Brown Thrashers are good mimics, heard one last week doing a Red-bellied Woodpecker along with other calls .
Also some Blue Jays can mimic some birds.
I've heard this about "Brown Thrashers", There was a pair of them near the beach two years ago in an area of thick hedges. At that time they were not singing. Unlike the vids i just watched on Youtube, I guess i am going to have to see the bird.
This bird was mimicking two or three calls, sounded similar to the mocking birds at Downsview.
Last time I saw a "Cat Bird" is was making this sound
https://www.youtube.com/watch?v=Fu1gNlGjoos without the clucking. lol