They are the only three US state abbreviations whose two letters are next to each other in the alphabet.

DE – Delaware
HI – Hawaii
MN – Minnesota

After shooting a quarter of the birds, the rest would fly off, so the remaining birds, brutally shot by you, would be:

(2 × (4 + 20)) / 4 = 12

It was a murder of crows.

It’s a palindrome (a word or phrase that’s spelled the same backwards and forwards).