The European pied flycatcher (Ficedula hypoleuca)
These birds nest in old hollows of woodpeckers and tits, under the roofs of houses in villages, as well as in the natural crevices of trees. What you can see in the photo.
Passing by, I noticed how the bird quickly hid in the bark of a tree. At first I thought that it seemed to me, but after a while a bird crawled out of this gap and flew away.
And after some time the female flew there. You see her on this 2nd photo.
And so they periodically flew back and forth. It became clear, and that they made a nest here, and flew away for food to the chicks.