you say flies i said add a word to make a bird,
storm PETREL- house MARTIN-marsh HARRIER- horn BILL
nice grid

Good spot- give yourself a point anyway. I tend not to have a different missing word each time but it could easily be a group- not intentional! I probably subconsciously chose those particular flies to be red herrings for the bird group. Horn was a false lead to trotter, house was a false lead to tv surnames, storm/ monsoon, but also sound like birds. A bit too much, though!