A new study in Proceedings of the Royal Society B says it is the first to demonstrate that birds possess empathy - and they say they have verified it using both behavioral and physiological methods to measure these traits.

Using non-invasive physiological monitoring, the researchers say domestic hens show a clear physiological and behavioral response to their chicks' distress.   During one of the controlled experiments, when the baby chicks were exposed to a puff of air, the hens' heart rate increased and eye temperature decreased. The hens also changed their behavior and reacted with increased alertness, decreased preening and increased vocalizations directed to their chicks.

Some of these responses have previously been used as indicators of an emotional response in animals. In domestic chickens, time spent standing alert is associated with higher levels of fear. Previous research carried out by the same group has shown that hens also selectively avoid surroundings associated with high levels of standing and low levels of preening.

Jo Edgar, Ph.D. student in the the University of Bristol's School of Veterinary Sciences, said, "The extent to which animals are affected by the distress of others is of high relevance to the welfare of farm and laboratory animals.  Our research has addressed the fundamental question of whether birds have the capacity to show empathic responses.

"We found that adult female birds possess at least one of the essential underpinning attributes of 'empathy'; the ability to be affected by, and share, the emotional state of another."

The researchers say they used chickens as a model species because, under commercial conditions, chickens will regularly encounter other chickens showing signs of pain or distress due to routine husbandry practices or because of the high levels of conditions such as bone fractures or leg disorders.