The type of feathers located closest to the body of the bird is down feathers. These soft and fluffy feathers serve as insulation, helping to keep the bird warm by trapping air close to its body. Down feathers have a unique structure that allows them to be lightweight and provide excellent thermal insulation, which is essential for birds to maintain their body temperature, especially in colder environments.
In contrast, primary feathers are the long flight feathers found on the outer part of the wings, secondary feathers are located along the inner wing and also contribute to flight, and tail feathers, or rectrices, are found at the end of the bird’s body and are important for steering during flight. While all these feathers have critical roles, down feathers are specifically designed for insulation and are situated closest to the skin, making them essential for a bird's warmth and overall health.