There are a lot of documentaries freely available on YouTube.
Sometimes the producers release them for free, but most often other people upload the films and the copyright owners don't bother with taking them down.
xDocumentaries is a central place where you can easily find these documentaries...
A 2009 documentary that explores and questions dolphin hunting practices in Japan, especially the annual dolphin capture and slaughter in a cove in the Japanese fishing town of Taiji. It follows Ric O'Barry and people from the Oceanic Preservation Society as they conduct a covert operation...(show more)
A 2005 French feature-length nature documentary directed and co-written by Luc Jacquet, and co-produced by Bonne Pioche and the National Geographic Society. The documentary depicts the yearly journey of the emperor penguins of Antarctica. In autumn, all the penguins of breeding age (five years...(show more)