These remind me of andrea zittel's inverse pyramid of animal living units. Mainly so because they have circular cutouts and are stacked. I can't seem to find a photo reference on the web though. Thishttp://www.moma.org/images/collection/FullSizes/82413003.jpgis a living unit that she made for humans
I'm in the market for a nesting box. This one is very interesting. Architectural as well as functional.