Not so friendly dolphins

The image of the dolphin as a peaceful mammal looks more like a myth than a reality:

Harbour porpoises are being killed in increasing numbers by bottlenose dolphins around British coasts, possibly due to competition for food.

The evidence comes from counts of porpoises washed up on coasts and from post-mortem examination of the animals.

A lack of fish may be turning the dolphins on their cetacean relatives, according to some scientists.

And it isn't just the work of some rogue individuals:

Acting on their own, or with others, bottlenose dolphins ram the porpoises with their beaks, causing multiple injuries that include internal bleeding, rib fractures, ruptured lungs dislocated spines.

No one seems to know why the dolphins are so violent:

One theory suggested the violence may be re-directed aggression when access to females is limited. But female dolphins have also been observed taking part in the attacks on porpoises.

Another idea is that the behaviour might help to develop hunting skills, even though the victims are never eaten.

This is evidence that any animal - even the supposedly peaceful dolphin - will become violent if it is in its best interests to do so.