Shawn Achor helps people apply positive psychology to be happier and more effective at work. His latest line of enquiry: why can some people make positive change, and others can’t? We asked him to tell us more.

Musician Bernie Krause has worked with Stevie Wonder and The Byrds. But for the past 45 years, he's turned his attention to the birds, recording natural soundscapes. He tells his story at TEDGlobal 2013. Photo: James Duncan Davidson

At TEDGlobal 2013, Bernie Krause shared the saddest sound he’s ever heard in the animal kingdom. Here, he reveals the happiest.