Humpback whales interfering when mammal‐eating killer whales attack other species: Mobbing behavior and interspecific altruism?

• Published in: Marine Mammal Science
• Main Authors: Pitman, Robert L., Deecke, Volker B., Gabriele, Christine M., Srinivasan, Mridula, Black, Nancy, Denkinger, Judith, Durban, John W., Mathews, Elizabeth A., Matkin, Dena R., Neilson, Janet L., Schulman‐Janiger, Alisa, Shearwater, Debra, Stap, Peggy, Ternullo, Richard
• Other Authors: National Oceanic and Atmospheric Administration, National Geographic Society
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2016
• Subjects: Megaptera novaeangliae; Orca; Orcinus orca
• Online Access: http://dx.doi.org/10.1111/mms.12343; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fmms.12343; https://onlinelibrary.wiley.com/doi/pdf/10.1111/mms.12343

Abstract Humpback whales ( Megaptera novaeangliae ) are known to interfere with attacking killer whales ( Orcinus orca ). To investigate why, we reviewed accounts of 115 interactions between them. Humpbacks initiated the majority of interactions (57% vs . 43%; n = 72), although the killer whales were almost exclusively mammal‐eating forms ( MEKW s, 95%) vs . fish‐eaters (5%; n = 108). When MEKW s approached humpbacks ( n = 27), they attacked 85% of the time and targeted only calves. When humpbacks approached killer whales ( n = 41), 93% were MEKW s, and ≥87% of them were attacking or feeding on prey at the time. When humpbacks interacted with attacking MEKW s, 11% of the prey were humpbacks and 89% comprised 10 other species, including three cetaceans, six pinnipeds, and one teleost fish. Approaching humpbacks often harassed attacking MEKW s (≥55% of 56 interactions), regardless of the prey species, which we argue was mobbing behavior. Humpback mobbing sometimes allowed MEKW prey, including nonhumpbacks, to escape. We suggest that humpbacks initially responded to vocalizations of attacking MEKW s without knowing the prey species targeted. Although reciprocity or kin selection might explain communal defense of conspecific calves, there was no apparent benefit to humpbacks continuing to interfere when other species were being attacked. Interspecific altruism, even if unintentional, could not be ruled out.