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Biology of Marine Mammals (MSCI/BIOL.375)[ Course Homepage] [Syllabus] [Lecture Schedule] [Lab Schedule] [Student Presentations] [Marine Mammal Links] |
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Biology of Marine Mammals (MSCI/BIOL.375)[ Course Homepage] [Syllabus] [Lecture Schedule] [Lab Schedule] [Student Presentations] [Marine Mammal Links] |
Herzing, D.L. and C.M. Johnson. 1997. Interspecific Interactions Between Atlantic Spotted Dolphins (Stenella frontalis) and Bottlenose Dolphins (Tursiops truncatus) In The Bahamas, 1985-1995. Aquatic Mammals 23:85-99.
Purpose
This study examines the behavioral contexts in which interspecies interaction occurs, and the duration, group size, sex composition, and the ratio of these two during such encounters.
Study Site
South of Little Bahama Island
Methods
Results
- mixed species and sex groupings of spotted and bottlenose dolphins in different behavioral contexts
Discussion
Interspecies groups are larger than single species groups, and the combined mass of the mixed groups could be more effective at detecting, deterring or repelling predators.
The data on foraging relations between the two species was limited, in that mixed groups were least often observed.
Signal recognition has been observed between the two species mentioned in this study for acoustic signals and behavioral cues.
Shared aggressive behaviors, including open-mout6h threats, squawks, and head to head posturing, have been described for various dolphin species.
Among the unexpected findings reported was the occurrence of interspecies coalitions.
Similar behavioral types of interspecific interactions were observed across species.
Conclusion
In the Bahamas, bottlenose and spotted dolphins have been observed using both intra- and interspecific cooperation for both interspecific and inter-individual conflicts.
For social animals, like cetaceans, intragroup cooperation and competition may involve the fine art of sharing and co-opting signals and may include the necessity of establishing long term relationships and patterns of familiarity with conspecifics as well as interspecific neighbors.
Summaries:
It seems that the male bottle-nosed dolphins are in the habit of forming rather vicious gangs of three or more members. They work in concert to capture females of their species by chasing the smaller and weaker gals, thudding up against them, biting the damsels and then mating with them. In addition, the gangs often carry out their raids to capture the females of other male bottle-nosed-dolphin gangs, resulting in fights that can be pretty grim indeed -- and the gangs stay together for as long as 12 years.
Insight on the News, Sept 6, 1999 v15 i33 p4.
Title: Say It Ain't So: Flipper, Gang Leader? (Research into aggressive behavior of male bottlenose dolphins)
Author: Stephen Goode
This work suggests that a blurt of low-frequency sound described as a bray might be a hunting call. Researchers had once speculated that such an oddball noise might be a weapon. One old experiment determined the sound level needed to kill a guppy, but braying a fish to death turned out to be ridiculously hard. Scientist now say that the noise is more of a calling from one dolphin to round up other dolphins for foraging and group hunting, especially around schools of fish.
Source: Science News, May 27, 2000 v157 i22 p346.
Title: Dolphins bray when chasing down a fish. (Brief Article)
The association between white-fronted terns, Sterna striata, and Hector's dolphins, Cephalorhyncus hectori, during near-shore foraging of the latter is investigated. Significant association between terns and dolphins were observed during austral spring and early summer. Terns were observed to associate with 15.7% of surface-feeding dolphin groups. This is an example of facultative commensalisms that may be particularly useful during the terns' breeding season.
Source: The Condor, August 1998 v100 n3 p560(3).
Title: Feeding associations between white-fronted terns and
Hector's dolphins in New Zealand.
Author: Stefan Brager
Monkey Mia's dolphin society seems fluid. Individuals may shift from one group to another every few hours, or even minutes. Such transient groups may be of either sex, or both. But there is an underlying order. Adult males bond together in durable pairs or triplets. In most animal species, such groups would consist of relatives. With dolphins they seem to be just friends who have teamed up: blood brothers rather than the real thing. Numbers bring advantage against hostile neighbors, for example, and, not least, in the mating game. Groups of males will pursue reluctant females, often herding them into shallow water where their room for manoeuvre is limited. The inevitable follows. Rape, even gang rape, is not unknown among other wild animals. But dolphins have perfected the practice. The team doing the herding is often shadowed at some distance by another. if outsiders try to steal the first team's victim, the back-up group will come to the rescue-not of the female, but of their male friends.
The Economist (US), August 3, 1991 v320 n7718 p75(3)
Sisterhood is powerful. (researchers find cultural differences between dolphin societies)
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