The second animal sound in our introduction is a recording of an elusive kind of killer whale. Did you know there was more than one kind?

I’m Lisa Strong for the Petersburg Marine Mammal Center.

By careful observation, scientists have identified two types of killer whales in our local waters: Residents and Transients. A team led by Volker Deeke, a researcher from University of British Columbia, spent two weeks last year in and around Frederick Sound tagging, tracking and listening to transient killer whales.

DEEKE: It’s a very interesting setup. We have two forms of killer whales living in the same waters, much like two human tribes that share common territory, but don’t interact much and the transients are mammal hunting killer whales so they go after things like seals, porpoises and sea lions. The residents are fish eating killer whales and their main prey is Pacific salmon.

Their dining choices influence their behavior. Residents tend to travel in large, vocal family groups, while transients are quiet, choosing to move in smaller groups. Why the difference?

DEEKE: Transients do not nearly vocalize as often as residents and that’s probably because they hunt prey that has very good underwater hearing. Seals, sea lions, porpoises…they can all hear killer whale calls from substantial distances and use them as a warning sign to get away. Residents, the fish-eating ones, they hunt salmon and salmon have lousy underwater hearing so there is no cost for those resident killer whales to vocalize and that’s why they do it much more often than the transients.

But as you heard in our recording, transients do vocalize. Deeke recorded this riveting sound after the transient group he was following made a successful kill. And he’s seen one of these silent groups breach and vocalize – completely blowing their cover, when they heard another transient group 15 miles away declare their successful kill. Transients may have a more complex social structure than their small group size suggests.