hrm - wrong? Im never wrong.
assumptions :
Number :

(4+20) birds or (2*4)+20 birds? So 48 or 28 since you killed 1/7th i assume the number is divisible by 7 without remainder and the number of birds is 28.
The dead ones aren't going anywhere so you killed 4.
The live ones aren't gonna stick around to get shot again, so they dont remain.
but does a dead blackbird count as a blackbird or just a generic bird corpse?
anyway - I say 4 remain, but I still agree with LS_Boreas