I can't help it, to me black birds represent bad thoughts (and I love ravens and co). Sometimes they just don't fly away and grow heavy on our heart. I don't see them as something wrong, they help us looking with a different point of view but when se get stuck with it, it only distort everything, even ourself turns into monsters.
We don't necessary want this, someday easy as that, a crow take a rest on us. Sometimes we grow beautiful, sometimes envy (lavander) grows on us.