Here's a fun fact: A humpback whale's penis can be up to 10 feet long.
Getting a glimpse of the impressive appendage, however, is surprisingly rare, which is why marine biologists at the Hawaii-based Pacific Whale Foundation were downright giddy when they recently spotted a whale swimming off the western coast of Maui with his junk out.
Stephanie Stack, a research biologist for the foundation, said that her team was taking a lunch break after a routine morning survey in January when they noticed a competition pod, which consists of one adult female and a group of males that aggressively compete for the chance to mate with her.
Not much is known about whales' sexual behavior, Stack told The Huffington Post, so she and her colleague Jens Currie put their pole-mounted GoPro cameras into the water to get footage of the pod.
They were able to record the "penis extrusion," when a whale is swimming with his penis out (seen at 1:10 in the video above). On Monday, Stack published a blog post on Pacific Whale Foundation's website, detailing their discovery.
"A humpback whale penis can be up to 10 feet long and is normally concealed inside the animal’s genital slit," Stack wrote. "Seeing the penis extrude from this slit is a rare sight, which is why we were so astonished and pleased about the footage."
The penis extrusion documented by Stephanie Stack and Jens Currie.
Although Stack and Currie aren't the first to film a whale swimming with his penis out, Stack said the opportunity "doesn't happen very often."
It is expensive and extremely difficult to document whales' sexual behavior. Researchers have not yet filmed whales having sex or giving birth so footage of the competition pod was monumental for the foundation's researchers, Stack said.
"We were really excited when we [saw the penis] after the fact," she told HuffPost. "We aren't specifically studying sexual behavior [so this discovery] was just sort of a happy mistake."
Stack said she thinks the whale was actually directing its sexual act toward another male, though she can't confirm that yet. If the recipient of the humpback's attention was a male, "it [wouldn't] necessarily be reproductive behavior," she explained. "It might be some form of aggression, or maybe the whale was excited due to the competition that was going on."
The whale as it approaches another whale with its penis extruded. Stack thinks the whale was approaching another male whale.
Stack is now in a year-long process of writing a scientific journal article that will explain the footage and what it might reveal about humpback whales' reproduction behaviors.