Maybe it doesn't make sense in the short term, looking at energy in-energy out, but perhaps a sense of fairness i.e. getting your "fair share" has long term evolutionary benefits for a social animal, i.e. those who've settled for second best have had less offspring overall. In a longer study, though, they might have caved if the cucumber was the only sustenance on offer.
I agree. I'm just pointing out that it really does highlight the idea of "fairness" with in their head.
Without fairness as a concept, it's simple: do task, get food.
With fairness are seeing what other animals are getting, expecting the same, not getting it and realizing that they are getting the short end of the stick