Scientists finally have an explanation for this weird whale behavior

In the Head of Bight, South Australia, the southern right whale mother rests belly-up with her pectoral fins stretched into the air. After a few minutes, she slowly rotates so her blowhole is facing upwards, takes a breath, then swivels upside down again. Her newborn stays close by. When mom finally flips the right way up again, the baby starts nursing on her toothpaste-thick milk.  

The mystifying scene was caught on camera by drones as part of a new study. Researchers documented 15 whale mothers resting upside down this way. 

“It's just such a weird behavior,” says Renae Van Noort, a research associate at the University of Western Australia’s School of Biological Sciences who studied this strange phenomenon. “You can see it from a mile away…a little slither of the belly but then just these huge, big arms out of the water.”  

Now, in a theory published in the journal Mammalian Biology, scientists have explained why they think the females float upside down—and it might be because these whale moms need a break. 

An energy-saving strategy 

There has been no other documentation of large whale species resting upside down, so the scientists were puzzled. “We were just so stumped,” says Van Noort. 

Southern right whales are a migratory species. They feed in Antarctic or sub-Antarctic waters during summer, then travel to breeding grounds in southern Australia, South Africa, Argentina, or Chile for the winter.

When they arrive, they’re “really, really fat,” says Van Noort. They won’t eat again until they return to their Southern Ocean feeding grounds. 

“Right whales just have to stack on all this energy and then they travel this enormous distance and have a baby,” says Peter Corkeron, a right whale expert and adjunct professor at Griffith University’s Australian Rivers Institute who wasn’t involved in the study. The new mothers “then dump phenomenal amounts of energy into the baby through milk.”

Mothers lose huge amounts of weight while nursing. “The mum, she can't go to the supermarket while she's here and stock up on food,” says co-author Kate Sprogis, a lecturer at the University of Western Australia’s Oceans Institute. “The only way she can get fat again is by migrating all the way back.” 

Van Noort reviewed 75 hours of footage and noticed that, with the exception of one heavily pregnant female, only lactating moms displayed this topsy-turvy resting strategy. 

Turning belly-up could help the mother control her baby’s feeding, they say. “When she's upside down, her mammary slits are above the water, or they're just that little bit too difficult for the calf to get to,” says Van Noort. “It could be a way for [mom] to be like ‘give me a minute.’” The videos showed the more time that mothers rested upside down, the less time that calves spent nursing.

Southern right whale calves are at least four meters—about 13 feet—long at birth and rapidly pile on the pounds by drinking mum’s energy-rich milk. While nursing, the baby “grows at least three centimeters a day,” says Sprogis. Meanwhile, mum loses around a quarter of her bodyweight during the three-month breeding season. Since females can grow to around 175,000 pounds, a right whale mom could lose as many as 43,000 pounds or more—about the weight of three African bush elephants.

That weight loss can lead to energy depletion, so regulating her calf’s feeding helps a right whale mother make the long journey back to the feeding grounds. “It's not her being a mean mum and not wanting to give her milk away to a calf,” says Sprogis. “It's actually to sustain her.”

Cooling off 

But there’s one more theory floating around, and it’s that these huge whales are trying to cool down. Southern right whales lack a dorsal fin—something other whales and dolphins use to regulate temperature. “Maybe they're exposing their belly and their flippers—their pectoral fins—out of the water to increase that heat dissipation,” says Van Noort, “like dipping your legs in a pool in summer.”

Corkeron isn’t convinced by this, saying they have better ways to cool down: “Right whales have these masses of very fine capillaries in the roof of their mouth,” he says. They “can dump heat by swimming around with their mouth open and letting seawater flush their mouth.”  

Whatever the reason, the researchers don’t yet know if other southern right whale populations rest upside down or if these upturned breaks are unique to the individuals in the Head of Bight. Notably, shipping vessels are banned there during calving season, and the experts suggest it’s a strong argument for banning them elsewhere, since the upside-down maneuver would likely not give a whale mother time to get out of the way of a ship. 

If people understood the value of vessel-free zones for protecting these mother whales, they might consider them in other areas, says Corkeron: “Maybe other places in the rest of the world could look at this instead of just brushing it off as a ludicrous and impossible idea.”