Whale Calves Caught Stealing Milk From Other Mothers

Whale calves have been caught stealing milk from other mothers, new research from the University of Western Australia has found.

The new study, published in Mammalian Biology, found that southern right whale calves sometimes “allosuckle,” meaning they steal milk from whales that are not their own mothers.

“Allosuckling has been observed in seals and land mammals, including deer, reindeer and giraffe, but not quantified in large whales,” adjunct research fellow Kate Sprogis, from UWA’s Oceans Institute and School of Biological Sciences, said in a summary of the findings. “The behavior observed off the south coast of Australia appeared to be a direct and intentional movement from the calf and the non-biological lactating mother was generally evasive.”

This species of whale lives throughout the Southern Hemisphere, migrating between feeding grounds with the turn of the seasons, according to NOAA. The species’ life span is “likely similar” to that of the North Pacific and North Atlantic right whales—similar species found in the Northern Hemisphere that are thought to live for at least 70 years, NOAA says. Females give birth every three to five years, and have a one-year gestation period. The calves then tend to stay with their mothers for a year after birth.

It is easy to understand why allosuckling happens—this can provide a calf with extra milk and nourishment. However, it actually has negative effects on the biological mother as whales need to provide milk to their own offspring.

This is because the mother herself does not feed until the nursing season is over.

“[She] is not able to replenish her lost energy reserves,” Sprogis said. “And at the end of the nursing season the lactating mothers need to migrate back to their feeding grounds. For southern right whales, this is a long migration from Australia all the way to sub-Antarctic Islands or to Antarctica where the mothers can refuel their energy by feeding on small invertebrates like copepods and krill.”

These findings are important as southern right whales are endangered under the Australian Environment Protection and Biodiversity Conservation Act. Learning how they grow as calves is essential in contributing to conservation efforts.

It is likely that this behavior occurs in other whale species, but more research will be needed to determine this.

There are a number of threats facing the species, meaning their numbers are not as abundant as they once were. Until the 1960s, the species were hunted by the whaling industry which drastically depleted their numbers. Since then, the population has recovered only slightly.

Other threats include entanglement in fishing gear. If the species gets tangled in nets or rope, it can impair their ability to swim and feed. They are also at risk from vessel strikes, habitat degradation and climate change.

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