In the 1700’s diets were very different. It was quite common for individuals to consume puddings that contained stuffed game - including Colly Birds (which is another name for blackbirds).
Today, black birds are protected under the Wildlife and Countryside Act 1981, which makes it an offence to intentionally kill or injure them. For more information on this, please visit http://ww2.rspb.org.uk/birds-and-wildlife/bird-and-wildlife-guides/bird-a-z/b/blackbird/thelaw.aspx