Per the guys from Double Bull; anything with 4 legs does not like to see black spots where there should not be any. In other words, if a deer/elk/hog/coyote/antelope comes near your blind and all they see is camo, or to them "a big pile of sticks and leaves", no problem in their world. If they see this same pile with a large black opening in the middle, problem!!!

Just like Roskoe said, it is not necessary for turkey. There were several times this past spring where I was very close to birds while in my blind and they seemed to care less about the large black opening.

Hope this helps.