That's what Im dreading doing (making my pond). Yea they dont have to be triangle shape. But darned if out of all the different boxes to chose from that's the one they use. And I only made one so maybe there is something to it. I have never been able to find a pic of a wild bird nesting site. All my manderin boxes have hinged tops cause I will pull eggs from them alot (either to double clutch or to put rare duck eggs under them for them to hatch. I kept only 5 breeding pairs for this year.