'Flew' is the past tense form of the verb 'to fly'. In the context of a bird moving through the air, 'fly' is the correct verb. The sentence indicates that the bird departed a short time ago, so the simple past tense 'flew' is appropriate. 'Flowed' is the past of 'flow' (liquids), 'flown' is the past participle, and 'flied' is an incorrect form.