Defences of a large bird (6)
I believe the answer is:
alibis
'defences' is the definition.
(alibi is a kind of defence)
'a large bird' is the wordplay.
'large' becomes 'l'.
'bird' becomes 'ibis' (ibis is a kind of bird**).
'a'+'l'+'ibis'='ALIBIS'
'of' is the link.
(Other definitions for alibis that I've seen before include "Pleas of being elsewhere at the time of a crime" , "They're useful to have if accused of crimes" , "Defences of being elsewhere at times of crimes" , "Defences to charges - was elsewhere at the time" , "Defences - was elsewhere at time of crimes" .)