Whispering southern right whale mothers and calves seek refuge in surf
A team of researchers, including Lars Bejder from the Marine Mammal Research Program at the University of Hawai‘i at Mānoa School of Ocean and Earth Science and Technology, recently published their discovery that southern right whale mothers and their calves shelter in the noisy surf, stay in close proximity and effectively whisper—calling softly less than once per dive—to avoid attracting any unwanted attention.
Most mammalian new mothers are fiercely protective of their precious offspring. Even 15 to 30-foot-long southern right whale calves are vulnerable to attack by voracious killer whales. Whale mothers and calves often try to hide from predators by gravitating to cloudy water. But the loss of visual contact could force mothers and their young to call to each other more, increasing the risk of attracting the wrong attention.
The team knew that humpback whale mothers resort to whispering to their young to protect them from harm. They travelled to Flinders Bay, off the southern tip of Western Australia where southern right whales breed, and decided to listen in on the conversations between mothers and their calves, to find out how they go unnoticed.
They eventually located the females with their calves in the surf zone close to shore, which puzzled the researchers. Why were the mothers taking refuge in the most turbulent water? Were the crashing waves providing acoustic cover? And would the mothers and their offspring call to each other more frequently in the stirred-up water to keep in touch?
Stealthily approaching the whales while they rested at the surface, the team attached sound recording tags to the youngsters and their moms in the hope of recording the pair’s interactions. After successfully tagging nine whale mums the team recorded almost 63 hours of conversation as the mothers and calves sheltered in the surf.
“It was difficult to assign the calls to either the calf or the mom, because they are so close to each other,” said lead author Mia Nielsen from Aarhus University, Denmark.
So instead she assigned the calls to the calf-mother group. Although it was clear that the animals were producing two types of calls, a grunt and a mooing sound, the team was surprised when they realized that instead of communicating continually the mother and calf called less than once per dive. And when the researchers analyzed the sound volume of the animals’ calls, they were surprised by how quiet the moos and grunts were. The pounding waves drowned out the calls within a few hundred meters, making it difficult for killer whales to eavesdrop on the soft conversations between the close pairs.
The authors suspect that the whales’ unconventional choice of location in the crashing surf could conceal and protect them from unwanted attention.
Read more on New Scientist, Science News, Independent and Eurekalert.