Two captive brown bears have been spotted enjoying oral sex, and researchers wonder if it’s because the two males were deprived of maternal suckling too soon.

Sexually stimulating behaviors that don’t lead to babies are rare among non-human (and especially non-primate) mammals. The illustrious list of animal masturbators include porcupines, walruses, squirrels, dolphins, and Adelie penginus. Those last two are also known to please themselves with dead animals. As for oral sex, female short-nosed fruit bats perform the deed, as do the famously titillating bonobos.

Now, a team led by Agnieszka Sergiel from the Polish Academy of Sciences in Krakow report fellatio among male brown browns -- the first time it’s been described in brown bears kept under proper conditions. The two unrelated bears were born in 2003 and put in a sanctuary in Kuterevo, Croatia, after being orphaned as cubs.

The researchers observed the two bears engaging in oral sex multiple times a day until they were at least 10 years old. The team logged 116 hours of observation time over six years, witnessing 28 acts of fellatio ranging between a minute to four.

One was always the giver and the other was always the receiver; the larger one never reciprocated. The smaller, giver bear would initiate contact by approaching the receiver while he was resting on his side with part of his abdomen exposed. Sometimes the giver bear would push his head into the nether regions or use his paws to separate the legs before settling into a more comfortable position.

Then, the “vigorous penile sucking” resulted in apparent ejaculation. That’s evidenced by muscular contractions and fluids on the muzzle of the provider, LiveScience reports. Afterwards, the bigger bear often pushed the other one off or turned away. As time went on, the behavior became increasing ritualized, and the oral sex wasn’t influenced when a female bear was introduced in 2010.

The researchers suggest that the behavior may be a consequence of being orphaned at an early age and likely began as a result of early deprivation of maternal suckling. Being weaned too early not only denies them of milk and sustenance, but also bonding and comfort from their mothers. That’s why some orphaned cubs would suck on the paws or ears of their siblings, as a substitute for their mother’s teats. The sex act likely persisted for several years because it remained satisfying for both parties involved.

The work was published in Zoo Biology earlier this month.

[Via LiveScience]

Image: A. Sergiel et al., Zoo Biology, 2014 Wiley Periodicals