Cute squirrels seen killing rivals’ young
Behaviour linked to certain years when abundant food results in more litters
Red squirrels may look cute and cuddly, but there is something dark, crafty and cunning behind those beady little eyes.
Jessica Haines, a post-doctoral fellow at the University of Alberta, found that to increase their chances of fathering pups, male red squirrels will kill the young of rival males.
While infanticide was long suspected in the red squirrel population, no researchers had witnessed it, Haines said.
That was until PhD fieldwork in the Yukon in 2014 when Haines watched an adult male red squirrel attack a pup in a case of sexually selective infanticide.
Haines’ observations are central to her scientific paper being released Thursday in the journal Ecology.
In killing competitors’ offspring, the squirrel is increasing his reproduction benefits through increased access to females, Haines said.
“They are really cute and they are really fascinating, but they also have this side where they will kill things,” she said.
Since the squirrels in the observation group are all tagged, the attack on the pup was confirmed visually and then again using genetic testing.
The male killed the pup by biting its chest and abdomen, Haines said.
That is a much different injury pattern than left by other squirrel predators. A lynx, for instance, will leave just the tail, while birds tend to pluck the squirrel before they eat it, Haines said.
What is particularly interesting for Haines is that the infanticide is linked to years of an overabundance of the squirrels’ primary food source.
Known as “mast” years, the increased production of white spruce cones triggers something biological in female squirrels that makes them increase the number of litters they have.
A typical female squirrel will have one litter per year, but in a mast year, she will have two and the second litter can be larger (females can average anywhere between one and four pups per litter).
“Even though the food doesn’t come out until the fall, they know the spring prior to that it’s going to be a good year and reproduce more in that year,” she said.
The males will attack the first litter and in doing so increase the chance of fathering babies in the second litter. When the male kills a pup, the female is more likely to breed sooner in the mast year than if her litter survives, she said.
“When infanticide happens in the mast year, it gives the males a second chance at fatherhood,” she said.