Name the bird Leo, nothing less! (5)
I believe the answer is:
title
'name' is the definition.
(I've seen this before)
'bird leo nothing less' is the wordplay.
'bird' becomes 'tit' (tit is a kind of bird).
'nothing' becomes 'O' (looks like zero - 0).
'less' indicates named letters should be taken away (less can mean minus).
'leo' with 'o' taken away is 'le'.
'tit'+'le'='TITLE'
'the' is the link.
(Other definitions for title that I've seen before include "Name signifying rank" , "Right - name - address" , "Name, honorific" , "Name - legal right" , "Distinctive name" .)