This article is from the WSSF 2015 AFRMA Rat & Mouse Tales news-magazine.

By Marlene Miller, D.V.M., Texas

RE: Putting her rat Barkley with new babies that came from the same breeder as him. The other rats she tried before this were from a different breeder.

Q I would not have believed this but Barkley was calm and looked almost interested when he first saw the babies. With the others his expression was horrified and he wouldn’t even get near.

When I moved the cage in his room, Barkley started sleeping in the hammock closest to their cage. He never used the hammock before they came. First intro in play area the babies chased him, jumped on his back and grabbed his fur under his head, and he did nothing! Second day together in neutral play area I found them all squished onto a small ledge with the babies stacked on top of Barkley. And tonight I found him grooming them. Today’s only the second day. Completely different reinsert to the babies. Do you have any reference to how they are recognizing? Is it some sort of phenomenon with all rodents that live in colonies? I wonder if it’s just simply smell.

A I’m not sure but rats from the same colony/breeder recognize they are with friends and many people have found they integrate together well where trying to introduce rats that are not related in any way sometimes one can never get them to get along no matter how old they were when brought in. That is why when I sell rats to people, they have to get at least 2 (and of the same age) so they are with their own kind. Karen Robbins

Update: Here’s what I have found. The evolution of social recognition is necessary for survival of the species (determining friend from foe I guess).

Each individual has its own urinary protein profile which is genetically determined. That’s how they identify their own urine mark vs. an intruders. Since genetics determine the major urinary proteins, they are identifying kin by similarity to their own pee.

This is what makes sense to me. Also, odor receptors (what you have the ability to smell is genetically determined), so not only does their pee have a similar protein profile but their ability to smell that profile is similar. Marlene Miller, D.V.M.