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When we watch a bird we see its size, shape and feather patterns as well as its location and behaviors. All of this information helps us identify the bird. This week we are focusing on the external characteristics of the bird: its shape, its size, and its feather patterns.
When you observe a bird it is important to focus on features that will help you determine its identity. The bird's head provides some of the most important clues. Notice the shape of the bird's head, the color, size and shape of its bill, the location, color and size of its eyes, as well as the feather patterns on its face and head.
The bird's overall shape, its location in the environment and its flight patterns provide additional clues to its identity.
Molts and Plumages
A feather is a nonliving structure that can't be repaired if it becomes worn or broken. Birds regularly replace their feathers, a process known as molting. Birds can replace all of their feathers (a complete molt) or some of their feathers (a partial molt). An individual feather can be replaced if the entire feather is lost between molts. Damaged, broken or worn feathers are replaced during the next regular molt.
Producing new feathers requires a lot of energy so feather replacement usually occurs when the bird is not engaging in other energy demanding activities such as feeding young or migrating. During the molt birds are more vulnerable to predators and they may have more challenges getting food. Molting can occur before and/or after migration. Many North American birds molt in the late summer after the end of the breeding season and before the beginning of fall migration. Some birds exchange their colorful breeding plumage for a more subdued winter plumage. These birds have a complete molt and a partial molt each year.
Feathers
A bird's skin consists of two parts, the external epidermis and the internal dermis. New layers of skin cells develop in the dermis. As these dermal cells move toward the skin surface they lose water and flatten. Epidermal cells protect the dermis and prevent water loss.
Feathers are created in follicles in the epidermal layer. During the development of the feather a blood vessel from the dermal layer provides the nutrients. The feather develops in a thin feather sheath that breaks open to release the feather vanes when the feather is completely formed. The feather's blood supply is cut off when feather development ends. Growing feathers, known as pin feathers, can be seen sticking out of the surface of the skin.
Mature feathers are composed of the protein keratin, a metabolic product of the dying follicle cells. Keratin is also a component of scales and claws. Avian keratins have different amino acid sequences from keratins found in reptiles and mammals. The keratins in bird feathers are very difficult for animals to digest. Feather recycling in the environment may be done by bacteria and fungi.