Evaluation of Locomotor Activity in Group-Housed Hamsters: Effects of Cage Size and Running Wheel Availability

In the world of animal welfare, the question of how much space a creature needs is often a matter of debate between what is practical for a keeper and what is natural for the animal. For the golden hamster, a popular pet found in shops across Japan, the reality is often a compromise. While these animals are naturally solitary and fiercely territorial, commercial constraints frequently lead to them being kept in groups within relatively small enclosures. This practice raises concerns among scientists and caretakers alike: does crowding these independent animals together, combined with limited floor space, suppress their natural urge to move and explore? To understand the impact of their environment, researchers look at two main variables: the size of the cage and the availability of a running wheel. A running wheel is a simple device that allows an animal to run in place, mimicking the long distances they would cover in the wild. Previous studies have shown that solitary hamsters run significantly more when a wheel is available, but it has remained unclear how these factors play out when multiple hamsters share the same space, where competition and social dynamics might change the rules.

A team of researchers set out to solve this puzzle by observing five female golden hamsters living together under four different conditions. They placed the group into two types of cages: a large one measuring 580 by 392 by 400 millimeters, and a smaller one measuring 368 by 222 by 262 millimeters. For each cage size, they tested two scenarios: one where a running wheel was present and one where it was absent. This created a complete set of four environments to compare. To track the animals without disturbing them, the researchers installed an infrared camera directly above each cage, recording the hamsters' movements for a full twenty-four hours. Because the hamsters looked very similar, the team selected five individuals with distinct coat patterns—some with spots, some black, some white—to make it possible to tell them apart on video. They also attached a small black marker to the running wheel so they could count exactly how many times it turned.

The researchers then analyzed the footage to measure exactly how far each hamster traveled. They calculated the distance covered on the cage floor by tracking the movement of each animal's head from frame to frame, and they calculated the distance run on the wheel by counting the rotations of the marked wheel and multiplying by its circumference. The results offered a clear picture of how the environment shaped behavior. When a running wheel was available, the hamsters spent a significant amount of their active time on it, covering far more distance than they did walking on the floor. This confirmed that even in a group setting, the wheel remains a primary source of exercise. In fact, the presence of the wheel was the most powerful factor influencing activity levels; hamsters with access to a wheel moved significantly more than those without one, regardless of the cage size.

However, the size of the cage produced a more complex and surprising result. In the smaller cages equipped with a wheel, the hamsters ran significantly more than they did in the larger cages with a wheel. The researchers suggest that the confined space may have driven the hamsters to rely heavily on the wheel as a way to cope with the lack of room, essentially overcompensating for the restriction by running more intensely. In contrast, when the wheel was removed, the hamsters in the larger cages walked farther on the floor than those in the small cages, indicating that they used the extra space to explore. This suggests that while a larger cage encourages walking, a small cage combined with a wheel encourages running, and the wheel itself is the key driver of total activity.

The study also highlighted the social challenges of group housing. The data showed a wide variation in how much each individual hamster moved, with some traveling much farther than others. Video review revealed that multiple hamsters often tried to use the single running wheel at the same time, leading to competition. This suggests that in a group, access to exercise equipment is not always equal; dominant individuals may monopolize the resource, leaving others with less opportunity to move. While the study did not formally rank the social hierarchy of the group, the observation of these conflicts points to a limitation of the current setup. The researchers propose that providing multiple wheels might help balance the activity levels among the group members.

Ultimately, the findings indicate that providing a running wheel is essential for the physical activity of group-housed hamsters, particularly when they are kept in smaller spaces. The wheel serves as a vital outlet for their energy, allowing them to travel distances that would be impossible in a confined cage without it. While a larger cage offers more room for walking, it does not automatically lead to higher overall activity if a wheel is missing. The researchers conclude that the wheel is especially important in smaller enclosures, acting as a crucial tool to facilitate exercise. However, they caution that high activity levels do not necessarily mean the animals are happy; the intense running in small spaces could also be a sign of stress or frustration. Future work will need to look deeper into the social dynamics and emotional states of these animals to understand whether the increased movement is a sign of well-being or a reaction to the constraints of their shared home.