Thirty meters long. Up to 200 tons in weight. The biggest creature ever to live abounds on Sri Lanka’s porches. The elusive blue whale, twice the weight of the hugest known dinosaur, seems to like Lanka as much as anyone would.
This past decade has established Sri Lanka as one of the world’s premier locales for seeing and studying blues. Beneath shallow waters outward from Lankan shores lies continental shelf: a gently sloping sea floor stretching to an edge where the bottom drops steeply into the deep. Blues enjoy cruising deepening waters at shelf edges.
They find lots to eat there and they may use the shelf edges in navigating. The southernmost wedge of the Indian (sub)continental shelf happens to ‘pinch in’ close to the Lankan shore at Mirissa in the south, precisely where blues migrating back and forth between the Arabian Sea and the Bay of Bengal find their shortest route.
Blues feed almost exclusively on krill, thumbnail-size crustaceans which swarm in huge orange clouds. Krill feed on microscopic plants (phytoplankton) or on microscopic animals (zooplankton) grazing on those phytoplankton.
The richest krill blooms arise in chilly northern and southern waters where phytoplankton and zooplankton thrive best because cold seas hold more nutrients needed for phytoplankton photosynthesis than tropical seas do. Sri Lanka sits in tropical seas of course, so if blues are finding krill here, something quite unusual might be happening.
One explanation could be a tropically-rare abundance of nutrients in Lankan waters, due to its steep topography and monsoon rainfall. Some one hundred rivers and streams flush from Sri Lanka’s land surface into its surrounding ocean. Nutrients gush downward and outward into the nearby seas. Teensy plants synthesize the organic slurry with sunlight so that krill can eat their fill and blues dine in style.
Why is blue so huge? Earth’s largest animal must necessarily be aquatic and must eat low on the food chain. The heaviest animals need to be aquatic because water provides buoyancy helping hold up weight. The largest terrestrial dinosaur was roughly the same length as blue whales but only half their weight.
Animals as heavy as blues would collapse as land-dwellers or be too sluggish to move. The demand on legs to hold up and move land animals constrains their maximum weight. At sea, water’s buoyant force presses upward to counteract gravity, keeping aquatic creatures from simply falling to the bottom of the sea. No legs required.
The next point is that on land the largest plant-eaters are invariably bigger than the largest carnivores. This was true in the age of dinosaurs—veggie Dreadnoughtus shrani outweighed meat-shredding Spinosaurus eightfold–and it remains true today: elephants are way heftier than grizzly bears.
Why don’t carnivores ever reach the size of the largest herbivores? Top predators face constraints on size that herbivores avoid in accord with what’s called the Second Law of Thermodynamics as it operates in food chains (what eats what).
Sunlight furnishes essentially all energy available to life on earth for biomass construction and metabolism. Plants convert solar energy into plant stuff, which herbivores eat and convert into herbivore stuff.
Primary carnivores convert herbivore stuff into carnivore stuff and top predators do likewise with both large herbivores and lower-level carnivores. Food chains are therefore sequences of converting energy to mass, mass to energy again, energy again back to mass and so on.
The Second Law tells us that with each such conversion or transformation, much of the input energy will be lost or dissipated into what could be considered non-usable waste (actually heat). This means that at successively higher food chain levels (‘trophic levels’ biologists call them) the total energy available to support biomass and metabolism progressively dwindles.
Estimates hold that only 10% of the energy biologically embodied at any trophic level makes it through to get embodied at the next level upward. This means that the total energy available to species at the top of a typical food chain may be only 1/10,000th of that for herbivores grazing on plants at the base of the chain.
This in turn means that top predator species operate within far tighter energy budgets than herbivores do. Their constricted energy budget effectively limits carnivore size. If they grew larger, they would have to shrink their population numbers to stay within their available energy budget.
With shrinking numbers, finding mates for reproducing becomes increasingly difficult. The blue whale is a carnivore, to be sure, but not a top predator in the sense of hunting and eating large animals.
Blues are grazers–honorary herbivores–rather than hunters like typical large carnivores. They are only two steps up the food chain, as opposed to five or so for top predators. Fueled by massive ingestions of krill, blue whale energy budgets can sustain gigantic size without undue curtailment in population numbers or activity levels.
A typical blue feeding dive is a marvel. Strokes from powerful flukes power her downward against her own buoyancy through the first 25 meters. As she descends, pressure from the water above forces her flexible rib cage inward, decreasing her volume and increasing her density so that her buoyancy dissipates and she begins to fall rapidly with gravity toward the sea bed. She turns and heaves herself upward in a strenuous ‘lunge’ through krill blooms, fighting not only gravity but also the huge hydrodynamic drag created by her own gaping jaws.
