Task: Question Answering
Input (English): Passage: In the years following his recuperation from the heart attack, Bowie reduced his musical output, making only one-off appearances on stage and in the studio. He sang in a duet of his 1971 song "Changes" with Butterfly Boucher for the 2004 animated film Shrek 2.During a relatively quiet 2005, he recorded the vocals for the song "(She Can) Do That", co-written with Brian Transeau, for the film Stealth. He returned to the stage on 8 September 2005, appearing with Arcade Fire for the US nationally televised event Fashion Rocks, and performed with the Canadian band for the second time a week later during the CMJ Music Marathon. He contributed backing vocals on TV on the Radio's song "Province" for their album Return to Cookie Mountain, made a commercial with Snoop Dogg for XM Satellite Radio and joined with Lou Reed on Danish alt-rockers Kashmir's 2005 album No Balance Palace.Bowie was awarded the Grammy Lifetime Achievement Award on 8 February 2006. In April, he announced, "I'm taking a year off—no touring, no albums." He made a surprise guest appearance at David Gilmour's 29 May concert at the Royal Albert Hall in London. The event was recorded, and a selection of songs on which he had contributed joint vocals were subsequently released. He performed again in November, alongside Alicia Keys, at the Black Ball, a benefit event for Keep a Child Alive at the Hammerstein Ballroom in New York. The performance marked the last time Bowie performed his music on stage.Bowie was chosen to curate the 2007 High Line Festival, selecting musicians and artists for the Manhattan event, including electronic pop duo AIR, surrealist photographer Claude Cahun, and English comedian Ricky Gervais. Bowie performed on Scarlett Johansson's 2008 album of Tom Waits covers, Anywhere I Lay My Head. On the 40th anniversary of the July 1969 moon landing—and Bowie's accompanying commercial breakthrough with "Space Oddity"—EMI released the individual tracks from the original eight-track studio recording of the song, in a 2009 contest inviting members of the public to create a remix. A Reality Tour, a double album of live material from the 2003 concert tour, was released in January 2010.In late March 2011, Toy, Bowie's previously unreleased album from 2001, was leaked onto the internet, containing material used for Heathen and most of its single B-sides, as well as unheard new versions of his early back catalogue. 
Question: What are the names of the people who sang a duet of the song "Changes" for the 2004 film Shrek 2?
Output (English): Bowie.