What is pain?
The International Association for the Study of Pain (IASP) defines pain as an unpleasant sensory and emotional experience associated with actual or potential tissue damage.
The IASP also includes under this definition an important note: the inability to communicate in no way negates the possibility that an individual is experiencing pain and is in need of appropriate painrelieving treatment.
This is a very important statement that gives credibility to pain experienced by non-verbal populations of species, including all animal species. We are not yet fully capable of recognising when a bird is affected by pain, so it may be best to err on the side of over-estimation and assume that conditions that would be painful to humans are also painful to poultry.