Bird, unfamiliar sort I check on (7)
I believe the answer is:
ostrich
'bird' is the definition.
(ostrich is a kind of bird)
'unfamiliar sort i check on' is the wordplay.
'unfamiliar' is an anagram indicator.
'check' becomes 'ch' (I've seen this in other clues**).
'on' means one lot of letters go next to another.
'sort' anagrammed gives 'ostr'.
'ostr'+'i'+'ch'='OSTRICH'
(Other definitions for ostrich that I've seen before include "Runner" , "Emu-like bird" , "Largest living bird" , "Someone unprepared to face the facts" , "Largest non-flying bird" .)