A new study published in the journal Evolution reports that the bones have actually continued evolving. The two whales were caught in the act by a team of marine biologists studying their behaviour off the south Argentine coast near the province of Chubut. If the pelvis evolved to aid in reproduction, the researchers hypothesized, then it would get bigger to support a larger reproductive organ. Females are much more thick-skinned than males, enabling them to handle the onslaught. Despite the whale's size, scientists have trouble locating and studying the cetacean in the vastness of the ocean, leaving many questions about the mammal's life history, particularly its mating and courtship behaviors. If you want to feel lighter, weigh yourself in the pool. Blue whales are known to produce vocalizations , which likely have "some kind of reproductive function," said Catherine Berchok, a cetacean researcher with the National Oceanic and Atmospheric Administration. If the whole skeleton got bigger, the ribs would have been larger, too. In fact, it is one of the best whale watching destinations in the world. The actions were recorded on the Yellow Maine, which is a semi-submersible boat that is also popular with tourists. Females also give birth in the water, which helps when your babies weigh up to pounds 50 kilograms. Scientists had previously thought that whales only mated once every four years The fourth year was considered the time of copulation for females, and it was believed that the whales therefore had sex only once every four years. And the double-blubber act which was caught on video has caused them to revise their research because up until now they believed whales only copulated every four years.