These gelada monkeys appear to have seen the benefits of pairing with wolves. Matej Hudovernik/Shutterstock

A remarkable symbiotic relationship has been found between Ethiopian wolves and gelada monkeys, with implications for how humans formed their special bond with dogs.

While Gelada monkeys (Theropithecus gelada) live in a fairly small part of Ethiopia's grasslands, there are around 200,000 of them that graze on grass and seeds in large herds.

Ethiopian wolves (Canis simensis), on the other hand, are very rare. With only a few hundred left, they are considered Africa's most endangered carnivore. The survival of the wolf may rest on the unusual relationship it has formed with the monkeys.

The wolves feed on small mammals, particularly rodents that inhabit similar territory to the monkeys. While a fully grown gelada is too large a meal for the wolves, an infant is certainly dinner-sized. Yet when a wolf enters a gelada herd, the monkeys show little concern.

In the Journal of Mammalogy , Vikek Venkataraman of Dartmouth University and co-authors report that in a sample of encounters, the monkeys didn't bother to move upon a wolf's arrival 68% of the time. And even when they did move, it was often such a short distance that they were clearly not fearful for their young. The wolves and monkeys often spent more than an hour in each other's company without conflict. However, if geladas catch sight of a dog, they will flee to their sleeping quarters in caves.

So why do wolves pass up the opportunity to eat young geladas? The authors report that two-thirds of wolf hunting sessions were successful when surrounded by the monkeys, but this dropped to a quarter when on their own. The reason is unknown, but the researchers suggest two theories: The presence of the monkeys may affect the rodents' capacity to spot an approaching wolf and take evasive action. Alternatively, the grazing monkeys may flush out the rodents from their hiding places.

Clearly then, the wolves gain a benefit from being around the monkeys, one they are wise not to put in jeopardy by ungraciously eating their hosts' young.

It is likely the monkeys also profit. The rodents are competitors for their major food sources, so a predator that keeps their numbers down is probably useful to have around.

Cooperation between animal species is common, but as the paper notes, “While mixed-species associations are common among mammals, those involving carnivorous predators and potential prey species are seldom reported.”

Humans have benefited enormously from our alliance with a different member of the Canis genus, but given our long-standing hostility toward wolves, we're not sure how, or when, the first rapprochement occurred. The adaptive strategy between these monkeys and wolves suggests something similar may have happened for humans and dogs.

Geladas are occasionally referred to as bleeding heart baboons. The name comes from the bright red hourglass shape on the males' chests. And as it turns out, these 'bleeding hearts' might just be saving an endangered African species.