That'll be In Drefia where there's 13 of them quite close to each other.
On rapid resp I was killing 250 of them every 30 minutes. So it's quite fast to finish in 2 hours. Since it's circular, you can just rotate on the spawns below - you may also want to every now and then throw a fire bomb at the fenced animals spawn marked with green (3 black sheep, 2 rabbits, 2 flamingos, among others).