It sounds like a recently fledged Blackbird which would look like a lot the female (brown and mottled rather than black), but without the tail feathers, see:
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In which case what you are seeing is a perfectly normal stage for a young bird, once they have matured to a certain level they will leave the nest, whilst still being cared for by the adult (what you are seeing with the Male bird continuing to feed it), as they learn to feed and fly on their own.
http://www.rspb.org.uk/advice/helpingbirds/health/babybirds.aspx
this, leave nature alone.