Tackle first of errors in flier (4)
I believe the answer is:
kite
'flier' is the definition.
(kite is a kind of birdanimal)
'tackle first of errors' is the wordplay.
'tackle' becomes 'kit' (both can mean gear or equipment).
'first of errors' becomes 'e' (kst letter of 'errors').
'kit'+'e'='KITE'
'in' is the link.
(Other definitions for kite that I've seen before include "Bird of prey and flying toy" , "Flying toy or kind of hawk" , "High as a - -" , "It's flown in the wind at the end of a string" , "It flies with string attached" .)