I’ve nothing empirical to back this up, but it’s my understanding that shiny objects like bottle caps are prized toys, and the sort of thing one might be gifted by corvids who have taken a liking to you. I have heard plenty of anecdotal evidence that crows will exchange gifts with one another, and with humans, to develop and nurture positive relationships.
Someone pondered a correlation between intelligence and some notion of “evil”. I personally believe empathy and altruism are highly connected to intelligence, and the act of giving a gift to another is suggestive of both attributes.
There are also examples of altruism in other species not frequently considered intelligent. Vampire bats will regurgitate food to share with others, even if they are not tied by familial bonds and even if there’s no other tangential benefit to the individual giving up its own nutrition. We have also recently observed female tigers caring for and protecting another female’s cubs while she feeds, which is novel behavior to observe in typically solitary tigers.