12 June 2023

What do animals do? What do they think? Do they have feelings? These are questions that have fascinated people through the ages and represent a field of research of their own. In ethology, Linköping professor Per Jensen is one of the leading figures.

Per Jensen with a chicken in his hands.
Professor Per Jensen joined Linköping University in 2002, having previously been a professor at the Swedish University of Agricultural Sciences for several years. Charlotte Perhammar

We change out of our regular shoes, which are left on one end of a pine wood bench. At the other end, we put on loan boots. The risk of contamination must be minimised. On an inconspicuous grey door there is a small warning text designed to keep unauthorised persons out. Inside, there is a smell of wood shavings mixed with bird droppings and sunflower seeds. It is hot and humid.

Per Jensen is a professor at Linköping University who has devoted his professional life to trying to understand animals. He picks up one of the white, medium-sized and slightly shabby chickens and holds it gently in his hands. At first it is tense, but it soon relaxes.

“Chickens are the world’s most numerous pets and birds, in all categories. They’re often kept in highly industrialised environments and everything we do to the animals has an effect on them. My research will find out how the animals are affected and how they can be given the best life possible,” he says.

Ethology – studies of animal behaviour

Per Jensen has spent almost 40 years researching the animals we live closest to – dogs, pigs and chickens – and how their behaviour is affected by having lived close to people for a long time.

We are in the hatchery at Campus Valla where much of his research is carried out. Research that has attracted international attention and put animal welfare first. The hatchery is also one of the few places in the world that holds a breeding population of red junglefowl that are the origin of all domestic chickens.Portrait of Per Jensen.Per Jensen, professor of ethology at the Department of Physics, Chemistry and Biology at Linköping University. Photo credit Charlotte Perhammar

In three separate enclosures, or aviaries, about fifty chickens run around squawking, pecking and playing.

“When I started studying at university many years ago, we had a lot of lectures on the behaviour of exotic birds and strange fish that no one saw in real life. But there was really nothing about our pets, which are closest to us,” says Per Jensen.

His interest in animals began long before those first courses at Stockholm University in the mid-1970s.

“I’ve always loved animals and got interested in animal behaviour in upper secondary school and decided that ´this is what I want to devote my life to`,” says Per Jensen.


When he later graduated, he was the first in the Nordic region to do so in the ethology of domestic animals. At that time, it concerned pigs and their natural behaviour.

In large-scale production of fattening pigs, sows with piglets were previously fixed in stalls where they could not even turn around, and the piglets were often crushed to death.

A life far removed from how their wild boar relatives live in the wild. Per Jensen therefore studied the behaviour of pigs that are allowed to live in large natural enclosures all year round. It turned out that their behaviour was remarkably similar to that of the wild boar. This led him to what has been at the core of his research – domestication. In other words, what has happened to animals and their behaviour since humans took control of their breeding and thus changed their genetic makeup.

“Given how different domesticated animals look, not as much happens to their behaviour as you might think. A pig looks very different from a wild boar, but when you let them out into the forest, they behave exactly the same,” says Per Jensen.

He believes that the results were an eye-opener and gave a deeper insight into the actual needs of the pigs. It turned out that the same applies to domesticated chickens and to all domesticated animals.

Industrialised agriculture

Chickens are a good research object for studying domestication. They have been pets for over 8,000 years but still have a very strong urge to perch high off the ground when sleeping to avoid predators. This an instinct that is shared in the wild by their red junglefowl relatives. Yet, it is a need that is rarely met in increasingly industrialised agriculture.

When chickens do not get an outlet for their most basic needs, they become stressed. This in turn gives rise to various behavioural disorders such as feather pecking, cannibalism and other horrors. This type of phenomenon breaks out mainly in large industrial flocks. Internationally, a problem such as feather pecking is solved by amputating the upper beak of chickens. A method that is banned in Sweden. But when economic interests are strong, animal welfare often takes a back seat.Chicken held between two hands."Complex emotions such as jealousy, shame, empathy and sadness are also found in many mammals, and probably even birds", says Per Jensen. Photo credit Charlotte Perhammar

Yet Per Jensen believes that ethology research has made a difference for many animals because it has resulted in changes to legislation. Thanks to this, Sweden is in many ways a pioneer in animal welfare, where farming is moving more and more away from caged chickens, and pigs are no longer allowed to be kept fixed in stalls, for example.

The same emotions as us

The findings on how domesticated chickens and pigs function apply to all domesticated animals such as cows, sheep, goats, horses, geese and so on. And considering that all mammals, fish and birds share the same basic emotions as humans, research to understand them becomes increasingly relevant.

“Emotional experiences are very old mechanisms in purely evolutionary terms. But what research has shown in recent years is that even more complex emotions such as jealousy, shame, empathy and grief are also found in many mammals, and probably even birds,” says Per Jensen.

To the public, Per Jensen is best known for his work with dogs, where his interest stems from childhood and his first encounter with the wolf's domesticated relative. What makes dogs so interesting from an ethological perspective is that everything that can be said about domesticated animals applies to all of the different species – with the exception of dogs. They have changed a lot compared to their wolf ancestors. Their innermost core remains unchanged, but they have adapted a tremendous amount to living with people, which they are believed to have been doing for 20,000 years.

“A dog is closer to a human than to another dog. This has to do with the fact that they are our oldest pets and that they come from an extremely collaborative species that reminds us of humans, so they find it easy to adapt to us,” says Per Jensen.

Genetics and neurobiology

In recent years, the work has become increasingly interdisciplinary. Since domestication is a genetic process, researchers need to understand which genes are changed and expressed and how this affects behaviour.

A relatively new research area for Per Jensen is the neurobiology of domesticated animals. Here he examines how the brain is affected. Research has shown that brain size decreases in all domesticated animals, except for one part that grows instead – the cerebellum.

“That’s a big surprise! The cerebellum is considered to be the ugly cousin of the brain that allows you to control your movements and not much more than that. But it turns out that it is involved in a lot of cognitive processes such as learning and social understanding. Now we’re trying to understand why it grows,” says Per Jensen.

Shaping ethology

He puts the now sleeping chicken back into its aviary. It wakes up and quickly runs away and starts playing with its friends. We walk out through the inconspicuous door and change from boots to shoes and then go out into the sunshine at Campus Valla.

Per Jensen joined Linköping University in 2002, having previously been a professor at the Swedish University of Agricultural Sciences for several years. The big attraction of Linköping University was the opportunity to teach more, while at the same time being involved in building new educational programmes.

For 20 years, he has been involved in shaping undergraduates, doctoral students and an entire research field.

“Yes, maybe so. When I look around, I realise that I have been involved in teaching or supervising very many of the people who work in this area in Sweden. But above all, I’m happy if my research has led to us getting a little better animal husbandry and better knowledge about how animals function.”

Portrait of Per Jensen.“I’ve always loved animals and got interested in animal behaviour in upper secondary school and decided that ´this is what I want to devote my life to`,” says Per Jensen. Photo credit Charlotte Perhammar

Prize for animal welfare research

"It doesn’t get any bigger than that in this field".

In 2023, Per Jensen was awarded an international prize for his research in animal welfare. In the industry, the UFAW Medal for Outstanding Contributions to Animal Welfare Science is the highest award you can receive.

“I’m very happy to get this award. It doesn’t get any bigger than that in this field. Those who have previously received it are my role models and some of my most important colleagues around the world,” says Per Jensen.


Read more about Per Jensens' research

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