A 'further reading' is not a reference; 'further reading' means 'here are additional sources you might find relevant about material not covered here'. Which of

A 'further reading' is not a reference; 'further reading' means 'here are additional sources you might find relevant about material not covered here'. Which of 'Triumph of the City', 'The Ghost Map', and 'Guns, Germs, and Steel' did the stuff about animals come from, if you hadn't already read them? That's right - you don't know! Because he's not giving a reference.