People love killer whales. Trained orcas in amusement parks draw millions of visitors; movies about captive killer whales yearning for freedom make millions at the box office.

But these large, black and white sea-going mammals are not universally loved by all species. In fact, they are downright loathed and feared by the animals they kill and eat, namely fish and seals. While fish have much accepted this sobering fact of marine life, harbor seals have learned to guard against being a killer whale's main course.

Killer whales communicate in a variety of dialects. There are discernible differences, however, between the chatter of killer whales that eat only fish and those that eat both fish and seals. According to one study, harbor seals can eavesdrop on killer whales to distinguish the harmless fish-only eaters from the seal killers.

In an experiment, scientists recorded both fish-eating and seal-eating killer whales and then played the sounds in the vicinity of a group of harbor seals. While the fish-eating whale calls caused only five percent of the seals to scatter, the seal-eating whale calls caused over forty percent of the seals to dive for safety.

To make sure that the seals were not simply afraid of all killer whales and had learned to ignore the fish-eating locals through observation, the researchers played tapes of seal-eating whale dialects that the test seals had never heard. Again, nearly forty percent of seals swam for cover. Scientists have hailed the findings as part of the growing evidence attesting to the complexity of predator-prey relationships.