Each bottlenose dolphin produces her/his own signature whistle.
These whistles appear to communicate the identity, location, and also the emotional state of the dolphin making the whistle.
Vocal learning appears to help dolphins develop a novel whistle, and this happens early in life.
Signature whistles usually make up about half of the whistles of a wild dolphin, but they may increase to 100% of the whistles when a dolphin is isolated from other dolphins.
When isolated, a dolphin emits more signature whistles than any other whistle-type, which often helps researchers identify the signature of that dolphin
When dolphins are in a group, researchers have long had difficulty sorting out the whistles. Which are signature whistles and which are non-signature whistle-types?
New research, however, has developed a novel identification method, called SIGnature IDentification (SIGID). It can identify signature whistles among recordings of groups of dolphins.
It turns out that signature whistles tend to be repeated in groups, each within 1-10 seconds of each other, while non-signature whistles tend to occur in longer or shorter intervals between whistles.
Long-time SDRP collaborator Vincent Janik, from the University of St. Andrews, Scotland, and his colleagues used 47 hours of recordings of wild SDRP dolphins to develop and test the SIGID method. They then verified it with a sample of dolphins from the Duisburg Zoo in Germany.
Their article was published on-line in Marine Mammal Science, and is available from the publisher. SDRP Director Randy Wells is a co-author on the paper. The abstract is below.
The SIGID method has already been applied successfully on a project by Nicola Quick and Vincent Janik to identify signature whistles in Scottish bottlenose dolphins. Their efforts helped to document how dolphins exchange signature whistles when they meet each other at sea. This article was published on-line in the Proccedings of the Royal Society B, is available from the publishers.
Janik, VM , King, SL, Sayigh, LS & Wells, RS 2012, ‘ Identifying Signature Whistles from Recordings of Groups of Unrestrained Bottlenose Dolphins (Tursiops truncatus) ‘, Marine Mammal Science Article first published online: 19 MAR 2012. DOI: 10.1111/j.1748-7692.2011.00549.x
Bottlenose dolphins (Tursiops truncatus) have individually distinctive signature whistles. Each individual dolphin develops its own unique frequency modulation pattern and uses it to broadcast its identity. However, underwater sound localization is challenging, and researchers have had difficulties identifying signature whistles. The traditional method to identify them involved isolating individuals. In this context, the signature whistle is the most commonly produced whistle type of an animal. However, most studies on wild dolphins cannot isolate animals. We present a novel method, SIGnature IDentification (SIGID), that can identify signature whistles in recordings of groups of dolphins recorded via a single hydrophone. We found that signature whistles tend to be delivered in bouts with whistles of the same type occurring within 1–10 s of each other. Nonsignature whistles occur with longer or shorter inter-whistle intervals, and this distinction can be used to identify signature whistles in a recording. We tested this method on recordings from wild and captive bottlenose dolphins and show thresholds needed to identify signature whistles reliably. SIGID will facilitate the study of signature whistle use in the wild, signature whistle diversity between different populations, and potentially allow signature whistles to be used in mark-recapture studies.
Quick NJ & Janik VM. 2012. ‘Bottlenose Dolphins Exchange Signature Whistles when Meeting at Sea’, Proceedings of the Royal Society B. Article first published online: 29 FEB 2012. DOI: 10.1098/rspb.2011.2537