Squirrels will slay babies for chance to mate: study

“Really cute … (but) they will kill things”

Red squirrels may look all cute and cuddly but there is something dark, crafty and cunning hiding behind those beady little eyes.

Jessica Haines, a postdoctoral 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 during PhD fieldwork in 2014 in Yukon, when Haines watched an adult male red squirrel attack a pup in a case of sexually selective infanticide.

Haines’s observations are central to her scientific paper, released in the journal Ecology on Thursday.

In killing competitors’ offspring, the male 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 those by 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 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 a year, but in a mast year she will have two, and the second litter can be larger (females average 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.

UNIVERSITY OF ALBERTA-JESSICA HAINES Post-doctoral fellow Jessica Haines says she witnessed this Yukon male red squirrel commit infanticide in 2014.