Why do humpbacks breach?
Breaching is performed by humpbacks of both sexes (unlike the song, which is just the males) and all ages. It’s not clear why they do it, but the frequency, style and function may differ with season and location.
Breaching costs a lot of energy, and calves appear to do it the most. Since their mothers provide very rich milk (45–60 per cent fat) for at least 10 months, perhaps nursing youngsters don’t need to worry about wasting energy. Breaching could thus be a form of play that helps them to develop skills to use in later life.
Among adults, breaching is far more common in social species, such as humpbacks, that gather at their breeding grounds. This suggests that it plays a role in communication. For example, North Pacific humpbacks breach most in their southern mating areas and less frequently in their northern feeding areas.
Regardless of where the behaviour occurs, it is often associated with whales joining or separating from a particular group. One final function could be to dislodge barnacles or parasites from the skin.
The region between the dorsal fin and fluke (tail) houses a phenomenally powerful muscle. This means that the whale is capable of breaching from just below the surface, and doesn’t need to dive deep beforehand to get a ‘running start’.
How do humpbacks feed?
It is thought that humpbacks find prey use their tubercles – a prominent series of bumps on the head. Each bump has a sensory hair, and it is possible that the whale uses these ‘whiskers’ to judge prey density in the water during bouts of feeding.
Humpback’s are filter feeders. The upper jaw contains up to 400 baleen plates, which strain out the water to leave the food – often krill or schooling fish. The throat opening is merely the size of a football, so only small prey can be consumed.
Humpbacks have 14–35 grooves, known as ventral pleats, that extend back to the navel. These allow the throat to expand massively as sea water rushes in during feeding.
Slapping the tail hard against the water, sometimes several times in succession, may be social or defensive behaviour. The action has been seen in response to boats approaching too closely.
Did you know?
A humpback’s wing-like pectoral fins may be smashed against the water’s surface, often together, while the whale is lying on its back. They are largely white on the underside and a third of the animal’s total body length.
Rob Lott is a policy manager at Whale and Dolphin Conservation.