I must've downed 4 or 5 injured survivors with crows and didn't get the challenge. I even farmed one match and got 7 or 8 downs to be sure but nothing happened.
You need to only injure Survivors with the Dire Crows; after that, they can be downed by any means, and will count toward the challenge.
ive experienced the same thing just now.
I was trying this challenge and noticed that if I M1 a survivor right after they got damaged by birds it progressed the challenge. Did it 2 more times and completed it.
The challenge clearly states, you must down the survivors that were injured by Dire Crows, not down survivors with Dire Crows.