It’s common for social animals to adopt and care for orphaned offspring. According to ScienceDaily, other loner species — like squirrels — may be learning such altruism.

In yesterday’s Daily Briefing, MNN touched on this story saying, “A team of Canadian researchers have discovered squirrels will sometimes adopt related pups that have lost their mother, revealing a soft side of the arboreal rodents that scientists previously hadn't seen.”

Evolutionary biologist and professor Andrew McAdam, from the University of Guelph in Ontario, Canada, along with researchers from the University of Alberta and McGill University were the scientists behind the study.

McAdam said, “Red squirrels live in complete isolation and are very territorial. The only time they will allow another squirrel on their territory is the one day a year when the females are ready to mate or when they are nursing their pups.”

Yet the study, published in Nature Communications, found that squirrels adopt orphaned pups if they are related … but even that is a rare occurrence.

How rare? McAdam and his team found five cases of adoption in more than two decades of research. But ScienceDaily says, “Jamie Gorrell, a PhD candidate at the University of Alberta, identified 34 cases of potential adoption over 20 years. An adoption is possible only if the mother dies and a nearby squirrel is also nursing.”

But even by that slightly higher standard, 34 cases out of the thousands of litters over the course of 20 years proves that the squirrels rarely adopt.

According to McAdam, relatedness plays a critical role in the decision by a neighboring squirrel to adopt. In the five examples in his study, the pups were nieces, nephews, siblings, or grandchildren to the adoptive mother.

"From an evolutionary perspective, the phenomenon of adoption raises the question of why an animal would adopt in the first place given that it jeopardizes the survival of their own offspring," said McAdam. "Under the right conditions, an animal can propagate more copies of its genes by helping relatives to raise their offspring than by producing offspring of their own. So in some cases it might be a good bet to adopt and accept these costs."

McAdam found that squirrels only adopt when the orphans carry a large percentage of the same genes, meaning that they are more likely to adopt siblings, nieces, or nephews rather than more distant relatives.

Amazingly enough, McAdam also noted that squirrels are able to assess which pups are related to them. Squirrels rarely interact with their neighbors, but an adoption may take place if they fail to hear the unique call of a nearby relative for several days, causing them to investigate. If they choose to take in the orphaned pups, they carry them back to their nest on their backs.