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| Photo of a humpback whale, taken by Dr. Louis Herman for the NOAA [i] |
Humpback whales (Megaptera novaeangliae) have been observed taking the ‘kill’ out of killer whales (Orcinus orca) by fighting back when targeted, as well as interfering with their hunts on all kinds of mammals, even when the humpback itself was not in any danger. An article by Robert L. Pitman and colleagues [1] reviewed old accounts of interactions between the two species in an attempt to unearth the reason for interfering, and the results of the analysis were astonishing!
It was found that almost all interactions were between the subspecies of killer whales that exclusively hunt mammals [2] (as opposed to the fish eating subspecies). Within these interactions, the researchers noticed that killer whales almost entirely went after humpback calves, other species of mammals, and rarely juvenile humpbacks; never adults. This was mainly thought to be because full grown humpbacks are fully capable of defending themselves, and as such not viewed as viable prey by the orcas. Because of this, it’s clear to see that when humpbacks interrupt orcas, it’s not purely out of self-preservation; after all, full grown adults have nothing to fear.
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| A pair of mammal eating (transient) killer whales breaching taken by Robert Pitman for the NOAA. [ii] |
When orcas do approach humpbacks or seals and other smaller mammals, humpbacks have been observed to quickly swim to the scene, pursuing and disrupting the killer whales for as long as 7 hours! The signal that appeared to play the most obvious role in summoning the humped heroes was the orcas’ own attack calls! This is supported in part by the fact that humpbacks don’t just aid other humpbacks, as well as by the fact that whales have been shown to be agitated by killer whale vocalizations [3]. Whether approached or picking the fight themselves, humpbacks displayed the same form of aggression: slapping their flukes and slashing with their highly maneuverable [4], massive [5], and armor covered (barnacle encrusted) [6] flippers. Adult humpback whales pose a serious threat to orcas, causing the monochromatic mammals to keep their distance once the display has begun for fear of injury!
The cost of interrupting normal activities to fight orca on mammal crime is non-trivial; after all, most interactions took more than 1 hour on average. Especially considering that humpbacks saved all mammals, including various species of seals and pinnipeds, and that the majority of observed interruptions were for non-humpbacked species, this extreme response seems unnecessary. However, when considering how long mothers care for their calves and the investment a calf represents, it’s understandable that the chance to protect humpback calves is worth the massive amount of false positives. Or perhaps humpback whales are simply the Batman of the sea, duty bound to keep it’s underwater denizens safe, no matter the cost.
References:
[1] Pitman, R. L., Deecke, V. B., Gabriele, C. M., Srinivasan, M., Black, N., Denkinger, J., Durban, J. W., Mathews, E. A., Matkin, D. R., Neilson, J. L., Schulman-Janiger, A., Shearwater, D., Stap, P. and Ternullo, R. (2016), Humpback whales interfering when mammal-eating killer whales attack other species: Mobbing behavior and interspecific altruism? Marine Mammal Science. doi:10.1111/mms.12343
[2] Jefferson, T. A., P. J. Staceyand R. W. Baird. 1991. A review of killer whale interactions with other marine mammals: Predation to co-existence. Mammal Review 21:151–180. (Journal article online)
[3] Curé, C., L. D. Sivle, F. Visser, et al. 2015. Predator sound playbacks reveal strong avoidance responses in a fight strategist baleen whale. Marine Ecology Progress Series 526:267–282. (Journal article online)
[4] Edel, R. K., and H. E. Winn. 1978. Observations on underwater locomotion and flipper movement of the humpback whale Megaptera novaeangliae. Marine Biology 48:279–287. (Journal article online)
[5] Tomilin, A. G. 1967. Mammals of the USSR and adjacent countries, Volume 9. Cetacea. Translated by Israel Program for Scientific Translation, V. G. Heptner, ed., Jerusalem, Israel.
[6] Ford, J. K. B., and R. R. Reeves. 2008. Fight or flight: Antipredator strategies in baleen whales. Mammal Review 38:50–86. (Journal article online)
Media Credits:
[ii] Photo by Robert Pitman: http://www.afsc.noaa.gov/Quarterly/amj2005/divrptsNMML3.htm
I think the evolutionary forces driving this altruistic behavior would be interesting to study in more depth, especially with regards to the humpbacks that aid other species. One thing that gets confusing with more complex mammals is how to define their cognitive processes. Many human behaviors are culturally formed instead of evolutionarily driven, and when we start talking about really high-order animals such as whales, it's plausible that the reason they engage in certain behaviors isn't necessarily selection for the behavior itself but for the "personality trait" that drives it and might be evolutionarily advantageous in another context.
ReplyDeleteGood point! But I think the idea of selection for a personality trait that drives many different linked behaviors, not all of which are advantageous, applies for all kinds of animals -- not just the ones we think of as socially and cognitively "complex".
DeleteGood point! But I think the idea of selection for a personality trait that drives many different linked behaviors, not all of which are advantageous, applies for all kinds of animals -- not just the ones we think of as socially and cognitively "complex".
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