Hamsters Are Optimists When They Live in Comfy Cages

Hamsters have feelings, too. Just as people are inclined to interpret the world through either a gloomy or rosy lens depending on their mood, hamsters make judgments based on their emotional outlook. In the rodents’ case, however, it’s not getting a promotion at work or receiving a breakup text that determines mental disposition, but whether they have access to cage bling like hammocks, plush bedding and chew toys. 

Animal emotion is a rich field of study, and rats, mice, cats, dogs, sheep, chickens, horses, pigs and even honey bees have all demonstrated some degree of mood-congruent judgment, or the tendency to expect positive things when we’re happy and negative things when we’re down in the dumps. Until now, however, no one had investigated whether hamsters are on the same emotionally interpretive wavelength.

Untold multitudes of these furry friends are kept as pets around the world, and they are commonly used in laboratories as animal test subjects. Producing scientific evidence that wheels and chews make hamsters happier could be used to motivate both labs and pet owners to throw in a few toys and ultimately improve animal welfare. So researchers from Liverpool John Moores University in the U.K. decided to investigate.

The team first trained a group of 30 captive-bred male hamsters to associate a water container in one corner of their cage with a treat of sugary liquid and a container in the other corner of their cage with a punishment, a bitter liquid. Next, they began adding empty or full drinkers to various locations throughout the cage, and also randomly replacing an empty container with either the bitter or sugary beverage. This was meant to encourage exploration—hamsters might take a chance on a container and get a sweet surprise. The setup also helped ensure the hamsters weren’t using an external cue, such as scent, to identify which containers contained tasty payloads.

All hamsters originally had a layer of aspen chips under their feet, some basic bedding, a running wheel and two cardboard tubes. But after the drink training, the team changed up parts of the hamsters’ cages. Half enjoyed extra bedding, huts, chew toys, a ledge, a fancier wheel and a tent. The other half of the group lost their wheels, cardboard tubes and some of their aspen chips.

After several days, the researchers again presented the hamsters with the water container task, including empty containers as well as those with sugary or bitter liquids. As they report this week in the journal Royal Society Open Science, the hamsters who had been living the good life in the enriched cages were significantly more likely to take a chance on approaching the extra water containers than those that had been spending their time in the stark, joyless cages. The team thinks that, like depressed and anxious humans who expect all events to turn out negatively, hamsters that had spent time in the boring enclosure seemed less optimistic about the chances of something positive—in this case, uncovering a randomly placed container of sugary water—would actually happen to them. 

“We cannot say whether the hamsters in our study felt happy in their enriched housing,” the researchers write, “but the changes in cognitive processing of ambiguous cues certainly suggests enriched hamsters became more optimistic about the likelihood of future reward when faced with uncertain information.”

While the exact nature of animal emotion evades us for now, the researchers point out that the hamsters’ shift in behavior was strikingly similar to that of humans with corresponding emotional circumstances. Just as entertained and engaged people are usually more upbeat, fun toys, interesting obstacles and fluffy bedding seem to make for a happy hamster state of mind.

Rachel Nuwer | | READ MORE

Rachel Nuwer is a freelance science writer based in Brooklyn.