The owls are nesting in a old stone barn on the Ynis-hir reserve. The barn itself is no longer used and has a broken window which the parents fly in and out of.
Barn owls don't build much in the way of a nest, usually in nooks on cliffs or in holes of trees, or, not surprisingly, in barns.
We have 3 cameras within the barn, 2 on the nest and one on the window to see the parent arriving.
The chicks are different sizes because they have been incubated according to a strategy that boosts the family's chance of at least one owlet surviving the summer.
The video clip below from Springwatch 2011 explains it more fully.