Rats can make friends and choose who they want to avoid, according to new study

Male rats have the ability to carefully decide who they spend time with in groups – and who they most want to avoid, a new study has shown.

The research, conducted by scientists at the Universities of Portsmouth and Lincoln, also found that the rodents tend to have preferred partners in their so-called mischiefs.

Experts said they were surprised by the findings following previous studies, which concluded female rats were reluctant to form friendships with other females.

Despite there being “limited evidence available on social behaviour in rats”, as one of the researchers noted, the notably different findings in males and females suggests the former share traits with animals such as baboons and horses.

“Discovering that male rats don’t associate with other rats randomly, but seek out their preferred cage mates and actively avoid others, shows that rats are similar in this respect to other species like birds, primates and bats,” Dr Leanne Proops, from the University of Portsmouth’s Department of Psychology, said.

Meanwhile, Dr Teresa Romero, from the University of Lincoln’s School of Life Sciences, added that “what’s particularly interesting about this work is that it contrasts to the limited evidence available on social behaviour in rats, and therefore has important implications for the management and welfare of captive rat populations”.

Dr Romero said scientists have known “for some time that animals like baboons, horses and house mice form same-sex friendships, which positively affects their reproductive success and their lifespan”, but the same could previously not be said for rats.

“Despite 150 years of breeding rats,” she explained, “we still know surprisingly little about their natural social behaviour or organisation.”

The researchers made their findings – which were published by the University of Portsmouth – by video recording 27 male rats, separated into four groups, over a three-month period, as they went about their day-to-day lives.

Crucially, the rats were observed not just at night but during daylight hours – when they are also social. While the rodents tend to be described as nocturnal, they are actually active during the day as well, the experts said.

They then used the footage to observe – every two minutes – whether the rats were in close body contact, near each other while resting, or having friendly interactions with one another.

The researchers also assessed how stable these preferences were by comparing with whom rats spent time with at the beginning and at the end of the study.

A key finding was that male rats – again, unlike females – could maintain these social preferences over a long period of time, which in some cases they did for months at a time.

“There are more than 20 million domestic rats across the world, with same-sex housing often being the norm for pet rats, and our results can have important implications for the management and welfare of these populations,” Dr Proops said about the study’s findings.

Animals have long been known to develop social preferences for particular group mates for a variety of reasons. Coatis – racoon-like mammals – become friends with those similar in age, for instance.

Meanwhile, rats are considered highly social animals that become attached to each other, love their families and are able to bond with their human owners.

It is believed they are capable of empathy and can recognise and react to pain in others, according to animal rights organisation Peta (People for the Ethical Treatment of Animals).

In fact, a paper published in the Current Biology journal last year found that rats practise the same “harm aversion” – purposely avoiding hurting someone else – that humans do.

As part of the research, a team of neuroscientists, from the Netherlands Institute for Neuroscience (NIN), gave rats a choice between two levers they could press to receive treats.

Once the rodents developed a preference for one of the two levers, the researchers rewired the delivery system so that pressing the preferred lever also delivered an unpleasant electric stimulation to the floor of a neighbouring rat – leading to shocked neighbours squeaking in protest.

As soon as a rat realised it was causing harm to someone else in its group, though, it would stop using the preferred lever – even if it meant sacrificing a treat, experts said.

“That humans and rats use the same brain region to prevent harm to others is striking,” Dr Valeria Gazzola, one of the senior authors of the study, said at the time.

“It shows that the moral motivation that keeps us from harming our fellow humans is evolutionary old, deeply ingrained in the biology of our brain and shared with other animals.”