Scientists analyzed a database of more than 450,000 images of whales in the wild to track the animals. They found that some swam thousands of miles during the mating season.
Two distinctive males, which could be recognized by markings on their tails, were recorded at two popular mating locations within two months of each other.
The first was off the west coast of Mexico and the second was near Hawaii, about 3,700 miles (5,955 kilometers) apart.
The timing suggests the whales swam faster than their typical cruising speed of 2.5 miles (5 kilometers) per hour to get there.
“Our first reaction was, ‘You’ve got to be kidding me! “, James Darling of the Whale Trust Maui in Hawaii and author of the study told New Scientist magazine.
“They may just be traveling on the ocean as if it were their own backyard,” he said.
The findings were published Wednesday in the peer-reviewed journal Biology Letters.
North Pacific humpback whales tend to spend their summers around Canada and Alaska before moving to breeding grounds near Mexico and Hawaii in winter.
They do not mate for life and it is thought that females seek a new mate each breeding season.
Scientists previously assumed that they would choose a mating site. But, thanks to distinctive tail markings, scientists saw that one male had traveled 2,824 miles (4,545 km) from Maui, Hawaii, to the Revillagigedo archipelago in Mexico between February 23 and April 17, 2006.
The second made the reverse journey from Guerrero, Mexico, to Maui between February 16 and April 5, 2018, a journey 3,693 miles (5,944 km) long.