Growing up on a cattle ranch, we had pet crows and pet ravens, both very intelligent.
But unless a human does as suggested and shows the crow or raven a few times, the odds of the bird figuring it out without human intervention are slim.
Both crows and ravens we had used tools to get things they wanted, sticks with a hook on one end to get inside a bottle to retrieve a seed or nut for example.
We didn't teach them that, they figured it out on their own, so, maybe one would wonder about that slot........I guess it's possible they could learn all on their own.