Question: even highly intelligent organisms like humans do not choose the food they want because it is better for them, so is the "choice" of the chicken reliable?

Louise Pendry answered on 17 Mar 2010:

Hey there!

You are one very smart cookie – that really is the billion dollar question! Lovin’ it.
This is gonna be a long reply – hope you are ready 🙂

You are dead right – the choices that an animal makes (even humans) are not always reliable. Scientists make lots of assumptions:
1) Animals will generally make reliable choices (sometimes called ‘rational’ choices or ‘optimal’ choices).
This is because of the evolution and survival of the fittest. If an animal kept making stupid decisions that risked its life or ability to reproduce then it would produce less offspring then smarter animals. If you are dead you cannot produce offspring. If you have no money (or shelter, food, etc) you cannot look after offspring so they all die too.
So ‘the unreliable-decision-making gene(s)’ (it’s a bit more complicated but it boils down to that really) don’t get passed on and die out/become very rare leaving only animals that make reliable choices. Unfortunately even ‘reliable choosing animals’ can screw up a choice though.
2) Animals are competent to make a choice in the situation they are tested in.
Interesting issue!
If the environment is not the environment the animal evolved in then is it able to choose wisely? Not necessarily! Also, how the animal feels at the time of testing can affect their ability to choose. In my work I found that the stress of being really hungry all the time made it hard for the birds to make a reliable choice.
3) Animals choose something because it makes them feel better.
Some scientists think animal welfare is just about how an animal feels. But other scientists think this is too simple. If a cat is hit by a car and is really badly injured (mangled body, loads of broken bones, cuts, etc) is its welfare good if I give it a painkiller so that it feels pain-free or is its welfare bad? If I choose to eat Mars Bars all day but am then too fat to walk so cannot go out with my friends is my welfare good or bad? I chose to eat the Mars Bars!

The great thing about scientists though is they investigate their assumptions.

One study I really like used layer-chickens. Layer chickens need loads of calcium in their food because they use so much calcium to produce eggs. If they don’t get enough calcium then they are very prone to get broken bones. Scientists used choice tests to find out whether chickens would prefer a diet with extra calcium when they had too little calcium in their bodies. They created two diets – one was normal chicken feed and the other diet normal feed plus loads of extra calcium. They found that when chickens needed extra calcium they picked the calcium-rich diet but this preference disappeared when chickens had plenty of calcium in their bodies already. So chickens can choose food wisely! And everyone thinks the chicken is a dumbass – how wrong is that??? 🙁

In my work I know (because of the work my bosses have carried out) that when I offer the birds a choice it is a choice between two ‘healthy’ diets. My bosses took two sets of birds – they fed one group of birds (called the control group) the chicken feed that birds normally get fed when on farms. They fed the other group (called the experimental group) a diet that contained appetite suppressants and fibre. They measured the birds and looked for differences in the health of the birds. They didn’t find any differences. Both diets scored well on signs of physical health. So, we know that the birds will be healthy regardless of what diet it chooses. What we don’t know is if it ‘feels better’ on one of the diets. You know yourself that hunger doesn’t feel nice. If you could choose between the two diets would you choose the diet that made you feel ‘good’ or feel ‘bad’? In this situation how confident would you be that your choice was reliable?

But, my chickens didn’t give me reliable choices. In my original experiment I offered them a choice between the two diets mentioned above. The birds showed no preference. So…..
I had to ask why?
Did they show no preference because….
A) They liked both diets equally?
B) They couldn’t tell the two diets apart?
C) They couldn’t associate the colours with the diets? (they had to associate different colour maze arms with different diets if they were to be able to choose properly – see my profile for info)
D) They were too hungry to learn?
And so I had to start investigating these assumptions. This is was science is like – every ‘result’ you get leads to loads more questions!