Poecile palustris (?)
Poecile palustris (Marsh Tit – Κστανοπαπαδίτσα) or Poecile montanus (Willow Tit – Βουνοπαπαδίτσα) ?
The identification-separation of Willow and Marsh Tit is one of the more challenging in the field.
Here is a scientific paper about the challenge of the separation of these two species in the field. Several identification criteria used form a lot of guides, like the extension of the black bib, or the glossy or not cap, seem unreliable at least for the British birds.
Unfortunately i didn’t hear any call form this tit, which is the most secure separation criterion.
The white spot on the upper mandible is one of the reliable identification criteria with little overlap and could give more possibilities for a palustris here.