Two humpbacks breaching for the heck of it
While there are a number of varied species of baleen whales that are adapted to their particular habitats and natural histories, there are a few things they have in common; they’re all much larger than we are, they all graze on small organisms, they all migrate over long distances, and they all communicate in the low frequency range. It is this last characteristic I want to excavate here.
Low frequency sounds propagate much further than higher frequencies in water and air for a few reasons. One is that the longer wavelengths of low frequency sound are not effectively absorbed or blocked by items smaller than half their wavelength. Another is that for a given amplitude, low frequencies contain a lot more energy per cycle. This gives us a psychoacoustic gauge on how large things are. Small things like bicycles and kittens make higher-frequency noises, large things like locomotives and whales make low-frequency noises.
This low-frequency, long-distance propagation characteristic is handy for the whales, as they can communicate across ocean basins with their deep voice. There is a lot of speculation about what they are using these long wavelength sounds for. Perhaps some form of live mapping? Maybe they are conveying information to their kin? Or low-frequency echolocation over long distances?
A new paper examines another possible communication channel that baleen whales may be using to announce their presence to each other – breaching! This is a dramatic behavior that is a delight to behold. If you’ve ever seen a beast the size of a school bus blast out of the water, you’ll know that the word “thrilling” pales.
Researchers found that humpback breaching and other surface behaviors like tail and fin slapping were more likely to occur when other humpbacks were greater than 4km from each other. This body-pounding and tail slapping would create a low-frequency underwater impulse. So by correlation that suggests that they may be using this to announce their location to each other over intermediate distances.
There is a common train of thought in biology to treat all activities in the context of an “energy economy;” that there must be some equal-value trade-off between expending energy and getting food, sex, or safety. This thinking is a bit tedious as it doesn’t account for emotional investments – such as altruism, play, or just plain exuberance!
Anthropomorphizing – or ascribing human sentiments and emotions to animals is one of the slow-fading taboos in the biological sciences. Stating that animals might be “happy” or “sad” somehow grates on biological rationalists. But on many occasions I’ve been on whale-watching boats where across the entire horizon where a humpback could choose anywhere to breach, but they decided to breach right by our boat – to the delighted squeals and cheers of a boat-load of eco-tourists.
I can’t speak for the humpbacks, but for me the phrase “tons of fun!” comes to mind.