The Sacramento National Wildlife Refuge Complex is part of the United States system of National Wildlife Refuges (NWR). It is located in northern California, in the valley of the Sacramento River.
The Sacramento NWR Complex was created in an attempt to resolve the conflict between the needs of migrating birds using the Pacific Flyway, and those of agriculture.
Bird ringing (UK) or bird banding (US) is the attachment of a small, individually numbered metal or plastic tag to the leg or wing of a wild bird to enable individual identification. This helps in keeping track of the movements of the bird and its life history. It is common to take measurements and examine the conditions of feather moult, subcutaneous fat, age indications and sex during capture for ringing. The subsequent recapture, recovery, or observation of the bird can provide information on migration, longevity, mortality, population, territoriality, feeding behaviour, and other aspects that are studied by ornithologists. Other methods of marking birds may also be used to allow for field based identification that does not require capture.