After a few seconds, she shudders to a halt, having gulped maybe sixty tons of seawater into her ventral pouch. With a gelatinous tongue the weight of an elephant, she spews the water out through her baleen—cartilegenous venetian-blind-like sieves that line her mouth instead of teeth—retaining thousands upon thousands of krill then to swallow.
She does this all again and then again in a handful of successive lunges back toward the surface, holding her breath all the while of course. Her enormous krill binges furnish massive energy but also require huge energy outlays. Some marine biologists suggest that increasing blue size would actually decrease her energy yield per kilogram of body weight from lunging. Pushing the extra weight around would not yield enough extra krill to match the extra energy expenditure.
This means that blue is not only the largest animal ever to live on our beautiful planet but probably the largest that ever could. OK, but how smart is she? Certain items suggest she may not be at the top of her class among cetaceans.
A stepdown in smarts may go with the same factor that enables blue’s huge size: her grazing lifestyle. High-IQ cetaceans like orcas (killer whales), sperm whales and bottlenose dolphins all live by the hunt.
Bottlenoses and orcas collaborate amongst themselves in intricate prey-snatching tactics, while sperm whales team up for either joint or sequential hunting dives and also maintain complex networks of reciprocity in cooperative calf care and raising, requiring feats of memory and social maneuver.
Unlike these highly convivial hunters, blues do not seem to spend much time socializing in clusters. Many studies of animal intelligence emphasize congregation, communication and cooperation: bottlenoses, orcas and sperm whales all rank high on these metrics. Social learning appears to thrive where life circumstances fluctuate just enough so that conveyance of knowledge and experience is useful.
Oceanic predation seems to fit this bill nicely. Blues, by contrast, appear far less social, with simple mother-and-calf duos as their most common social formation. Lunge feeding through balls of krill does not at first glance seem to require much cooperation or brainpower. All these considerations suggest that blues may be a bit IQ-challenged, at least compared with the brainiest whales and dolphins.
Lest we be too hasty in attributing low wattage to blues’ brains, however, recall that elephants exhibit remarkable intelligence, despite their grazing lifestyle. Several items suggest that blues may not be as dumb as they look, even among cetaceans. First, blue brains are large, very large indeed.
A dominant school of thought is that species intelligence correlates mainly with brain-to-body size ratio (BBR). Humans have a higher BBR than any other animal except one: voila, we are super smart! Blues pack big brains to be sure, but with immense body size their BBR drops down, with their smarts perhaps dwindling in turn.
Another school of thought, however, is that intelligence corresponds also with absolute brain size, not just BBR. A tiny shrew exceeds humans in BBR but no one is nominating her for valedictorian. Sheer brain size means more neurons, more pathways, more flexibility, more capacity.
From this viewpoint, blues stand to rank high in intelligence, with the second biggest brain on the planet, exceeded only by sperm whales. And there may be more social learning in lunge feeding than there seems to be. First, there is being in the right place at the right time for krill blooms.
Blooms arise now and then, here and there, due to complex fluctuations in water temperature, nutrient supply, ocean topography, waves, currents, tides, competitive predation and so on. Blues need to know this stuff and they can learn it only from other blues: complex social transmission of knowledge may be needed.
Social learning may also apply to avoiding orcas, the only predators blues normally need to worry about. Moreover, because lunge feeding tends to scatter krill balls temporarily, blues at a krill ball site may need to coordinate so that all may feed: either lunge in unison or lunge sequentially so that feeding chances get shared.
Such complex social consideration and coordination could both require and reward sophisticated intelligence. Then there is this. Blues emit extremely loud moans so low in frequency as to be largely inaudible to the unaided human ear. These songs probably come only from males and likely play a role in locating or attracting mates. It appears plausible that blues hear each other calling for hundreds if not thousands of miles, perhaps across entire ocean basins.
This means they could be ‘in touch’ with one another far more intensively than would seem to be the case from the fact that they do not seem to ‘cluster’ that much. Blues subsist in eleven relatively distinct population groups spread across the world’s oceans. Each has a singing style common to all members but slightly different from that of other populations.
Recordings reveal the startling fact that the sound pitch of blue songs across all populations has dropped just a bit every year for the past thirty years, as long as we have been listening. Populations must be following one another’s songs so that they all move in the same direction: slightly lower year by year.
Biologists understand ‘sexual selection’ as a process whereby females mysteriously and almost arbitrarily find certain male displays sexy. Masters of such display mate more successfully and pass genes producing those displays (e.g., peacock feathers) on to their sons, who themselves mate successfully in turn.
But the blue whale pitch shift cannot be an example of genetically-propagated sexual selection. It affects entire populations—indeed the entire species—year by year: far too fast to be genetic and generational. So we have males all changing their song display in uniform ways to keep up with what females for some reason deem sexy. I’m not sure whether this counts as a sign of high intelligence but I think I know what to call it: fashion.
(From the archives of Echelon magazine; published in September 2016)