Learning what not to fear
A University of St Andrews biologist has revealed a new insight into the way harbour seals protect themselves from one of their main predators.
Published in today’s edition of Nature (14 November 2002), the study, by Volker Deecke, showed that harbour seals are capable of recognising the acoustics of harmless fish-eating killer whales, therefore, saving time and energy to protect themselves from their main threat – mammal-eating killer whales.
The study was undertaken in conjunction with the University’s Professor Peter Slater and Dr John Ford of the Pacific Biological Station, Canadian Department of Fisheries and Oceans.
Funded by the Vancouver Aquarium Marine Science Centre where he is a research associate, Volker claims that, because the calls of fish-eating killer whales are extremely variable, this discrimination illustrates a “rare and formidable learning task”. The study also documents complex learning in wild animals while most previous studies were undertaken in captive settings and its significance shows how wild animals focus on real threats in their environment through learning and experience.
Volker, who conducted the fieldwork in Canada, focused on the underwater calls of two distinct forms of killer whale – “resident” whales which live in large groups and which feed exclusively on fish, and “transient” whales which live in smaller groups and prey only on marine mammals. The two forms do not interbreed, rarely interact and show striking differences in their vocal behaviour.
The study involved Volker conducting two playback experiments off southern British Columbia, Canada. An underwater speaker was dropped into the sea from a small boat anchored around 100 metres from a seal haulout. In the first experiment, the researcher played playback sequences containing calls of mammal-eating killer whales and control sequences containing no calls to find out if seals responded to killer whale calls. They found that seals escaped by diving when hearing the calls, but not when control sequences were played.
The second experiment involved playing three types of sequences consisting of calls of local fish- eating killer whales from British Columbia, unfamiliar fish-eating killer whales from Alaska, and mammal-eating killer whales respectively. The seals responded very strongly to the calls of mammal-eating killer whales, as well as to those of harmless but unfamiliar fish-eating killer whales from Alaska. However, they showed hardly any response to the calls of the familiar fish-eating killer whales from British Columbia. This shows that seals are able to discriminate between the calls of different forms of killer whales. The results also show that seals consider all unfamiliar killer whale calls as dangerous, but have learned that the calls of the local fish-eating population do not signal danger.
Volker believes that, by discriminating between the acoustics of two populations, the seals are saving valuable time and energy and, ultimately, staying alive.
Volker said, “Responding to calls in a general and indiscriminate manner is a huge energy cost. An over-general response causes an animal to respond to harmless cues and therefore waste time and energy. Rather than learning the calls of dangerous killer whales, our results suggest that seals initially respond to all calls but habituate to those that are never followed by an attack. By “learning what not to fear”, seals are able to focus their fear on the real threat in a way that does not require experience with the predator.”
Part of the Bird and Mammal Sound Communication Group within the School of Biology, Volker will be starting a post-doctoral fellowship at the University of British Columbia in January 2003, studying the vocal behaviour of killer whales in Alaska with a focus on interactions between killer whales and Steller sea lions.
NOTE TO EDITORS
For further information, please contact Volker Deecke in Vancouver from 9am until 5pm Pacific Standard Time (GMT -8hrs) – telephone +1.604.659.3429, fax +1.604.659.3599 or email vd2@st- andrews.ac.uk.
High-resolution jpeg photographs of harbour seals and transient killer whales available from Gayle Cook – 01334 467227 or 07900 050 103.
Broadcast media are welcome to download recordings of the sounds used in the experiments – available at http://biology.st- andrews.ac.uk/sites/bmscg/nature.ht m. For higher quality recordings (16 bit WAV), please contact Volker direct.
Issued by Beattie Media on behalf of the University of St Andrews For more information please contact: Gayle Cook on 01334 462529, 07900 050 103 or email gec3@st- andews.ac.uk View University press releases on- line at http://www.st-andrews.ac.uk Ref: volker/standrews/chg/13nov002