Willie-wagtail

Oh! Thank you.

I'd assumed you were just using it's standard nickname (e.g. Jenny Wren or Robin Redbreast). I wonder whether it is named from it's cousin's English nickname. As an example of that, Robins were once just "Redbreasts", got nicknamed Robin, and somehow, the nickname became the standard way to name them. As you can perhaps tell, this derivation amuses me