In numerous early episodes of Sons of Anarchy, Gemma Teller is shown to own a cockatoo (an umbrella, IIRC).
In at least one episode (in either season 4 or 5), the same cage is suddenly occupied by a cockatiel. The cockatoo is never seen again.
At the end of season 6, the cage is now occupied by a crow. There are no signs of either the cockatoo or the cockatiel.
Thematically, one could argue that the species and color change tracks Gemma's progression (white -> gray -> black). But is there any official explanation to the the change in birds?