They sacrifice something - an abundant summer acorn - today to get something better - a scarce winter acorn - in the future. It's a clear counter example to the claim above.

Except they don't mean to do anything. They're carrying an acorn, they pass a juicy spot, they feel compelled to stick the acorn in the spot. At no time does the squirrel think "I'll sacrifice this food now for food later!" So it's not reasonable to call it a sacrifice except metaphorically?

How on earth do you know that?

And what difference does 'knowing' make? Do they make the sacrifice or not? They clearly do.

By reading, being educated. Its far to late to be mystified about how animals work. Its a couple of centuries of study by now, about their instincts and behaviors.

And recall, 'understanding the concept of sacrifice' was the topic.

So you know how animals work! Excellent. Please build me a machine that does the same, to demonstrate your understanding.

It can be slow and inefficient to make up for lack of equivalent materials and mechanisms. A simulated one will do.

Or just explain how it works. I've been looking forward to reading that book. You'd sell some copies.

Also, a nitpick: it's a few millennia of studies by now. For example you can read Aristotle on the topic from 1700+ years ago.

As it happens, not only do they remember, they actually organize their nut storage in geographic chunks: https://www.scientificamerican.com/article/squirrels-can-sto...