Polcokból emeletesodú is készíthető, mert vannak olyan madarak, amik telepesen is költenek. Ilyen madár a mezei veréb (Passer montanus), ennek készült ez az odú.
You can make storeyed cave too from shelves because there are such birds, which lay eggs here together. The Eurasian tree sparrow (Passer montanus) does it. This cave was made for it.
