Hamsters happier when in hammocks, study finds
Happiness is a hamster swinging in a hammock, according to the first study to measure the mood of the cuddly rodents in an objective way.
When their cages were kitted out with hammocks, extra bedding, ledges, chew sticks, and plastic "hut" shelters, the little animals displayed mental states similar to those seen in happy people, the research showed.
An enriched environment made them more optimistic - just like "glass full" humans who look on the bright side of life.
Hamster happiness was tested by first training the creatures to choose between bitter-tasting water laced with quinine and sweet sugary water in a different location.
When an "ambiguous" drinking tube was placed between the two locations, hamsters approached it more often after enjoying the delights of an enriched cage. Those from spartan cages were less likely to try their luck.
Stimulated hamsters appeared to be more hopeful about the chances of obtaining a sweet rather than bitter drink from the tube, said the scientists.
Lead researcher Dr Emily Bethell, from Liverpool John Moores University (LJMU), said: "This study shows that hamsters housed in enriched environments make more optimistic judgments about otherwise ambiguous information.
"The important note for pet owners is that ensuring pets have adequate opportunities to express natural behaviours in captivity improves their mood and is essential for their welfare."
Thirty captive-born male Syrian hamsters (Mesocricecitus auratus) took part in the study, reported in the journal Royal Society Open Science.
To begin with, all were housed in standard laboratory cages containing a thin layer of wood chip bedding, a barred running wheel and two cardboard tubes.
Enrichment consisted of suspended hammocks, hanging tents, gnaw sticks, wooden ledges, plastic huts, and a larger solid-floor wheel running smoothly on ball bearings.
The enriched cages also had a deeper layer of bedding and extra nesting material.
During the study hamsters were switched between enriched and non-enriched conditions, and this was reflected in their mood. When the enrichment was removed, they became less optimistic.
The scientists wrote: "Hamsters were more likely to approach an empty drinker at ambiguous locations when enrichment had been added to their cage for the previous week than when it had been removed.
"Hamsters approached more often as the probe neared the positive location."
It was the first time anyone had been able to demonstrate that shifts in emotion can objectively be measured in hamsters.
Co-author Dr Nicola Koyama, a senior lecturer in ethology at LJMU, said: "Judgment bias studies let us examine the effect of emotions on cognitive processes and are important measures for improving animal welfare.
"Hamsters are often a child's first pet and we've shown that what goes into a cage (ledges, chews, hammocks and material to dig in) has a positive impact on a hamster's emotional state and thus, their well-being."