It's true. I used to have a canary as a pet, so I know from experience. When I first got LB, she (or he, I was never positive of my canary's sex and didn't want to check) the bird cage was in the hallway next to a big mirror and in the morning when I took the cover off of her cage (I needed to cover the bird cage with a big sheet at night, otherwise she would never fall asleep), LB would fly around a bit, stretching out her wings and then notice the canary in the mirror and get really, really upset. She'd tweet and twitter and puff herself up into a big, orange ball of feathers to try to scare the mirror bird away (maybe she was a boy) and when that didn't work she'd angrily try to attack and crash into the side of the cage. She only did it for two or three days because, my mom made me put up a scrap of wallpaper between the bird and the mirror, but that's why I think that holding up a mirror to a little bird is mean.