The degree of optimism a chicken experiences in its day-to-day life depends on the complexity of its environment, new research has shown.
Many people might be surprised to learn that chickens experience optimism at all, and many more might be bemused to discover that in an extensive study conducted by scientists from Linköping University in Sweden the thing that most inspired hope in the birds was a small square of grey card.
In a paper published in the journal Scientific Reports, a team led by evolutionary biologist Hanne Løvlie set out to determine whether stressful conditions affected chickens’ emotional stability. To do this, the researchers used both behavioural and chemical measures.
Løvlie and her team raised a batch of female chickens (Gallus gallus domesticus) from the moment they emerged from eggs. The brood was divided first into two cohorts: one living in a physically plain environment, and the other in surroundings full of stimuli, such as varied floor coverings, multiple perches and secluded areas.
Both groups had unlimited and free access to food and water.
Once established, the training started. Each chicken was shown, repeatedly, squares of black and white card. Behind one was a reward, in the form of a tasty mealworm. Some birds were trained to associate food with white cards, others with black.
As a control, the researchers then measured the levels of dopamine – a neurotransmitter that correlates with stress – in all the chickens. They found no difference in stress levels between the plain-living cohort and those in the more complex environment.
All the birds were then exposed to environmental stressors, including changes in temperature, bursts of heavy metal music, random noises, and flashing lights. None of them were physically hurt.
Løvlie and colleagues then set about measuring the presence of optimism. They did this by showing them grey cards – a tone exactly midway between black and white. If a bird pecked at the card looking for a reward it was judged to be optimistic. If it ignored it, then that was taken to be an expression of pessimism.
Behavioural evidence was backed up by further dopamine tests.
The results showed that the chickens in the complex environment were much more likely to be optimistic than those in the simple one.
The researchers concluded that environmental complexity serves as a buffer against the negative effects of stress, and suggest that this should be taken into account when designing enclosures for farmed animals.
Andrew Masterson is a former editor of Cosmos.
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