Field Trip Committee. With its great diversity of habitats, Washington state supports a great diversity of breeding bird species. A transect from the lowlands of western Washington across the Cascades and down into the Columbia Basin takes one through a series of life zones and habitat types, each of which has its own characteristic species. By this time of year, breeding is over for the most part, and most individuals of migrant species have moved away from their breeding territories.
Some late breeders are still around, as are the immature birds of most species.
In addition, migration from the north has begun, so most of the Washington breeding species are still present in the state, some albeit in reduced numbers, and many additional species are pouring into the state. This is a time of interest to students of bird plumages, as most adults are in molt, and many immatures are to be seen, in juvenal or first-basic plumages or molting between them. Species that breed in rich habitats tend to undergo molt before they migrate, while those in drier, less productive habitats where food resources have dwindled greatly may migrate quickly and then molt after they arrive in more productive habitats farther south. Habitat type exerts a strong selective pressure on molt, and different species of the same genus may have different molt strategies. Freshwater birds are not especially diverse in western Washington, where natural water bodies were historically not very productive of aquatic life.