Humphrey–Parkes terminology

The Humphrey–Parkes terminology is a system of nomenclature used to describe the plumage of birds. Before this system was developed, bird feathers were named based on whether people thought they were used for breeding or not, which often led to mistakes. The Humphrey–Parkes system was created to fix these problems. It is named after P. S. Humphrey and K. C. Parkes.

Under this system, the main adult plumage of a bird, especially when it comes from a full change of feathers called a molt, is called basic plumage. In many birds, the feathers they wear when they are not breeding are considered basic plumage. For birds that change their feathers only once a year, their one and only set of adult feathers is also called basic plumage.

Some birds go through a smaller change of feathers, called a partial molt, before they breed. These special feathers are known as alternate plumage and were often called breeding plumage in the old system. If a bird has a third kind of plumage besides basic and alternate, it is called supplemental plumage. This is most common in ptarmigans. The first set of feathers a baby bird has is called juvenal or juvenile plumage.

While a bird is changing its feathers, the process is called a molt. Depending on which kind of plumage will follow, the molt can be called a prejuvenal, prebasic, prealternate, or presupplemental molt. For birds that do not become fully grown adults right away, numbers are used to show which set of feathers they are wearing. For example, the first time a bird gets its basic plumage, it is called first basic plumage. These numbers are stopped once the bird reaches its full adult feathers.