One of my Icelandic hens illustrating use of colored, numbered bandettes for identification. Right band is blue (she is in the Blue clan), left band is yellow (she was hatched in 2013). The numbers are unique. That is, the number on the left is unique among all yellow bands; on the right, unique among all blue bands. Thus, even if one of the bands is lost, the remaining band positively identifies the hen, in this case Solveig.