[Raven]

for those of you that enjoy building Bird houses otherwise known as Nest boxes......

I have found a Certain trick that encourages birds to take up residency

and that is to create a U shaped bottom with a thinner material
by either back cutting it if using wood ...so it will bend.....

or selecting a material that will bend on it's own...

some moisture getting in is desirable from the parent birds perspective
because the eggs need a bit of moisture to develop...