Aberrant
Abnormal or unusual. An aberrant individual is one which in some way is not typical of its species, for example one showing features of albinism. The Long-tailed Tit Aegithalos caudatus can be described as aberrant from the 'true' tits (family Paridae), so much so that it is placed in a separate family (Aegithalidae).From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver