What instrument was Ian Anderson skilled at playing besides the acoustic guitar?

His tendency to stand on one leg while playing the flute came about by accident, as he had been inclined to stand on one leg while playing the harmonica, holding the microphone stand for balance. Anderson became known for his famous one-legged flute stance, and was once referred to as a "deranged flamingo".

At this time Anderson abandoned his ambition to play electric guitar, allegedly because he felt he would never be "as good as Eric Clapton". As he himself tells it in the introduction to the video Nothing Is Easy: Live at the Isle of Wight 1970, he traded his electric guitar in for a flute which, after some weeks of practice, he found he could play fairly well in a rock and blues style. According to the sleeve notes for the first Tull album, This Was (1968), he had been playing the flute only a few months when the album was recorded. His guitar practice did not go to waste either, as he continued to play acoustic guitar, using it as a melodic and rhythmic instrument. As his career progressed, he added soprano saxophone, mandolin, keyboards and other instruments to his arsenal.

His famous tendency to stand on one leg while playing the flute came about by accident. As related in the “Isle of Wight” video, he had been inclined to stand on one leg while playing the harmonica, holding the microphone stand for balance. During the long stint at the Marquee Club, a journalist described him, wrongly, as standing on one leg to play the flute. He decided to live up to the reputation, albeit with some difficulty. His early attempts are visible in The Rolling Stones Rock and Roll Circus film appearance of Jethro Tull. In later life he was surprised to learn of iconic portrayals of various flute playing divinities, particularly Krishna and Kokopelli, which show them standing on one leg.