There are different opinions about why Tadayoshi Okura is called roast bird.

One theory is that Tadayoshi Okura was chased by the enemy in the war. In order to escape the enemy's pursuit, he had to catch a wild bird and roast it to survive. This legend is widely spread and has become one of the representative symbols of Tadayoshi Okura.

another way of saying it is that Tadayoshi Okura is a member of Kansai Genese 8, a group of Japanese Genese office, and also a drummer in the group. During the Warring States Period in Japan, roasted bird was considered as a very precious food, and it needed to master certain cooking skills to make it. Tadayoshi Okura, as a military commander, often needs to find food to maintain his health in the process of marching and fighting. Therefore, he not only learned how to roast birds, but also often shared this delicious food with soldiers. Therefore, he may be called roast bird because of this historical origin.

The above are two possible reasons why Tadayoshi Okura is called roast bird, and the specific reasons may need further understanding and confirmation.