The starling, the roof tile and the bottle

Today engineer Jansen risked his life (again) on a wobbly ladder. There is a roof tile that missed the blob of cement on the outside, and a smart starling noticed that, and thinks: nice habitat! It is right, but it's already mince. And I don't want any vandal starlings with a nesting urge. That only gives us grit in the house. These roofs are not more than a layer of gypsum/clay on reeds under roof tiles. At the arrow an old 2-liter cola bottle was inserted up it's front door. Soon the roof will be maintained a bit, and the opening closed with cement again.