From what i can see of it it looks like a female blackbird with leucistic markings.In my experience Blackbirds can vary with some individuals having very streaky almost pinky brown markings on belly and breast.
Images of one of 2 mystery birds seen in a Manchester garden last month can be found on the 'Notice Board' on the website. I would appreciate any ideas from anyone with an opinion (and preferably a definative answer ) for the identification of these birds.