It should never be so tight as to cause swelling in your birds leg. Closed bands usually signify that a bird is captive-bred. Closed bands are the most reliable band which cannot be substituted unless cut-off. Open leg bands are found on legally imported wild-caught birds. They are open to allow fitting on a fully grown bird.
Some breeders use open leg bands on their aviary birds that are caught at adult size.
Bands come in metal or plastic. The colored plastic bands are usually used by breeders of captive-bred birds to differentiate between the males, females and parentage. Leg bands are an inexpensive way to identify your bird. The other alternative is microchipping. We feel that leg bands are important because they provide important identifications such as proof of ownership in cases of loss or theft, tracking and breeding histories, as well as they are required by government regulation.