Southern right whale mothers and calves whisper to each to avoid attracting predators such as killer whales and sharks, biologists have found.
The whales feed near Antarctica during the summer and then migrate north to coastal waters during the winter to give birth and breed. The mothers and calves remain there for three months and often keep very close to shore, just beyond breaking waves.
It is suspected they do this because the noise of the waves helps mask any sounds they make and thus makes it harder for predators such as killer whales and sharks to find them. The findings of Mia Nielsen of Aarhus University in Denmark and colleagues suggest this is indeed the case.
Her team attached sensors to mother whales in Australia’s Flinders Bay to record the animals’ location and depth, and the sounds they produced. The suckers that held the sensors in place detached from the whales automatically after 12 hours, but most sensors were knocked off earlier by the calves, which stay very close to their mothers.
The team found that mother-calf pairs made fewer than ten calls each hour, and the moo-like calls they do make are relatively quiet for whales – the equivalent of whispering.
It was recently shown that humpback mother-calve pairs also whisper to each other, so this might be common behaviour in many whale species.
The southern right whale pairs also made most calls when they were active. “We suspect that the sounds are a way for them to remain in contact with each other,” says Nielsen.
It’s not clear how many calves fall victim to predators, she says. But the mothers invest a huge amount of time and energy in them, losing tons of weight during the time they nurse their calves without feeding themselves.
“It would be a huge loss just to lose a single calf,” Nielsen says.
Southern right whales have only recently returned to places like Flinders Bay. The overall population is thought to number around 10,000 and is slowly increasing.
But both the right whale species found in the northern hemisphere – the north Atlantic and the north Pacific right whales – are heading for extinction, with only a few hundred remaining. Collisions with ships and entanglement in nets are killing them faster than they are breeding.
Journal reference: Journal of Experimental Biology, DOI: 10.1242/jeb.190728
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