Local environment and population demographics, not genetics, influence bottlenose dolphin 'names'', a study concludes. By combining linguistic analysis with acoustic characteristics of individual call types, researchers have shown how local environmental conditions and population demographics influence bottlenose dolphin 'names'. Researchers were surprised by the findings. "There are so many different dolphin sounds, and we wanted to know if the animals were communicating with each other," explains study author Richard Connor from the National Marine Mammal Foundation (NMMF). "In some areas, bottlenose dolphins are giving two different calls in different situations. For example, one call is given for following ships and another when approaching boats." The team first determined the range of sounds produced by bottlenose dolphins. Then they set up a remote hydrophone in La Jolla, CA and recorded dolphin sounds at different times of day and during different behaviours. During daytime hours, males and females were calling frequently. In response to the presence of boats and other large vessels, the animals gave a distinctive type of call -- it is the one given during other activities but with a much faster and more repetitive pitch and sound volume. advertisement Using the recordings as a sort of sonic 'dictionary', Connor and colleagues searched the internet and dolphin catalogues and books for possible vocalisations that might be similar to those recorded in their study site. Using this method, they identified 21 potential call types and grouped these into eight groups. They then used computers to analyse the phonetic properties of these calls. The researchers were able to see that all the calls recorded at La Jolla were of the groups they expected to be unique to the area. For example, the group that contains sounds given during a greeting display is only seen in two other areas in the USA, but not at all in Hawaii. "In Hawaii, the animals greet with whistles, not dolphin 'names'," says Connor. "In this case, it's geography, not genetics." Connor and colleagues also analysed the acoustic properties of the calls. "For example, we thought that if animals were using their names to remember each other, then the same calls should occur repeatedly," says Connor. "But we found this was not the case." While there are some calls that seem to be used by all bottlenose dolphins, these are not in any pattern that would allow a dolphin to recognise other individuals. "Instead of using names, bottlenose dolphins may be using other dolphin sounds, like whistles, clicks, and high frequency squeals, to identify each other," explains Connor. "It might be that some calls have been copied because of their acoustic properties and become part of the dolphin repertoire. On the other hand, perhaps these signals have some biological significance. A little work is needed to determine if other animals are reacting to them, and if so, what they are doing." The bottlenose dolphin sounds described in the study have implications for the potential role of dolphins as sentinels of the environment. Bottlenose dolphins have been shown to modify their behaviour based on the level of noise pollution in the area, suggesting they are reacting to environmental sounds that are out of their control. But the findings of this study suggest the dolphins may be reacting to these environmental sounds instead of the noise itself. The dolphin sounds also have implications for whale researchers who record and analyse the 'names' of certain whales and use these sounds as evidence in studies of whale migration routes and whale populations. "The fact that the dolphins change their calls in different habitats means that whale researchers will need to be careful in how they use such recordings in their analyses," says Connor. "If the animal has a different call when it's away from the group, for example, then that might be missed in the analysis. You will get wrong data." The results of the study also challenge our idea that dolphins have to be genetically related to use the same calls. "We might think that all the dolphins in this study are related, but this could be a sampling error or even a biased one," says Connor. "What if there were two groups of bottlenose dolphins using these sounds in La Jolla -- one more closely related and the other less related?" While in general it's hard to determine if two or more animals are related, studies have found bottlenose dolphin social groups use the same sounds and whistles during social interactions. The dolphins can identify individuals and recognise themselves when listening to their own vocalisations, so it makes sense that they are calling each other in the same manner that they identify themselves. But more research needs to be done. "One area that has been challenging for the field has been determining what specific dolphin characteristics impact the way they produce a given vocalisation," Connor adds. "For example, acoustic differences might exist between animals in different geographic areas or with different lifestyles. I'm sure there are people out there who are experts in that." "As technology improves and acoustic listening becomes more prevalent, we hope to add to the database and continue to discover unique dolphin sounds," Connor says. "In my view, we need to understand how these calls are used. Are they for group identification? We want to know why they are calling and how they are using these sounds."