A fool chasing home counties bird (7)
I believe the answer is:
seagull
'bird' is the definition.
(seagull is a kind of bird)
'a fool chasing home counties' is the wordplay.
'fool' becomes 'gull' (synonyms).
'chasing' says to put letters next to each other (some letters chase after others).
'home counties' becomes 'se' (Home Counties in the South East of England).
'a'+'gull'='agull'
'agull' after 'se' is 'SEAGULL'.
(Other definitions for seagull that I've seen before include "Bird paradoxically fond of landfill sites" , "Avian scavenger" , "One sitting atop mast perhaps" , "Main creature" , "Marine bird" .)