The leg ring on this Lavender waxbill records information about its origins
Rings are a legal requirement in some countries. In other countries, such as The UK, leg rings are not a legal requirement but it is still standard practice to fit them. Many breeders will choose to fit blank, colored plastic tags on the bird. These tags are used to help breeders track the family lineages in their aviaries.
Leg rings should only ever be fit by breeders who know exactly what they’re doing. When choosing a bird, be sure to check if their leg ring is sufficiently loose, it should be able to rotate around the bird's leg with ease.