Attack of the monster birds

I made some papier mache birds a few years ago, as Christmas decorations but a couple somehow turned out as monsters that would have scared the horses and so they ended up on the rooftop, as guardians of the strawberries instead. What's strange is that while the wren-type monster has stayed untouched, the robinesque monster has been repeatedly pecked and turfed over. You can see some of the stabs in this photo. I put two and two together when I watched a robin land there, check out the fake pretender to the territory and fly off again. I've read how territorial robins are and that they will size up to any small patch of red that could be a rival.