Communication Studies on the Bottlenose Dolphins around Mikura Island, Japan

Work on the Mikura bottlenose dolphins (Tursiops aduncus) offers a unique opportunity to examine dolphin behavior in a setting far different from the Bahamas. The clear water and habituation to humans by dolphins around Mikura Island offer predictable opportunities for observing the social behavior and structure of dolphins from underwater, similar to the setting in the Bahamas. Dudzinski's research in Japan has a primary focus, with a secondary comparative aspect. The focus concerns dolphin signal exchange and use of contact behaviors between individuals. Dudzinski is interested in the social behavior and communication of dolphins. Related comparative questions focus on the similarities and differences in use and production of contact and vocal behavior as well as signal exchange among individuals between the Mikura Island bottlenose dolphins and the Bahamas' Atlantic spotted dolphins. Do individuals from both groups exhibit similar group types? Do they exhibit similar behavioral activities in their given habitats? Do individuals within both study populations use vocalizations differently? Do they interact with conspecifics similarly given similar group types or behavioral activities? Could the difference in habitat for the two locations - far from shore, white sand in the Bahamas versus near-shore, boulder-covered sea floor around Mikura - play a significant factor in any observed differences in behavioral activity or signal exchange? Study Animals: Bottlenose Dolphins (bandoiruka) Observations on bottlenose dolphins around Mikura Island have been ongoing since the early 1980's. Systematic collection of data in the form of video and photographic recordings have been conducted since 1994 (T. Iwatani, I.C.E.R.C. Japan, pers. comm., 1996). Work by ICERC and the Mikura Bottlenose Dolphin Kenkyukai volunteers estimate the current population size frequenting the waters within 300 m of Mikura shores at about 165 individuals. A 1:1 sex ratio of identified dolphins has been reported, although this ratio does not hold within different age classes. There are many more young males than females and more adult females as compared with adult males. Early analyses suggest that adult females with calves are the most frequent group types observed around Mikura Island.

Justin Gregg joined Dudzinski and DCP in 2005 to continue studying the dolphins around Mikura Island for his doctorate. His work relates to echoic eavesdropping and joint attention behaviors among dolphins. Both Gregg and Dudzinski collaborate with Japanese researchers who also study the dolphins around Mikura Island. Together, we continue to expand our knowledge and database on these amazing creatures.

Objectives

1. To conduct focal animal and all-occurrence observations to determine how the shallow, near-shore inlets around Mikura Island are used by bottlenose dolphins.
2. To identify vocalizing individuals and examine variation in whistle production and use according to individual, age, gender and activity.
3. To document production and use of pulsed vocalizations by individual dolphins.
4. To record with video and still photography the exchange of signals including contact and vocal behaviors among individual dolphins.
5. To identify similarities and differences in signal exchange and interactions between Mikura bottlenose and Bahamas' Atlantic spotted dolphins.

Methods of Data Collection
Focal animal and focal group follows provide the framework for data collection focusing on dolphin signal exchange and contact behavior. Simultaneous video & audio recording of identified dolphins and real-time, all-occurrence documentation of specific behaviors and group activity provide a data record. A mobile video/acoustic system (MVA) is used to record dolphin behavior and sound.

Definitions (additional compared to Bahamas study)
->   Group - The "total available dolphins" observed within an imaginary ellipse, with a 200 m long axis & 100 m short axis for dimensions. The long axis placed parallel to the Mikura coastline.
->   Subgroup - Dolphins observed in apparent association, moving in the same general direction, although not all individuals necessarily heading in the same direction, and engaged in the same activity. Spatially, each individual in a single subgroup is within at least five dolphin-body widths of its nearest conspecific.
->   Short Encounter - Any underwater observations of dolphins between 30 s & 180 s. Underwater observations of dolphins that are greater than 180 s become true encounters by definition.

Preliminary Results

Through DCP, Dudzinski spent 29 days on Mikura Island and had 15 boat trips to gather data observing dolphins interact and communicate. We spent 30 hours and 20 minutes looking for dolphins (i.e., effort) and recorded 3 hrs, 2 min. of video. With our preliminary analyses, we have identified: 8 Adult females, 3 Adult males, 6 sub-adult females, 10 sub-adult males, 4 juvenile females and 2 juvenile male dolphins. We saw 4 mother/calf pairs for which the calf was a year old. Merging our preliminary records with those of the Mikura Iruka Kyoukai for this season, we saw 88 different individual bottlenose dolphins: this represents a 61.54% re-sighting rate just for May and June this year, with respect to the study population size documented in 2000.

We were lucky to gather several hours of data with our new echolocation click detector (ECD) boards. Because these boards allow us to capture all information associated with dolphin echolocation clicks (~120kHz) that are not audible to our ears, we need to rely on computers to download the data. Preliminary checks of the audio tapes confirmed that we did indeed record at least something from the dolphins when they approached the camera, scanned with their heads and made sounds. With computers we have confirmed the frequency (kHz) that the dolphins were using when investigating the camera, Dudzinski, and the other swimmers. Analyses of the tapes are ongoing, and we should be able to post details by the end of 2001.

For those of you interested in some background information about Dudzinski's research on the dolphins around Mikura Island, you can download her report covering her research from 1997 to 1999.

