Clue: Worst witch in Gryffindo keeps chasing the odd owl etc (9)
Answer: TWITCHING
Explanation: Definition: chasing the odd owl etc
A hidden answer ('keeps') in 'wors**T WITCH IN G**ryffindo'. A twitcher is a birdwatcher principally interested in spotting as many rare species as possible. Maybe it is just the Grauniad, but the house (and sword) in Harry Potter is Gryffindor.