I've lost birds when I was 75 feet away using a weed whacker, making a ton of noise etc. I walked by the coop and found a pile of feathers where one of my guineas had been. I've switched from free ranging to a fenced in yard with an electric net fence. I let the birds out when I get home from work until sunset. So they get 3 hours of yard time. This was the compromise I had to make to keep them safe. I started this spring with 18 ducks, 20 chickens and 10 guineas, and lost 10 ducks, 1 chicken and 5 guineas, so I had to do something drastic or I'd have nothing left. The ducks and guineas would roam all over. so they took the hardest hit. The chickens stayed close to the coop, and benefited from their cautiousness.