Roxen, especially the eastern parts, is very good for bird watching. There are nature preserves at Svartåmynningen (http://www.e.lst.se/miljo/skydd/naturreservat/sidor/064_sida1.html) and Kungsbro (http://www.e.lst.se/miljo/skydd/naturreservat/sidor/028_sida1.html).
See also the Roxen webserver.