Killer whales living off the west coast of the US are extending the length of their calls to each other to be heard above the din of heavy boat traffic. The findings come from an analysis of killer whale, or orca, calls by British and US researchers which has been published in the journal Nature. The orcas make longer calls when boats are present in an apparent attempt to be heard above the engine noise. But the orcas only take this action when noise reaches a critical level. The killer whales observed in the study came from a population that lives close to the shore in waters off Washington state.