Two male bears have been observed regularly having oral sex at a wildlife sanctuary in Croatia.

According to a report in journal Zoo Biology, researchers from the Polish Academy of Sciences Department of Wildlife Conservation have recorded “the first observations of long‐term, recurrent fellatio in captive brown bears kept in proper conditions”.

Fellatio is rarely observed in non-human species, and is usually considered a stress response, rather than intended for enjoyment.

However, according to report, the researchers recorded 28 instances of oral sex between the two male bears across 116 hours of observations.

They wrote: “The provider always initiated the contact involving vigorous penile sucking that appeared to result in ejaculation.

“All cases appeared to be initiated by the provider, who approached the receiver while he was resting on his side or with part of his abdomen exposed. If the receiver’s genitals were not exposed, the provider would push his head into the pelvic region or use his paws to separate the hind legs.

“After accessing and initial licking of the penis, the provider would find a more comfortable posture, such as sitting or lying… once actual sucking started, neither bear changed position.”

Lead researcher Agnieszka Sergiel theorised that the unusual behaviour had developed because the bears were orphaned at an early age.

They wrote: “We suggest that the behaviour began as a result of early deprivation of maternal suckling, and persisted through life, possibly because it remained satisfying for both individuals. This constitutes the first descriptive report of fellatio in bears.

“Forced early‐weaning and subsequent deprivation of proper and sufficient stimulation of the suckling reflex can result in teat‐searching behavior persisting into adulthood.

“In the case reported here, the provider may have found a substitute for teat‐sucking that also resulted in a let‐down of substitute ‘milk’.”

(h/t io9)