aberrant

Etymology

From Latin aberrāns, present active participle of aberrō (“go astray; err”), from ab (“from”) + errō (“to wander”). See aberr.

adj

1. Differing from the norm.
2. (sometimes figurative) Straying from the right way; deviating from morality or truth.
3. (botany, zoology) Deviating from the ordinary or natural type; exceptional; abnormal.
   The more aberrant any form is, the greater must have been the number of connecting forms which, on my theory, have been exterminated. 1859, Charles Darwin, On the Origin of the Species

noun

1. A person or object that deviates from the rest of a group.
2. (biology) A group, individual, or structure that deviates from the usual or natural type, especially with an atypical chromosome number.
   Also I think other birders realise you are struggling a bit when you start talking about aberrants[.] 1980, Bill Oddie, Bill Oddie's Little Black Bird Book, page 87