full story, comments, photos:
It's the first time scientists have found direct reciprocation
in the animal kingdom.
Norwegian rats emerge from a hole in Oregon.
Photograph by Michael Durham, Minden Pictures/Corbis
Published February 24, 2015
Rats can remember acts of kindness by other rats--and treat them accordingly,
a new study says.
In experiments, Norwegian rats were most helpful to individuals that had
previously helped them--perhaps to try and secure their assistance again,
are known to cooperate and assist one another, rewarding another rat for no
immediate gain wasn't thought to be common behavior. (Also see
"Rats Show Regret After Wrong Choices, Scientists Say.")
February 24 in the journal Biology Letters, suggests otherwise.
In fact, a rat rewarding a fellow rat for help--an act called direct
reciprocation--is a first among nonhumans, said study co-author
Michael Taborsky, a
behavioral ecologist at the University of Bern in Switzerland.
The study was based on female captive Norwegian rats' preferences for two types
of food: bananas and carrots. For these wild-type rats, bananas are a
favorite--carrots, not so much.
In the experiment, each of a pair of rat helpers could deliver one of these
tidbits to a rat in another enclosure by pulling on a stick. (Watch
a video of rats at night.)
Eventually, the receiving rat would recognize each helper as either a
high-quality helper (if it delivered bananas) or a low-quality helper (if it
Then, scientists switched the rats' places, so the rats on the receiving end
were now able to pull on a stick that would deliver cereal flakes to a certain
The rats that had given bananas generally received cereal more quickly and more
often than carrot-givers. In the same vein, the rats that had given carrots got
cereal less often than the banana-givers did.
But are the rats really rewarding helpers for their generosity?
Researcher Taborsky thinks so, adding that the rats are making a simple
"Two elements are involved: recognizing an individual, and responding to the
quality of service," Taborsky says.
The latter, he says, is evident from previously known behavior--rats will flock
to good feeding spots, for example. And recognition, he points out, is widely
documented in many species, including rats. (See "Rat
Made Supersmart-Similar Boost Unsafe in Humans?")
Since Norwegian rats exchange favors, a desire to reward others--and perhaps to
ensure more exchanges in the future--"might not be as complex as we think," says
An even simpler explanation is that the rats simply "associate the [helper] with
the preferred food,"
Thomas Zentall, an animal behaviorist at the University of Kentucky in
Lexington, said in an email.
That is, the rat associates bananas with the presence of the banana-giver, and
thinks pulling on the stick when the banana-giver is present might bring
But Taborsky argues this isn't the case, since it's known that rats can tell
they're delivering food
to another rat, not themselves.
In his view, rats clearly use the quality of service they receive to determine
how much they give back.
Wonder what that says about their tipping habits?
Follow Ralph Martins on