Do you Hear What I Hear? All about Chicken Hearing
Chickens hear very much like human beings do. They have two ears, one on either side of their head. They have eardrums, and an outer ear, middle ear and inner ear, just like we do. They are able to harness sound waves and send them to the inner ear.
Chicken ears aren't readily visible since they are covered by feathers. However, the ear lobes can usually be easily located. It's a myth that the color of a hen's earlobe dictates egg color, although many chicken breeds with white ear lobes do lay white eggs, and many with reddish-brown earlobes lay brown eggs. However, blue egg-laying Ameraucanas do not have blue earlobes!
Unlike humans, who tend to experience hearing loss as they age, chickens are able to regrow damaged hearing cells, so their hearing remains top-notch throughout their life. This is important since they are low on the food chain, so any advance notice of a predator's presence is critical. And in fact, chickens can tell how far away a sound is coming from, by gauging how long it takes that sound to reach each ear.
Baby chicks are able to hear their mother hen clucking to them while they are still in the shell. An embryo can actually hear by around day 12 of the incubation period. And once hatched, a baby chick will respond to their mother tapping the ground when she finds seeds or bugs. If you tap your finger near their feed, chicks in the brooder will hurry to investigate.
In my personal experience, I have found that chickens aren't generally bothered by loud noises. Fireworks don't faze them, and I was building their new coop a few years ago and using power tools right in their run and they barely blinked an eye. However, flap a tarp around them or over their heads and they panic. My theory is that loud noises generally pose no threat to a flock, while flapping from above could clearly signal the arrival of a hawk, owl or eagle.
It seems that chickens enjoy listening to classical music in fact. Some studies have been done which have led some commercial farms to start playing classical music, believing that it calms their flocks leading to fewer behavioral issues and more (and larger) eggs. Go figure. So crank up that Mozart and start collecting those eggs!