Humpback whales are known for their impressive migrations—traveling thousands of miles from polar feeding grounds to sheltered tropical waters to breed. It is believed that calving habitat in Australia is distributed no farther south than 23 to 28 degrees south latitude. But this might not be the full picture, according to a study published in Frontiers in Marine Science.

The paper used data from citizen scientists, government surveys and stranding reports to explore where humpbacks give birth around Australia and New Zealand. “Hundreds of humpback calves were born well outside the established breeding grounds,” says author Dr. Tracey Rogers of the University of New South Wales. Meaning that humpbacks can give birth in colder water than once thought, and some mother and baby pairs continued to travel along the migration route toward tropical waters.

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Having babies outside typical breeding grounds could put the little ones in harm’s way, Rogers explains: “Giving birth along the ‘humpback highway’ means these vulnerable calves, who are not yet strong swimmers, are required to swim long distances much earlier in life than if they were born in the breeding grounds.” It is not yet clear why whales continue to migrate, an energy-intensive task that leaves calves vulnerable to predation, if they can give birth closer to the poles.

The authors think this observation could be due to a boost in numbers or more eyes (and cameras) on the water rather than a behavioral change. “I think it’s very likely that this pattern has always existed, but the low number of whales obscured it from view,” says author Jane McPhee-Frew.

“The Eastern Australia humpback population narrowly escaped extinction, but now there are 30, 40 or 50,000 in this population alone.” The authors say expanded protected areas and further research are needed.