Chickens and hens are not seen in-game, except in their roasted form, but a few references imply their existence.
Stated before, the dead chicken can be found on a roast.
Outside of St. Edgar's Church, two thugs are arguing, and one calls the other chicken. Somebody writes in a journal about being glad that Captain Moira died, and that if Ginny was too chicken to tell Edwina Moira, then he/she would.
Gamall will taunt Garrett, calling him a 'chick'.
In the famous heated argument in Life of the Party, a guard working for Lady Van Vernon yells to the Master Willey's archers to "...run and rescue your helpless limp lord, before he flounders in his own vomit, or wakes up naked in a hen-coop!"