Making friends and acquaintances is not a random act for kangaroos, instead they actively choose who they mix with and how often.
Female eastern grey kangaroos have been shown to spend time with some other females while avoiding others altogether.
Kangaroos live in a fission-fusion society, characterised by frequent changes of group membership, with individuals moving between temporary feeding groups and switching groups many times a day.
This gives an individual kangaroo the opportunity to decide who they are with at any time.
Now scientists have found that personality traits such as boldness and shyness can determine how sociable a kangaroo is.
Shyer, or risk-averse kangaroos feed in larger groups than bolder or braver individuals.
However, bolder risk-taking kangaroos have more 'friends' – other kangaroos they go out of their way to spend time with – than shyer ones.
Researchers from the University of Queensland, Australia, wanted to find out what kangaroos might get out of developing friendships and the benefits of being sociable or not in a species which is not highly cooperative.
“Why should kangaroos show these ‘friendships’ when in fact they don’t seem to do anything for each other?” said Dr Anne Goldizen, one of the authors.
“They don’t help with each other’s young, cooperatively defend resources or even groom each other.”
The findings, reported in the journal Behavioral Ecology, were made in a population of eastern grey kangaroos (Macropus giganteus) at Sundown National Park, Queensland that has been studied since 2009. Two thirds of the population are female so males were excluded from the study.
Feeding groups as well as individual kangaroo’s associations with other kangaroos were observed and recorded during an 18 month period.
To measure boldness, or risk-taking, one of the research team walked towards a kangaroo until it fled. The kangaroos that allowed a person to get the closest were considered to be bold and shyer females were those that fled the quickest.
Individuals in larger groups are safer from predators
According to the authors, this is the first time that the relationship between boldness and sociability has been studied in wild mammals.
The research team think that shy kangaroos are less choosy about who they mix with and gather in larger feeding groups than bolder females because they perceive this to be a safer, less risky option.
“We suspect that shy females prefer to be in larger groups because individuals in larger groups are safer from predators,” said lead author Dr Emily Best.
“We also suspect that shy ones are less selective of acquaintances because to be selective would require an animal to spend more time leaving groups to search out those acquaintances, and an inherently more risk-averse individual might find that a risky thing to do.”
Follow Zoe Gough on Twitter and BBC Earth on Facebook, Twitter and Instagram.