Marian Dawkins at Oxford University has pioneered a number of studies that explore what animals prefer and how much they want it.
To do this she has designed experiments where animals must work for access to different choices.
Measurements of how hard the animal will work begin to tell us how valuable that resource is to the animal.
This provides a way of measuring the animal's strength of preference.
For example, animals can be trained to push against a door to open it to get access to one type of resource or another.
By putting heavier and heavier weights onto the doors you can find out how hard the animal is prepared to work to reach its choice.
Similarly you can make the animal do something it prefers not to.
Chickens do not like to squeeze through narrow spaces, but they will if this gives them access to something they really desire such as a place where they can dust bathe.