Last updated April 17, 2018 at 11:09 am
How do you give a chicken hope? Show it a square of grey-coloured laminated card.
Colours associated with rewards have lasting effects on the mood of chickens. That’s the curious result of a Swedish experiment designed to measure optimism in the birds – a key indicator for whether they are coping with the stresses inherent in living in an enclosure.
A team led ethologist Hanne Løvlien from Sweden’s Linköping University used 96 Bovans Robust chicks raised from hatch. The birds were divided into groups, and cared for in pens.
Some groups lived in enclosures containing food and water along with a range of avian distractions, including wood blocks, perches and a secluded, sheltered area.
The others had food and water, but no additional facilities.
As they grew, all the birds were taught the difference between nine-centimetre-square laminated cards, coloured black or white. With each group one of the colours was associated with a reward of mealworms, while the other was not.
Some birds, the researchers note in a paper in the journal Scientific Advances, needed as few as nine repeats before they learned to associate either the black and white cards with reward. Others needed up to 89 attempts, and nine never quite managed to make the connection.
Once the chickens had been fully trained, the groups were exposed to a battery of stress tests (none harsh enough to cause lasting damage, if should be noted). These included dropping the temperature in the enclosures, pumping out heavy metal music and random sounds for 15 minutes a time, and varying the light levels.
Before and after the stress tests, the birds were shown grey cards – a tone intermediate between black and white.
Those birds that treated the card in the same manner as the reward card they had been trained to identify were deemed to be optimistic; those that ignored it were deemed to be rather glum.
To back up the behavioural evidence, Løvlien and colleagues also tested dopamine levels in the birds. Those exhibiting optimistic reactions to the grey cards were found to be carrying higher amounts.
The study found that the chickens living in the more complex environments were better able to deal with the effects of the stressors.
“If a chicken can hide under something or fly up and perch somewhere, it can manage a stressful situation better,” says co-author Josefina Zidar.
“We believe that the possibility of controlling the situation better resulted in these individuals being able to maintain optimism, even after a period with increased stress.”
The researchers also noted, however, that before the stress tests were conducted there was no difference in optimism levels between the chickens in the complex or simple enclosures.