Some years ago we had breeding magpies which were completely black. We initially thought they might be a cross between a crow and magpie, but analysis of a dead one showed it was a differently pigmented magpie. They were here for about 10 years and then disappeared, although we do occasionally see some on one of our neighbour’s properties. Most people don’t notice they aren’t a crow, but the magpie characteristics are obvious when you are looking for them.
Did you know that the Australian Magpie is a ‘mate for life’ species?
However, if the pair loses the male (while they have young), the female will quickly replace him with whoever else is handy, and the replacement usually does a better job of looking after the young. http://www.abc.net.au/radionational/programs/offtrack/the-secret-life-of-australia’s-marvellous-magpies/6750736