In the context of Forgotten Songs, explain the Bird songs of the Installation.
Recordings are played of the songs of fifty bird species which used to live in the central Sydney area on two audio tracks - day birds and night birds - with "a calendared sequence of triggers that progressively allows for longer days in summer and longer nights in winter". Some of these birds songs can still be heard on the city margins but not in central Sydney. Based on investigations of doctor Richard Major in regards to the city soil types and examining Australian Museum collection of bird skins, a list of 50 species of both diurnal and nocturnal birds was provided. Consequently, the sound files of  those 50 species were gathered by the wildlife recordist, Fred van Gessel.
nocturnal Australian Museum Australia Sydney diurnal