Male rats choose carefully who they spend time with – but females are less fussy, according to new research.

Scientists from the universities of Portsmouth and Lincoln have found that male rats have preferred partners in their groups and they decide which individuals to avoid.

But previous research has shown that female rats do not form friendships with other females.

Dr Leanne Proops, from the University of Portsmouth’s Department of Psychology, said: “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.”

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 Teresa Romero, from the University of Lincoln’s School of Life Sciences, added: “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.”

For the study published in the journal Scientific Reports, the researchers observed the behaviour of 27 male rats in four groups during a three-month period by video recording them while they were in their enclosures during daylight hours.

Although rats have been described as primarily nocturnal, they can also be active during the day.

The researchers observed every two minutes whether the rats were in close body contact or near each other while resting or having friendly interactions.

They also assessed how stable these preferences were by comparing with whom they spent time at the beginning and at the end of the study, and found that male rats can maintain these preferences over time, including over a period of months

Dr Romero said: “We’ve 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.

“Yet – despite 150 years of breeding rats – we still know surprisingly little about their natural social behaviour or organisation.”

Dr Proops added: “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.”