Safety is also a factor and not to be forgotten Comfort.
The construction of the nesting boxes and where we site each box should take all these factors into consideration.
As birds will not only use the nest box for nesting, but often use the boxes in winter to roost in, we need to avoid extreme temperatures. Too cold a position will more than likely mean the box won't be used for nesting or roosting.
An adequate nearby supply of food and water is also a big plus in helping the parents to not only meet the challenges they face in rearing their young but also surviving the winter.
Nesting boxes are a real asset in the wildlife garden.