I have ducks and chickens, and have noticed that they don't mind loud noises much. First off, we have the incessant crowing of the rooster. If he crowed a few inches from my ears, it would hurt and I would get reduced hearing if it happened a lot. But the hens never seem to mind in the slightest. I've also noticed that they don't bat an eye in the proximity of loud human activities, such as hammering or working certain machinery. I also read a story once about a farmer who stood on his scap heap and shot rats, with his chickens happily foraging by his feet. Has there been any research about this? Or maybe you have personal anecdotes to share?