American Bison molting and shedding its fluffy coat

Ueno Zoo keeps two American Bison. From spring to summer, you can see the changing seasons reflected in the two bison's bodies.

American Bison are animals that live in the vast grasslands of the prairies in North America. This region experiences extreme temperature fluctuations, with summer temperatures reaching 40°C and winter temperatures dropping to -20°C. Therefore, in winter they grow a thick, fluffy winter coat to protect themselves from the cold, and in summer they shed that coat to stay cool. This period of shedding and changing their fur is called the "molting season."

The two American Bison at Ueno Zoo also began molting around February, and it is currently at its peak. At first, the fur on their heads and legs was falling out in small flakes, but recently the fur on their backs has started falling out in large clumps, almost as if the skin is peeling off.

They can often be seen rubbing their bodies against the wooden fence in their enclosure or taking sand baths to shed old fur. Sometimes, clumps of fur will fall off while they are running around. The enclosure is littered with countless clumps of fur, making cleaning a real chore. Their unique mottled appearance, with some parts of their bodies covered in fur and others still intact, is something you only see at this time of year.

The winter coat, designed to withstand the cold, has a double-layered structure of long, stiff hairs and short, soft hairs that help retain body heat, but the texture differs significantly depending on the body part. The head and neck have stiff, curly hairs, while the back has fluffy hairs. The hair on the front legs has a significantly different texture from the rest of the body, consisting of long, stiff hairs growing in clumps.

These hairs not only protect against the cold but also shield the skin from the grass in the meadow, which is why they are said to be coarser than those on other parts of the body. Observing these differences in hair texture is unique to molting season and is one of the interesting discoveries to make.

It would have been great if the molting had been completed before the heat really set in, but judging from their slightly comical appearance with patchy fur remaining, it looks like it will take a little more time. The two bison are spending their days leisurely, taking measures to stay cool in the heat, such as using a spot cooler on hot days. Be sure to visit Ueno Zoo to observe American Bison in their molting season.

(Ueno Zoo East Garden Animal Care and Exhibition Staff)