The journey of weighing Rhesus Monkey: The measurement process

In the previous article, "The Journey of Weighing Rhesus Rhesus Monkey: Preparation," we described the process of weighing an elderly female macaque named "Shimobukure" and the preparation and creation of the necessary equipment. In this latest article, "Measurement," we will discuss the results of the weight measurement and how that data is being used for animal husbandry management.

We started this initiative in November 2024, and after about four months of getting Shimobukure used to the feeding station, we began recording Shimobukure's weight in March 2025. After various trials to ensure that he would definitely go into the feeding station, we decided to sprinkle puppy milk on his favorite bread to make it more appealing to him.

However, weighing him didn't go smoothly. Shimobukure was wary of the 3cm gap created by placing the scale, which hadn't been there during the acclimatization period, and he was reluctant to get on the platform.

As an improvement, we attached a 2.5 cm thick board around the weighing scale to minimize any gaps.

After these improvements, when we weighed the birds, they began to climb onto the feeding platform without hesitation, and we were finally able to weigh them reliably.

The graph above shows records of weight measurements taken every two weeks starting in March 2025. Based on these results, we consulted with a veterinarian about Shimobukure's weight management. During the summer, when animals tend to lose weight, we aimed to keep his weight stable at around 4 kg to match the decrease, and during the winter, when temperatures drop, we aimed to keep his weight stable at around 4.5 kg to maintain his body temperature.

Since we started this initiative, we've noticed changes in Shimobukure's behavior. Previously, he often spent time somewhat separated from the group, but now he frequently climbs to the top of the platform and settles down to rest within the group.

Furthermore, I feel that his improved ability to eat properly has given him more energy and confidence. Previously, he would often wait to see what the other monkeys were doing at feeding time and come to eat later, but since this initiative, he has been able to come and eat with the other monkeys without waiting to see what they were doing. Maintaining a stable weight may be contributing to this change in behavior.

Based on this experience, we would like to work on being able to measure the weight of other individuals as well, so that we can manage the health of the entire group.

[Inokashira Park Zoo Animal Care and Exhibition Staff, Onodera]

(March 29, 2026)