JSPS Final Report - September 1999

Mikura Summary Report - 2002

Extended Information

Work on the Mikura bottlenose dolphins (Tursiops truncatus) offers a unique opportunity to examine dolphin behavior in a setting far different from the Bahamas. Mikura Island is a dormant volcanic island with a boulder coastline. Depths range from four to 20 meters within 150 m of shore, dropping sharply to more than 100 m depth at about 200 m from shore. Dolphins can be seen in the surf zone near Mikura Island as well as in the deeper waters. In the Bahamas, Atlantic spotted dolphins are regularly observed between 40 and 60 km from shore in shallow (< 8 m) water with a white sandy bottom. The clear water and habituation to humans by dolphins in both locations offer predictable opportunities for observing dolphin social behavior and communication underwater.

Details of intra-specific interactions and signal exchange as related to dolphin age, gender and associates were examined for spotted dolphins (see Bahamas page for details & references). But it was not possible to determine if the observed exchanges were simply related to dolphin characteristics, or if external factors played a significant role in specific associations. Information gathered on the Mikura bottlenose dolphins will facilitate a comparison of vocal and behavioral activities with those of spotted dolphins as related to varying social associations and habitat differences (open, flat, sandy bottom vs. coastal, rocky sea floor).

PROTOCOL FOR BEHAVIORAL DATA COLLECTION (OBSERVATIONS AND RECORDINGS) ON BAHAMAS’ ATLANTIC SPOTTED DOLPHINS AND BOTTLENOSE DOLPHINS AROUND MIKURA ISLAND, JAPAN).

My research in Japan has a primary focus, with a secondary comparative aspect. The focus concerns dolphin signal exchange and use of contact behaviors between individuals. I am interested in dolphin social behavior and communication. The comparative aspect is between my work on Atlantic spotted dolphins and that on the bottlenose dolphins around Mikura Island. My questions are detailed below in the form of objectives and hypotheses.

Objectives

To conduct focal animal and all-occurrence observations to determine how bottlenose dolphins use the shallow, near-shore inlets around Mikura Island.

To identify behavior and vocal exchanges between interacting individuals.

To identify dolphin group activity from underwater and surface observations.

To identify vocalizing individuals and examine variation in whistle production and use according to individual, age, sex and activity.

To document production and use of pulsed (i.e., click) sounds by individual dolphins.

To determine if low frequency clicks, captured with the mobile video/acoustic system, contain an echolocation frequency or represent a distinct frequency (kHz).

To characterize other pulsed sounds (e.g., squawks, whines) and determine if they contain a high frequency signal similar to echolocation clicks.

To record signal exchange including contact behavior and sounds between individual dolphins.

To identify how these signals are related to dolphin identification, age, sex, group type and behavioral activity.

To identify signal senders and receivers during interactions.

To determine if correlations exist between sender/receiver roles and dolphin age, sex, associates, and activity.

To identify similarities and differences in signal exchange and interactions between Mikura bottlenose and Bahamas' Atlantic spotted dolphins

To identify any group type or composition differences.

To identify any differences in activity during encounters with dolphins.

To determine if observed variations in behavior, activity or signal exchange may be related to habitat differences (i.e., external factors).

Related comparative questions focus on the similarities and differences in use and production of contact behavior and sounds as well as signal exchange between individuals between the Mikura Island bottlenose dolphin and the Bahamas' Atlantic spotted dolphins groups. Do individuals from both groups exhibit similar group types? Do they exhibit similar behavioral activities in their given habitats? Do individuals within both study populations use sounds differently? Do they interact with conspecifics similarly given similar group types or behavioral activities? Could the difference in habitat for the two locations - far from shore, white sand in the Bahamas versus near-shore, boulder-covered sea floor around Mikura - play a significant factor in any observed differences in behavioral activity or signal exchange?

Data Collection

This protocol is for Japan & Bahamas except where noted.

Focal animal and focal group follows provide the framework for data collection focusing on dolphin signal exchange and contact behavior - communication. Two methods of collection will be followed for each swim encounter with dolphins: 1) simultaneous video and audio recording of identified dolphins; and 2) real-time, all-occurrence documentation of specific behaviors and group activity. Real-time, all-occurrence sampling will provide information on the overall behavioral activities of the dolphins. Information on the associations of vocal and tactile/visual signs of dolphins will be obtained primarily from video recordings, while corroborative evidence will be gathered in the form of anecdotal observations.

Focal individuals will be chosen opportunistically depending on individuals observed during swim encounters. The decision of which dolphin to watch is by chance with attention to an even representation of all age and both sexes. A focal session will start as soon as the observer is in position underwater and the group composition is assessed. Video recording will continue until the animal(s) leaves the field of view. Thus, duration of focal follows is dictated by dolphin behavior: video observations on individuals will continue for as long as possible while in the field.

A mobile video/acoustic system (MVA) will be used to record dolphin behavior and sounds (Dudzinski et al., 1995). The system is swimmer-propelled and facilitates localization of dolphin sound sources by associating video data of animal distributions with audio data from two hydrophones spaced relative to the human inter-aural distance as scaled to speed of sound in water. A small second housing containing a Sony TCD D8 digital recorder together with a pre-processor circuit which detects the highly directional part of a dolphin's echolocation 'clicks' and makes these audible and recordable will also be used.

Definitions