Mutant bird is one of the mutants created by Dr.Animo in Washington BC Episode
Ben 10
When Dr. Animo assaulted a supermarket in Washington, with his Mutant Frog, then Dr, Animo mutated this bird and a hamster. Its appearance and size changes and becomes a giant canary Dr.animo uses to kidnap Gwen, but she is saved by Stinkfly.
When Dr.Animo is the Museum, where this revives a Tyrannosaurus and a Mammoth, Gwen fights with the bird, once the transmuter was destroyed, the bird returned to the normal.