Sources
http://www.telegraph.co.uk/earth/wildlife/5983953/Aesops-fable-is-true-shows-crow-study.html
http://news.nationalgeographic.com/news/2002/08/0808_020808_crow.html
http://www.edutube.org/en/video/intelligent-crows-crack-open-nuts-using-traffic
http://www.pbs.org/wnet/nature/episodes/a-murder-of-crows/full-episode/5977/
http://news.nationalgeographic.com/news/2006/06/060606-crows.html
http://www.nytimes.com/2008/08/26/science/26crow.html
Picture
http://news.nationalgeographic.com/news/2002/08/0808_020808_crow.html
http://www.edutube.org/en/video/intelligent-crows-crack-open-nuts-using-traffic
http://www.pbs.org/wnet/nature/episodes/a-murder-of-crows/full-episode/5977/
http://news.nationalgeographic.com/news/2006/06/060606-crows.html
http://www.nytimes.com/2008/08/26/science/26crow.html
Picture