Starlings flock.
Blackbirds though...I've started counting them as I drive down the road the last few days. Just ones on, or next to the road I usually count 30-50 along a 5k section and maybe 3-4 of any other species. So, let's see....That's an average of 40 per .05 square kilometers or 800 per square kilometer. Meaning 214,416,800 throughout NZ. All 215 million intent on eating any berries or fruit I grow. That counts as swarming! :an!gry