Above & Beyond Whales: Are High-Frequency Food Calls Successful?

Humpback whales (Megaptera novaeangliae) in the eastern Pacific migrate annually to their feeding grounds in the Gulf of Alaska. Some engage in a cooperative foraging behavior called bubble-net feeding whereby a small group of whales work together to capture fish. Some group members dive below a school of herring and blow a curtain of bubbles to trap the fish, while other group members produce long sequences of loud, low frequency vocalizations known as ‘food’ calls (Hanser, 2009). Food calls are signals, and therefore shaped by natural selection for effective transmission, and for their effectiveness in altering the receiver’s behavior to the sender’s benefit (Wiley and Richards, 1978). Playback experiments (Sharpe, 2001) have shown that fish respond to food calls by moving closer together and crowding toward the surface, making food capture easier for the whales. Food calls may also be used by the whales to coordinate this group behavior (Hanser, 2009). Humpback whales typically produce food calls at a frequency of about 500 Hertz (Hz) (Cerchio & Dahlheim, 2001). While analyzing recordings of whales performing bubble-net feeding using the software program Audacity, we observed that some food calls were produced between 800 and 1000 Hz (what we’re calling high frequency food calls). While it’s not clear why these high frequency calls were produced, we wanted to know if their use had any effect on the success of the feeding event in which they occurred. Because signals are specific to their function, we expected that series with high frequency food calls would result in fewer successful feeding events compared to traditional 500 Hz food calls. We tested this by comparing the success of high frequency call series with the success of randomly selected traditional call series of the same length.