supernumerary

ylimääräinen henkilö

statisti

tarpeeton A civil designation for somebody who works in a group, association or public office, without forming part of the regular staff; those distinguished from numerary. (For example, supernumerary judges are those who help the regular judges when there is a surplus amount of work.)
An extra or walk-on in a film or play; spear-carrier.
An animal which has not formed a pair bond and is therefore single.
1992, Sarah Anne Sloane, Supernumeraries at bushtit (Psaltriparus minimus) nests (page 50)
2004, Walter D. Koenig, Janis L. Dickinson, Ecology and Evolution of Cooperative Breeding in Birds, Cambridge University Press (ISBN 9780521530996), page 88

There are differences in the composition of the social group such as whether one or more sex provides help, and the stability of the associations between supernumeraries and the dominant breeders.

The best evidence so far that social supernumeraries are physically capable of bettering their lot concerns not rodents but birds.

Over close-ups of little faces with hare lips, little trunks with stumps instead of legs and arms, little hands with clusters of supernumerary fingers, little bodies adorned with a double row of nipples, we hear the voice of the Narrator.