Is nest building learned or biological?

If a rat or a mouse were given no substrate (this is hypothetical, I'm not actually doing this) and left in a plastic tub, then gave birth, incapable of making a nest, and you were to do this for a few generations, would the future generations still try and form nests if given substrate or would it be bred out of them?

Good question, I'd guess that it would take more than just a few generations to remove something so ingrained into their mentality.

But the question is more is it ingrained in their mentality, or is it ingrained in their biology? Do they have some kind of instinctual need to build a nest, instinct would require selective breeding, not just exposure to the situation. But if it isnt something so base then perhaps a few generations of random breeding of rats who have not been exposed to nests should be adequate, but if it's biological a whole hundred generations could go by and they would go right back to it when given the chance.

I would vote instinct. There is no "nest" still around by the time the babies have their eyes open, but first time mothers always do it.

Instinct, but I think good mothering is a combination of instinct and learned behavior. I've had mothers which were completely clueless about raising their young if they weren't exposed to another mother rearing her young.

Depends on what you consider a nest. Some of mine don't really build a nest they just pile the babies on top of the bedding and the babies kind of make a hole in it.