Red squirrels store food in the ground that they can access whenever they need it. When they die, the squirrels typically leave large quantities of uneaten food behind that can be inherited by whichever red squirrel moves into its territory.
“It’s like buying a home and finding a big pile of money buried in the walls,” said Andrew McAdam, an integrative biology professor at the University of Guelph. “The previous owner of where you live can significantly impact how well-off you are, at least in the squirrel world.”
In a long-term study of hundreds of red squirrels in a white spruce forest in the Yukon, McAdam and postdoctoral researcher David Fisher calculated the quantity of food stored in the ground by each squirrel. They also measured the reproductive outcomes of young squirrels that took over territories previously controlled by red squirrels that had disappeared. Some food-storage middens grew to the size of large rooms and contained as many as 20,000 cones, which remained edible for several years. One midden was active for more than 30 years and was controlled by 13 different squirrels during that time.
The study revealed that male red squirrels typically have about 1,300 more cones stored than females, and those in the prime of their lives – about age three or four – are likely to have stored many more cones than younger or older squirrels. So if a squirrel inherits a territory from a male that died in its prime, that squirrel inherits a much larger store of cones than squirrels that inherit from females or from old or young males.
“If a female is lucky enough to take over prime real estate, then she will have lots of food, which allows her to breed earlier,” McAdam said. “This means her offspring will leave the nest early, and they will have improved survival rates. Essentially, it will improve this squirrel’s genetic contribution to the next generation.”
According to McAdam, these findings illustrate how one squirrel’s food-hoarding behavior can affect the chances that another squirrel will survive, prosper, and reproduce, even if the squirrels had never previously interacted.
Unlike those in the Yukon, red squirrels in forests in the Northeast are more likely to be scatter hoarders: they bury their food in numerous locations throughout their territory rather than in one central midden. As a result, squirrels that inherit territories in the Northeast typically benefit less from their predecessors’ food stores because the cones are not as easy to find.
“One reason why individuals might not put all of their food in one place is if they can’t defend it anymore,” McAdam said. “It’s possible that squirrels in the Yukon can defend their food in one place, whereas for whatever reason squirrels in the Northeast can’t. So instead of putting all their money in one account, they stash some in the mattress and some in a book and some in a couple of different bank accounts. That’s a question that needs to be explored further.”