Birds, unlike mamals like us, have the ability to regenerate their ear hair cells. That means that even if they "went deaf" from listening to headphones too loud or going to one too many rock concerts, they can grow back the damaged hair cells and regenerate their hearing!
Didn't click the link, but there is active research in ear hair cell regeneration in hopes of being able to learn why they can do it and why we can't, so that maybe, some day, humans with hearing loss can regain their hearing though therapies.
Edit:
Ok, so I got curious and actually skimmed the paper...They didn't make the 18 leghorn roosters that were between 12-15 weeks old deaf for the sake of making them deaf to study any crowing or behavior.
The premise of the study was to better elucidate the mechanisms of avian hair cell growth in response to damage. A sound is sent into the ear and the resulting electrical signal is recorded. Why is an electrical signal recorded? It is because to hear, mechanical waves are turned into an electrical signal that can be sent to our brains for processing. By sending in various frequencies, different portions of the ear (cochlea) are stimulated, and thus different electrical signals will be generated by the depolarization of ear hair cells and in the study, instead of being sent to the brain, it was recorded by the researchers for them to work their magic on in understanding what is going on.
So the paper was about hearing research to understand hair cell regeneration.
