It's no secret that the nature of our surroundings influences our state of mind. As it turns out, the same is true for hamsters.
Many species have been the subjects of studies about animal emotion, including horses, dogs, pigs, cats, sheep, chickens, rats, and mice. And all of these species have shown the capacity for mood-congruent judgment. In other words, all have demonstrated, to a greater or lesser extent, an inclination to expect outcomes that mirror their state of mind.
Researchers from the U.K.'s Liverpool John Moores University decided to probe the emotional depths of one of the most commonly kept creatures, hamsters, to see if, in fact, these furry little critters also show some inclination to make judgments and decisions based on their mood.
To begin the study, the researchers trained a group of 30 male hamsters (all captive-bred) to make positive and negative associations with two different water containers placed in separate corners of their cages. The hamsters were trained to associate one of the containers with a positive result (a sugary liquid), and the other container with a negative result (a bitter liquid).
Once the hamsters had been trained to make the positive and negative associations with the containers, the researchers began placing empty or full containers in various locations in the hamster cages. At the same time, they randomly replaced empty containers with containers filled with either the sweet or bitter liquid. They did this to encourage the animals to explore their surroundings with the chance of finding a tasty surprise as a reward.
At the outset of the study, all of the hamsters' cages contained a layer of aspen chips and some basic bedding, one wheel, and two cardboard tubes. After the initial training, the researchers put half of the hamsters in cages with lots of extras: extra bedding, chew toys, a tent, huts, and nicer wheels. The researchers then removed the wheels, tubes, and some of the bedding from the cages of the remaining hamsters.
The team gave both groups of hamsters several days to adjust to their new surroundings, and then reintroduced the container test with both empty and full containers, the latter holding either the sweet or bitter liquid. What the team found was that the hamsters in the deluxe cages were more inclined to approach the containers and test the liquid than the hamsters in the plain cages were.
The researchers interpreted the marked difference in behavior as an indication that the animals in the plain cages were less optimistic overall as a function of their drab surroundings. The finding was an analog of the phenomenon in the human world, whereby depressed and anxious people are less likely to expect positive things to happen to them. The researchers concluded:
"We cannot say whether the hamsters in our study felt happy in their enriched housing, 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."
This study, which was published in Royal Society Open Science, is significant in that it adds valuable evidence - and a species - to a growing body of data about animal emotion. It is also important from an animal welfare perspective in that its findings will, perhaps, encourage pet owners and laboratories to provide more than just the basics for their hamsters, since we now know that cozy hamster cages make for optimistic hamsters.