Why I don’t bite everyone that stresses me out: The cost-benefit analysis of predators

There is controversy whenever a human creates a close interaction with a wild animal.  Those arguing in favour of the human’s behavior inevitably settle on the argument that if the animal didn’t like it, the animal would have bit them or exhibited some sudden reaction to the human.  People who propose this argument have a very limited understanding of animal behavior.

Real talk, I used to believe this totally incorrect argument, and I will never forget the day that changed my perspective forever.  I was a budding zoologist working on a remote island with a group of scientists that were ringing cormorants.  The cormorants squawked for awhile, but then got “used” to our presence and calmed down.  I was reassured that we weren’t causing them any distress as we worked nearby, otherwise I expected that they would have shown it by either continuing to squawk or simply fly away.  Then, I noticed a few dead cormorants near where we worked.  I thought that they must have died before we arrived.  However, the senior researcher explained that they had been alive moments before but most likely died due to the stress of our presence.  That was an extremely powerful lesson in my young career and it challenged what I thought I “understood” about human interactions with animals.  Keep in mind, I was known for being an animal whisperer of sorts in my youth (see below) and truly believed that my special calm and confident nature could be detected by animals, and that they would accept my presence more readily than those who didn’t have my nature.  That FernGully perspective is wrong and egocentric.  There are few scenarios where our presence isn’t horribly stressful and disruptive to wild animals.   

Squirrel demonstrating a cost/benefit analysis = the benefit of free food is higher than the stress my tie-dyed presence is causing.

Large predators are no exception.  They are just as vulnerable to our stress as cormorants and just as unlikely to express it externally, because the cost of those behaviors is expensive.  Predators have severe energetic constraints and are constantly calculating whether their actions are worth sacrificing energy for, this is a cost/benefit analysis.  We do similar analyses all the time.  For example, I have a Trader Joe’s that is ~30 minutes from my home.  The food there is delicious and less expensive than my local grocery store.  However, I don’t go to The Joe every time I am hungry.  Even though I would save money on discount blue cheese dip there, I would spend more money in fuel for my car – meaning the entire trip would cost me more in the long run.  The costs of this behavior is too high and not worth it.

White sharks are especially discerning since they can burn a lot of energy quickly and are unlikely to encounter large meals in the open ocean to refuel.  So they make conservative decisions that prioritize maintaining energy stores (especially during gestation when a large portion of their energy budget is developing shark embryos).  In the recent case of large white sharks scavenging from a sperm whale in Hawaii, there were several divers in the water creating close interactions with the sharks for social media purposes.  Controversy ensued and the idea that the white sharks must have “enjoyed” these interactions otherwise they would have swam away or bit the divers has been presented.  But it is not supported.  First, white sharks full of whale blubber are experiencing some pretty hardcore torpor.  Also, blubber is very positivity buoyant, meaning a stomach full of blubber is essentially the same as if we ate a ton of foam and then tried to swim about.  White sharks at whale carcasses are typically slow-moving with low aggression, even towards each other.  It’s not that whale blubber makes them “happy,” it’s that being aggressive and swimming fast when there are going to be many other white sharks around AND you’re going to have a stomach full of floaty blubber is energetically expensive and the costs of these behaviors are too high.

Figure 4 from Fallows, C., Gallagher, A. J., & Hammerschlag, N. (2013). White sharks (Carcharodon carcharias) scavenging on whales and its potential role in further shaping the ecology of an apex predator. PLoS One8(4), e60797.

Does that mean diving with full-bellied white sharks is safe?  Absolutely not – for them or for you.  It doesn’t matter how well you think you “know” a predator – species or individual – they are still dangerous.  We all know the list of fatal tragedies that start off with well-known humans believing that they have enough experience to take big risks, and each of those fatalities ends with the animal suffering, too.  For the sharks, disrupting a rare feeding event has long-term implications.  The stress caused – whether they exhibit that stress externally or not – is burning their limited energy, forcing them to recalculate their future behaviours until (if?) they encounter the next windfall.  Also – although currently undocumented – it’s a common thought amongst shark researchers that mating could occur at large feeding events like whale carcasses since it’s provides male sharks an opportunity to take advantage of the large female’s torpor to attempt mating approaches (I personally believe the same is true at seal colonies).  Boats and divers disrupt these behaviours.

I don’t bite every person that causes me stress.  I don’t full-sprint away from every situation that causes me stress.  That doesn’t mean that I am not experiencing stress that impacts my behavior and health.  The same is true for every one of these close animal interactions created by humans.  It’s alarming to me when those humans say that they are somehow especially qualified, and that their experience alone creates these “safe” encounters.  It’s not.  You’re benefiting from the cost a large predator doesn’t want to incur by demonstrating its stress to you – but as we’ve unfortunately seen several times, when the scales are finally tipped, unnecessary tragedies do occur.