People seem to have a fascination with dolphins – they often interact positively with humans, & they show a wide range of complex & adaptable behaviour patterns. A new paper (Finn et al. 2009) describes complex prey handling in a wild bottlenose dolphin (Tursiops aduncus) off the South Australian coast. Given that it’s fairly hard to observe dolphins feeding in the wild, this observation adds to our understanding of the adaptability of dolphin behaviour.
Despite the difficulty of watching dolphins in the wild, scientists have still been able to describe quite a range of feeding behaviours. These include: using their ‘beak’ (the rostrum) to dig into soft sediments, using sponges as tools to protect their beaks when probing in sand or mud, using the tail to strike at fish or slap the surface to startle prey hiding in weed beds, working in groups to herd fish (including generating waves of water to wash fish up onto the shore, after which the dolphins deliberately beach themselves to grab their prey) (Finn et al. 2009),
The research team observed a female bottlenose dolphin repeatedly killing cuttlefish & preparing them to eat, using the same sequence of events each time. She drove the cephalopods over a sandy-bottomed area of the reef & then killed the selected prey animal by thrusting it downward against the seabed. Next she lifted it up & beat it with her beak, continuing this until the ink sac was empty – thus improving the quality of her eventual meal. The final step was to remove the ‘cuttlebone’ (that bit people feed their budgies) by rubbing the dead cuttlefish along the seabed until the skin over the cuttlebone was removed. (No crunchy bits!) It’s likely that fit, healthy cuttlefish could avoid the dolphin, but this hunting behaviour was centred on weakened, post-spawning individuals – thousands of cuttlefish come to spawn along the reef where this hunting behaviour was observed.
What’s more, it’s possible that more than just one dolphin in a pod uses this technique: ‘boat-based observers have… [often] witnessed clean intact cuttlebones floating to the surface… [near] pods of foraging dophins’ (Finn et al. 2009), and other divers have witnessed the same behaviour sequence.
This opens up the potential for the cuttlefish-killing sequence to be learned – a possible example of cultural transmission of foraging behaviour.
J.Finn, T. Tregenza & M. Norman (2009) Preparing the perfect cuttlefish meal: complex prey handling by dolphins. PLoS ONE 4(11): e4217