With warmer days becoming more frequent, it's time to start thinking about changing our wardrobes. In fact, it's not just humans who change their coats; other mammals also undergo a similar process. While the shedding of fur and subsequent growth of new fur in mammals is generally called "molting," many mammals living in regions with distinct seasons undergo a rapid transformation, changing from winter fur to summer fur and vice versa. It's just like changing our own clothes! Among them, Japanese Marten undergoes a particularly dramatic and striking transformation.

Japanese Marten is naturally distributed across Honshu, Shikoku, and Kyushu. While its fur color varies slightly depending on the region and individual, generally, in summer its head is black and its body is a dark orange to brownish color, while in winter its head is white and its body is a bright yellow.

Japanese Marten in its summer coat	Japanese Marten in winter coat

In illustrated books, Japanese Marten are depicted in their beautiful form after their molting is complete. However, at zoos, you can observe and follow the process of this transformation. We thought that by continuously sharing these daily changes, it might spark the discovery of previously unnoticed mysteries of living creatures, so we started posting on Twitter in the spring of 2022 using the hashtag "#MartenMorning".

Well, I started off with great enthusiasm, but since the shedding from winter coat to summer coat had already begun in April, the start of the new fiscal year, I had to rush to start taking photos. Furthermore, although I had planned to tweet every two weeks, when I actually started taking photos, the speed of the changes from late May to mid-June was much faster than I had imagined, and I was unable to closely track the changes.


Transformed in just two weeks
Based on this experience, we decided to increase the frequency of filming and post updates every 7 to 10 days in the fall so that we could closely follow the dramatic transformation from summer to winter coats. As a result, we were able to capture the molting process in order, starting with the head, face, entire body, and then the finer details around the eyes.


The way the color and amount of hair change little by little.
How exactly do Japanese Marten sense the seasons and molt? Recent studies conducted in captivity have shown that some individuals did not molt in environments with a constant light-dark cycle despite temperature changes, while molting was observed when they were moved to natural conditions with sunlight. It seems that they sense the seasons and molt not through temperature, but through changes in day length.

Our Japanese Japanese Marten are sure to show off another spectacular transformation this year. When you visit, be sure to compare them with the photos on tweets tagged with "#MartensChangingOutfits" and wonder, "What do they look like today? What will they look like in the future?"

Reference: Funakoshi, K., Nagasato, A., Takenouchi, S., Kannonji, R., Kikusui, M., Uchihara, A., and Tamai, K. 2017. Annual malting cycle and photoperiods that affect seasonal coat color changes in the Japanese marten (Martes melampus). Mammal study, 42: 1-10.

[Inokashira Park Zoo Zoo]

(March 9, 2023)