SYDNEY, July 6 (Xinhua) -- Southern right whale mothers may rest upside down to limit nursing so they can save much-needed energy during the demanding calving season, new research has found.
Southern right whale mothers fast through the months-long calving season, relying on stored energy to give birth, nurse their calves, and travel thousands of kilometers back to feeding grounds, according to a statement from the University of Western Australia (UWA) released on Monday.
Scientists from UWA and Aarhus University in Denmark used drones to record dozens of mother-calf pairs at the protected Head of Bight calving ground off the South Australian coast to better understand the "perplexing tendency" of southern right whales to rest upside down, the statement said.
The findings, published in Mammalian Biology, showed that whale mothers spent about 33 percent of their time resting, while their calves rested around 13 percent of the time.
Notably, around a quarter of mothers often lay upside-down -- bellies to the sky -- as they rested at or near the surface, a behavior not previously recorded in other large whale species, said researchers, adding they observed it only in lactating mothers and one heavily pregnant whale.
The study found that nursing decreased as upside-down resting increased, suggesting the posture may help mothers restrict calf access to mammary slits and manage energy reserves.
"Upside-down resting may also be a way to prevent overheating, given southern right whales lack the dorsal fin which other marine mammals, such as dolphins, use to regulate their temperature," said Renae van Noort from the UWA Oceans Institute and School of Biological Sciences.
However, the behavior may increase vulnerability to vessel strikes -- a leading cause of death in right whales -- as whales take longer to "rotate to breathe and swim away quickly" if a threat approaches. Scientists advise ssels to slow down and keep a distance when whales are present. ■
