Our hens are in a large free range yard and have free access to their laying ration. They forage for bugs most of the day. Problem is, hundreds of small birds from everywhere fly in and eat the chicken feed all day long. They are fat and numerous. Every evening I refill the feeder because the local birds clean it out. How can I deter them? Unfortunately the hens don't mind them all all until they are the size of crows, and just let anything smaller help themselves. Any ideas or designs I can try to deter the local wildlife? Feeding them all is expensive.