A framework to understand the emotional lives of animals was revealed yesterday.

Animal choices can be assessed objectively as evidence of pessimistic or optimistic decision-making which indicates their long-term mood.

Mike Mendl and Liz Paul, from the University of Bristol, and Dr Oliver Burman, from the University of Lincoln, looked through papers by experts from Charles Darwin to Paul Ekman and Jaak Panksepp to create the framework which can be used in the field of animal welfare and neuroscience.

Mike Mendl, head of the Animal Welfare and Behaviour research group at Bristol University’s School of Clinical Veterinary Science, said: “Because we can measure animal choices objectively, we can use optimistic and pessimistic decision-making as an indicator of the animal’s emotional state which itself is much more difficult to assess.

“Recent studies by our group and others suggest that this may be a valuable new approach in a variety of animal species.

“Public interest in animal welfare remains high, with widespread implications for the way in which animals are treated, used and included in society.

“We believe our approach could help us to better understand and assess an animal’s emotion.”

An animal living in a world where it is regularly threatened by predators will develop a negative emotion or mood, such as anxiety. Conversely, an environment with plenty of opportunities for survival resources creates a more positive mood state.

The researchers argued that these emotional states not only reflect the animal’s experiences, they also help it decide how to make choices, especially in ambiguous situations which could have good or bad outcomes.

An animal in a negative state will benefit from adopting a safety-first, pessimistic response to an ambiguous event, according to the review which is published online in the Proceedings of the Royal Society B.