There were a ton of these guys on a small island where me, my brother and some friends set up a tent on a kayak trip a few weeks back. Apparently they are called Rödstjärt. Which translates to red butts in Swedish. The females were very active and (probably) tried to keep me away from their nests. I only say a few of the males (the two last photos), and the pictures of them were sadly not that good.