Weight measurement of Greater One-horned Rhinoceros mother and calf

"Gopon," the mother of Greater One-horned Rhinoceros, and "Dekopon," her child who will turn two in September of this year (2026).

This time, we'll introduce the latest growth of the two animals being kept at Tama Zoo, as well as the ingenious methods that the zookeepers are constantly experimenting with to measure their weight.

According to literature, the standard weight for Greater One-horned Rhinoceros at around two years old is approximately 900-1,200 kg, and after this period, weight gain slows down. Dekopon also weighed 908 kg in July, indicating that he is growing well.

As mentioned in a previous article, the measuring board we had been using for Gopon was too small for him, and we were unable to measure his weight. However, thanks to the supporter funds we received this year, we were able to purchase a new measuring board. The new board is sturdy, large, and thick, making it possible to measure Gopon's weight. Gopon's weight in July was 2,151 kg.

Measurements are taken in the morning and evening when the mother and calf enter and exit the enclosure. A scale is placed in the passageway between the exercise area and the sleeping area, and the rhinos are made to stop one at a time on the scale. However, there are two rhinos, a growing calf and a large mother. Even if one of them steps onto the scale, the other will push it away when it arrives later, or it will try to hurry past in order to go to the exercise area. It was not easy. We have come up with various methods to get them to stop properly on the scale.

The passageway is narrow, so the two dogs cannot pass through at the same time. Therefore, the order in which they were allowed to pass through became important. Thanks to previous training, the mother, Gopon, can be guided to some extent by the handler's commands.

First, I tried to guide Dekopon while Gopon waited in the bedroom, but it failed when it ran off to the playground at the end of the corridor before the measurement was completed. Also, Gopon seemed interested in its sibling and sometimes pushed Dekopon from behind towards the playground.

So next, we switched the order and guided Gopon into the aisle first, having him wait with his body blocking the exit beyond the scale, and then guided Dekopon in after him. This worked, and even when Dekopon tried to move forward, his mother's wall was in front of him. Because it was a dead end, he stayed on the scale longer, and we were able to get a more accurate measurement.

However, this method presented a new problem. When Gopon, weighing over 2 tons, passed by first, his massive size and power caused the board and scale to shift, making it impossible to accurately measure Dekopon's weight when he stepped on it later.

To solve this problem, we modified the board. We added a frame that fits the scale and thickened the four corners of the board with wooden blocks to prevent it from bouncing up. As a result, it no longer shifts even when Gopon passes over it forcefully, and now we can measure both of them stably.

We will continue to implement various measures and carefully monitor the health and growth of both parents and children.

[Tama Zoo]

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