cohesion, depending on the age class. Something interesting to look at in future studies would be the correlation between age and sex and to compare adult males with adult females, etc. to develop an idea of rearing, learning or social behaviors and how they may differ between age/sex groups.

There was no significant difference in any of the analyses pertaining to sex. This result is similar to the studies of wild populations conducted by the Dolphin Communication Project in the Bahamas and around Mikura Island, Japan.

There are definite trends seen between the different time periods of the day, specifically noon was greater than both morning and afternoon periods for whistle production. This may be related to underwater visibility, activity levels, tides and currents, and training interactions.

There was a significant difference with regards to the individuals and age but not with sex. Causes for this variation may again pertain to visibility. That is, it is illogical and cost-expensive to exert energy to create bubbles when other dolphins would likely not be able to see them or respond to them as visual cues. A future study should examine what affect, if any, the addition or removal of individual dolphins could have had on the data - i.e., dolphin whistle production.

My study was limited by use of only aural documentation of dolphin whistling behavior. In future, whistles and whistle bouts should be digitized for a more accurate calculation of the duration of each whistle. Another topic that could be examined is whether or not boats had any influence on the number of whistles produced or if boat noise might have affected whistle duration. Again, the affects that the removal or addition of other dolphins may have caused in the whistling patterns of the dolphins in the group would be interesting to investigate. All of these factors will be included in my continued research for the Master's Degree program in Fisheries and Animal Science at the University of Rhode Island. For my MS degree, I will continue to work with Dr. Dudzinski and the Dolphin Communication Project, Mystic Aquarium & Institute for Exploration.