Tranquill is an avian Pokémon that resembles a pigeon.
Tranquill seem to have very strict requirements and a more serious nature than Pidove, and can rely on their keen intuition and sharp vision to pursue the route, looking for their targets. But Tranquill are also very friendly, so it is not necessary for human to question about their loyalty. Additionally, Tranquill seem to have a spirit of pacifism, which might be a reason why some humans believe that they live in a kingdom full of peace.
Tranquill's name seems to be the word tranquil, meaning peaceful, which is also similar to what the dove represents. It also contains the word quill, writing utensils made out of primary-feathers from birds.