There are two "Discovering Music" programmes on Mahler coming up on BBC Radio 3 this Sunday May 2nd (17:00 UK time) and the following Sunday, presented by Stephen Johnson. Here is the info:
"Gustav Mahler frequently incorporated singers into the line ups of his Symphonies, but he also used elements from his own songs in them. In the first of two programmes, in a year that sees the 150th anniversary of the composer's birth, Stephen Johnson delves into the world of Mahler's Symphonies to explore these echoes."
See here:
http://www.bbc.co.uk/programmes/b00s6sd6I think these programmes should be available to listen to after the broadcast via the BBC iPlayer.