A beaver dam is probably the most famous example of an extended phenotype in nature, though on the sexual side one could mention the bowerbird’s bowers. Here’s a video of beavers working on their ‘lodge’ or home, which is situated in the middle of the lake created by the dam. It was sent in by Matthew Cobb with the comment, “Annoying commentary and music, but still great. And he was clearly very happy to have seen them at such close quarters.”
I didn’t find the commentary so grating, but what amazed me was when the stick-toting beaver went bipedal at about 1:58 in.
By the way, those of you who went to the Dawkins event here, or read my commentary, know that Richard considers The Extended Phenotype as his greatest book, and the literary accomplishment he’s proudest of. You can buy it for only $12.74 at Amazon, and the readers’ ratings are very high. I recommend it as your next biology book.
And look at the cover: