I have not had a chicken with these symptoms before but my cat has done this. I came home and noticed both of her water bowls were empty, one is a 1 gallon automatic waterer that had been filled that day. I refilled them and she wouldn't stop drinking. I rushed her to the vet who told me that excessive thirst is a sign of infection. After $1100 + , antibiotics, and a very invasive surgery, she is now the healthiest and most expensive free cat around.