Look at those pictures. Shame on all who are involved in non-human research. These beings belong in the rain forest, not a plastic box inside a laboratory!
Imagine that if you'd have so much funding that you'd be able to cover a km2 in a forest with camera's and microphones, some remote controlled tools and enough food to experiment with. I think one could've made some kind of improvised tool that drops nuts when you handle a coin or something else. The only thing you then have to do is watch for a couple of interactions where one bird hands the other bird a bottle cap to exchange.
Just extend the above experiment with such tracking and I'd think you can reach the same conclusion as this article had, but then with farrrr more comfortable ethics?
https://www.youtube.com/watch?v=LJG3282QU4g
Just extend the above experiment with such tracking and I'd think you can reach the same conclusion as this article had, but then with farrrr more comfortable ethics?