Even after young kangaroos move out of their mother’s pouch, spending time with her pays off. New research links the time they spend with mom to better ability to feed themselves and survive to adulthood.
The results, published in the journal Behavioral Ecology and Sociobiology, surprised the researchers because, unlike primates, kangaroo mothers rarely groom or interact with their young, and their so-called “young-at-foot” don’t really need to be shown how to chew grass. But there is just something about being with mum that helps their young-at-foot survive.
Lead researcher and biologist Wendy King suspects that the presence of a mother may be crucial in protecting young-at-foot from harassment from other adult females, keeping them safe from injury, and giving them time to eat in peace.
“What we found is that the amount time offspring spend with their mother is really important. The more time they spend with their mother, the heavier and bigger they are getting even though they are no longer suckling,” says King, a visiting scholar at the University of Melbourne, who conducted the research for her PhD at the University of Queensland and is now based at Université de Sherbrooke in Quebec, Canada.
“I suspect that what may be going on here is that offspring who are close to their mother are less subject to interference or harassment from adult females.
“Other adult females will growl and claw at young-at-foot that don’t belong to them if they get too close,” she says.
Watch mom teach young chimps to use ‘termite tools’
King and colleagues from the University of Melbourne spent six years studying a population of eastern grey kangaroos in Wilsons Promontory National Park on Australian’s rugged south eastern coastline. They tagged both mothers and their joeys, and then relentlessly observed them in the wild.
King herself spent five hours every day for 10-12 days a month over a period of 27 months watching the kangaroos through binoculars and keeping careful track of the distance the young would wander from their mothers. The researchers also periodically recaptured the kangaroos and weighed them. In all, 129 young-at-foot were tracked between the ages of 10 months and 21 months, which is the age at which they become nutritionally independent.
Kangaroos only emerge permanently from their mother’s pouch at age 10 months, but then spend a further 8-11 months periodically suckling as young-at-foot.
The researchers measured an offspring’s time spent with its mother, both when mother and young were together as part of a larger group and when they were just with each other.
These social animals inherit friends from mom
They found that those who spent more time with their mother were around 6 percent larger and 19 percent heavier at two years old. But additionally, those that spent more “quality” time alone with their mother had higher survival rates.
That would support the idea that young-at-foot benefit from being kept away from other females, while the presence of the mother still helps to signal dangers like predators.
“It provides an opportunity for offspring to feed calmly with their mothers away from other adult females,” she says.
But while it makes good sense for independent young to stay near their mothers, the researchers found that there was a huge variation in their behavior. While some were always with their mother, others were happy to wander off for long periods, only spending 20 percent of their time with their mothers. The latter tended to be males.
The researchers defined an offspring as being “with” its mother when it was within 10 meters of her, or within 10 meters of a group including the mother.
The study, which is ongoing, also found that climate has a huge influence on juvenile survival. In the first cohort of young-at-foot studied, the survival rate from permanent pouch emergence to 21 months of age was 75 percent, falling to 59 percent for the second cohort. But for the third cohort, which developed during a time of drought, the survival rate was just 21 percent.
Source: University of Melbourne
