Featured Image Credit:Sue Flood/NPL
By Eva Gruber
Humpback whales have been in the news recently for their pretty consistent altruistic behaviors – seeming to selflessly putting themselves in between predators and their prey, in a supposed effort to save the preys’ lives. Since this isn’t a common occurrence in the tooth-and-claw reality that is the natural world, scientists have been seeking an evolutionary explanation for this behavior.
Altruism seems to be the behavior that divides the heartfelt from the jaded. There is a divide between people who see animals sacrifice their own comfort, and sometimes even their own lives, for the benefit of other animals, and the people who see it as merely a calculated way to earn something in return. Science has had a hard time studying altruism as not only is it pretty rare in the non-human animal kingdom, but it is also highly complicated behavior with a suite of variables that prevent experimental control.
Most altruism that has been studied has taken place between animals who are directly related – i.e. they share the same genes. The explanation for this has been rather simple – self-sacrifice is little sacrifice at all if the animal who is benefitting shares a lot of genes with you. After all, this falls right in line with the “selfish gene” theory.
But some animals, such as humpback whales, exhibit the rarest of all altruism – not only with animals who are not related to them, but animals who aren’t even the same species! In particular, these gentle giants seem to hold a grudge against some of the top predators of the sea – orca whales.
There have been several documented instances of humpback whales thwarting orcas’ attempts to capture their prey. From humpbacks in the Antarctic fending orcas off from a seal stranded on a floe of ice, to the San Juan Islands of Washington State, where orcas can’t get a decent meal of sea lion if there are humpbacks in the area.
What might be going on here? The answer is still somewhat of a mystery. But it is reminiscent of the “mobbing” behavior seen in birds, where small songbirds will “mob” (continuously follow, harass, and attack) larger birds such as crows and hawks – which might pose a threat to them or their eggs or young. In the case of humpback whales, they might be “mobbing” the orcas when they sense aggressive behavior. When the orcas engage in predatory attacks, the humpbacks move into action not necessarily to protect the prey animal, but to encourage the aggressive orcas to leave the area, since orcas do pose a threat to baby whales.
In fact, while orcas have been seen often preying on gray whale calves, only in 2014 was it confirmed that orcas do in fact also prey on humpback whale calves. An orca pod tracked for six days, attacked humpback whale calves eight times, and successfully killed three calves. So, the threat for humpback whales is very real, and this explains their animosity for orca whales – and why they might always be willing to bully their cetacean cousins out of the area.