Coal tit (Periparus ater).
This bird is one of my favorites!
He is much smaller than the big tit.
It is long with the tail up to 11 cm. and weighs 10 grams.
It usually hides in tall pine branches and is difficult to monitor.
By the way, in Bulgaria this bird has two names: Coal tit or Pine tit.
His second name is because of his habitat on pine forests.
It rarely goes down into populated areas.