Australasian Science: Australia's authority on science since 1938

Joeys Neglected When Mums Mingle

Having a social life comes at a cost for grey kangaroos, with research published in Behavioral Ecology and Sociobiology finding that joey survival is lower among mingling mothers.

Lead author Dr Wendy King of The University of Queensland’s School of Biological Sciences said young kangaroos that spent more time with their mothers grew faster and gained more weight than other joeys of the same age, and were more likely to survive to adulthood.

“For kangaroo sons, spending time with their mother correlates closely with receiving milk, and so sons are likely to benefit nutritionally from this extra maternal care,” King said. “Some daughters, however, associate closely with their mothers even if the mother no longer provides milk, and must benefit in other ways.”

King said that grey kangaroo mothers did not defend their young from aggressive adult females, but mothers could reduce harassment of their offspring just through their presence. “Juveniles feeding alone with their mothers do not need to compete with others for food, and have more time to feed and grow more rapidly,” King said. “However, mother kangaroos rarely interact with their young through activities such as playing and grooming, so it is unlikely juveniles benefit from behavioural development or parasite removal.”

Co-author A/Prof Anne Goldizen said the findings suggest there is a cost to being sociable for female kangaroos. “That cost may relate to young more easily losing their mothers when in a large group,” she said. “This cost of being social raises the question of why kangaroos usually forage in groups.”

The study of 129 kangaroo offspring aged 10–21 months took place over 6 years at Wilsons Promontory National Park in Victoria. While previous studies have investigated the links between mother–offspring relationships and offspring growth and survival in mammals, none have done so in marsupials. King said the mother–offspring bond in macropods such as kangaroos appeared to be quite special.