My true love sent to me: four colly birds, which are said represent the canonical gospels or the four evangelists, Matthew, Mark, Luke, and John.
In the song, 'colly' simply means 'black'. I suppose they could be rooks, ravens or crows. But when I think of blackbird I think of the Lockheed SR-71 spyplane that was given the same name. Developed in the mid-1960s, its black coating and distinctive shape, both designed to make it almost invisible to radar, made it also one of the strangest-looking planes in military service. Not that any of us actually saw one until thirty years later, because it was also one of the American military's most secret assets. It set an altitude record of 85,000 feet and flew from New York to London in less than two hours, a record speed of 2,300mph. It was so fast that it could simply outrun surface to air missiles. It was pioneering technology – a large number of the planes were lost to accidents and failures. But it was the sort of technology that won the Cold War. When it came down to it, a regimented Soviet society just wasn't so inventive. It could copy things, and make the best of simple technology, but it just couldn't keep up, and certainly couldn't keep developing new things over and over and over. Only competition produces that sort of constant innovation and improvement. We need more of it.