First-ever photos show humpback whales mating—and they’re males

Huge, charismatic creatures such as the humpback whale may seem well studied, but scientists are revealing new and fascinating behaviors about them all the time. 

Just a few months ago, experts released the first-ever footage of a humpback whale birth.

And now, there's another breakthrough: The first-ever observation of sexual behavior between humpbacks.

The twist? Both animals were male, according to a study published February 27 in the journal Marine Mammal Science. 

The discovery is the result of two citizen scientist photographers, Lyle Krannichfeld and Brandi Romano, being in the right place at the right time on a boat off Maui.

“They shared the photos with me for my opinion, and when I saw them, I was just stunned,” says study leader Stephanie Stack, a researcher with the Pacific Whale Foundation based in Maui. 

“Humpback whale copulation has never been seen or documented before anywhere in the world,” Stack says. (Read about a humpback whale named Frodo, who swam halfway around the world.)

“So that’s a very special and amazing encounter.”

Decades of whale tales

Because humpbacks “live their lives underwater, a lot of what they do is still very mysterious to us,” says Stack.

In recent decades, though, researchers have followed and studied these animals like never before, aided by new tracking technologies and drones. It’s also been helpful to have more eyes on the horizon, thanks to eager tourists and citizen scientists with cameras.

Longitudinal studies, which seek to follow the same animals across decades, are another invaluable asset. (Read how humpback whales may face a major setback due to climate change.)

The Pacific Whale Foundation has been studying the same group of humpback whales in Hawaii since 1980, says Stack, “and we have one of the largest photo ID catalogs in the world of individual humpback whales.”

Fortunately, the two whales involved in the sighting were already registered in the catalog as #PWF-NP_5016 (deemed Whale A in the study) and #PWF-NP_3754 (Whale B). This information allowed Stack to confirm that both whales were adults, and Whale A was also male.

Whale B’s sex was more obvious, since its penis was visible. (When not engaging in such activity, humpbacks typically keep their genitalia hidden inside a genital slit.)

The two whales copulated, with each session lasting less than two minutes. 

Same-sex behavior in animals

A recent study in the journal Nature showed same-sex sexual behavior occurs in at least 261 mammalian species—about 4 percent of the total number of mammalian species, Jose María Gómez, an evolutionary ecologist at Estación Experimental de Zonas Áridas in Spain, says by email.

"This figure is probably underestimated, because biologists have not traditionally focused on studying [same-sex sexual behavior]," says Gómez, who led the Nature study. "For this reason, studies such as the present one are very welcome."

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Scientists have observed same-sex sexual behavior in several marine species, including walruses, gray seals, Amazon river dolphins, common bottlenose dolphins, Atlantic spotted dolphins, killer whales, gray whales, and bowhead whales.

And they have just as many hypotheses for why it might occur.

Non-reproductive sexual behavior could simply be practice for future encounters, or it may play a role in establishing or maintaining a relationship between individuals. Sex could also be used to reduce tension, or as a way for one animal to assert dominance over another.

Robert Pitman, a marine ecologist at the Mammal Institute at Oregon State University who studies humpbacks as prey for orcas, puts forward an even simpler explanation.

Since adult male humpbacks in breeding grounds are focused on mating, they may try their luck with other males. Some may respond aggressively, while others, such as a sick animal, may not. 

“That seems to me to be a strong possibility here,” says Pitman, who wasn't involved in the study.

That's because Whale A appeared to be emaciated, perhaps due to a jaw injury, and harbored an unusually large number of parasitic whale lice. The animal wasn’t moving very quickly and might not have been able to swim away from Whale B, if it had wanted to. 

Million-dollar question

“Given how little we understand about humpback whale reproduction, and how much we're still understanding about their social dynamics," Stack says, "I wouldn't venture a guess as to exactly what motivated the behavior." (See 14 jaw-dropping photos of whales.)

But she and her co-authors have some additional theories. 

First, it may have simply been a case of mistaken identity on the part of Whale B. Second, it’s possible these animals had a relationship, and that the behavior was an act of bonding, or perhaps even comfort, to an ailing acquaintance. 

Stack says the reason behind the encounter remains “the million-dollar question.”

Understanding male relationships

While the study offers the first documented evidence of any penetrative sexual behavior between humpbacks—male or female—scientists have been following breadcrumbs of the behavior for years.

For example, in 1998, marine mammal researcher Adam Pack published an account of a male humpback swimming up to another male, which had died, and wrapping its pectoral fins around it with its penis visible.

“It seemed to be attempting either some type of dominance display, or maybe this was a signal for copulation, or an invitation. We didn't know," says Pack, who is full professor at the University of Hawaii at Hilo and president and research director of the Dolphin Institute. 

In 2002, Pack published another paper that found 13 incidents of males extruding their penises during 121 hours’ worth of underwater film.

And so when Pack saw the new study, he was extremely excited.

Most importantly, Pack says the observation fits into a larger conversation happening in the humpback whale research community about male relationships.

“So it's trying to like piece all these nuggets together to tell a story,” says Pack. “This is one piece of it.”