Chickens go red in the face when they're flustered - just like humans, study finds

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Getting red in the face with rage might seem like a uniquely human trait.

But according to scientists in France, hens also turn a shade of rouge during 'negative situations of high arousal'. 

In a new study, chickens were either fed a delicious treat of mealworms or captured by one of the researchers while cameras recorded their faces.

While the chickens got a little red when they were happy, the scientists found that they got the most colour when they were flustered or agitated. 

Chickens have a lot of blood vessels close to the surface of the skin in their faces so the skin becomes bright red when blood flow increases. 

Researchers have found that chickens who are angry or scared (right) are much more red in the face than chickens who are calm (left)

The study was led by researchers at the French National Research Institute for Agriculture, Food and Environment (INRAE).

Delphine Soulet, one of the study authors at INRAE, told MailOnline: 'This finding may help, for example, to evaluate the quality of the human-animal relationship.' 

Reddening of the face during times of agitation has already been observed in a few other birds such as blue and yellow macaws.

To see if chickens had a similar response, the researchers at the French National Research Institute for Agriculture, Food and Environment (INRAE) observed six Sussex laying hens over a period of three weeks 

The birds were either fed a delicious treat of mealworms or were captured by the researchers and held with their wings covered for a minute. 

During this time the chickens were carefully recorded, gathering 18,000 different pictures of their faces.

Using a computer programme designed by the researchers, they were able to observe that the chickens got a lot more red-faced during periods of agitation. 

Ms Soulet says: 'In our study we found that hens blush in positive situations of high arousal associated with reward and pleasure.

'But the highest blushing was observed in negative situations of high arousal, for example, when we caught the hens.'

The chicken's faces were studied by a computer program which assessed the details of their faces (pictured) to see how they became more red during agitation 

It is not known exactly why chickens blush in this way, however, Ms Soulet suggests that it might have a 'signalling function' to show emotional states to other birds. 

Meanwhile a paler face is a sign of 'calm and contentment', because chickens who were resting had little redness until something agitated them. 

The researchers were also able to use this information to see how chickens got used to humans over time.

A group of 13 chickens were slowly acclimatised to humans over time while another 13 were left on their own.

The group that were acclimatised maintained a lighter skin colour, indicating a calmer state when the experimenter was nearby. 

These three pictures show a chicken in different states. The chicken's face is pale when calm (left), slightly more red when receiving a reward (middle), and much more red when being captured (right)

The researchers say this could be a test for the strength of the relationship between  humans and chickens, and show when chickens are more comfortable around people. 

Ms Soulet adds: 'More generally, these new facial markers of emotions could be used in other bird species maintained in captivity for conservation programs or as pets.'

In their paper, published in Applied Animal Behaviour Science, the researchers write that understanding bird's emotional or 'affective' states is key to 'comprehending their sentience'. 

However, assessing the extent to which animals like chickens feel emotions is extremely difficult.

The researchers say this technique use could be used to assess the welfare of captive chickens and to judge the quality of human-chicken relationships (file photo)

Ms Soulet explains: 'Defining the emotional ranges in humans is already a challenge with no real consensus so far.

'Even defining whether two human beings share similar emotional ranges is tricky and under cultural influence.'

It is believed that all vertebrates including birds have the same six basic emotions: fear, joy, anger, disgust, sadness and surprise. 

Previous research has also suggested that chickens may feel something like empathy, especially in hens whose chicks are being disturbed. 

Chickens also display a wide range of emotions in their clucks, which can easily be discerned by humans.  

Yet Ms Soulet says this does not necessarily mean that chickens feel emotions in the same way we do.

'We would rather say that they are able to, for example, feel fear-like or anger-like emotions,' Ms Soulet says.