Scientists have determined the reason why female southern right whales off the coast of Australia float belly-up, as detailed in observations published in the journal Mammalian Biology. It turns out that this pose is predominantly adopted by individuals with newborn calves, rather than sick or injured animals. Each year, these mammals travel roughly 6,000 kilometers from Antarctica to the Australian coastline. In cold waters, they build up fat reserves by feeding on krill, while in warmer regions they give birth to their young. During this period, mothers barely eat, making it crucial for them to conserve energy due to the rapid growth of their calves and the high metabolic demands of milk production. Experts analyzed the behavior of 59 pairs and found that about 25 percent of mothers regularly roll onto their backs, remaining in this position for up to 20 percent of the observation time. Researchers suggest that this posture physically blocks the calf’s access to the mammary glands, allowing the female to rest and regain strength without constant nursing sessions. The sole exception in the study was one individual in the late stages of pregnancy. Another hypothesis relates to thermoregulation. Southern right whales lack a dorsal fin, which in many marine creatures helps dissipate heat. The belly-up stance exposes the abdomen and pectoral flippers to cool winds, enabling the animals to effectively cool down in warm coastal waters. The authors of these theories emphasize that such rest makes these enormous females vulnerable, as they need extra time to flip over and submerge in the event of a sudden approach by vessels.
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