Willow tit / Weidenmeise (Poecile montanus)

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Willow tit. 2020-04-25 08.51.40 Luppmen
Classification: Genus Poecile; Family Titmice (Paridae)
Vogelwarte.ch says, Two forms of Poecile montanus exist in Switzerland: the Willow Tit occurs in the Jura, the Pre-Alps and locally on the Central Plateau, while the Alpine Tit is confined to the Alps. The two forms have a distinct song as well as different ecological requirements, and could evolve into two species over time. Since I've heard them in St. Moritz, they're more properly alpine tits than willow tits. I should verify the audio recordings vs xenocanto, etc, as it was BirdNet that identified them as willow tits, and it is not infallible.
Vocalization:

Other sounds: high pitced "zi zi" similar to other tits. [Link]
Song:

1.Gesangstyp: „ziü ziü ziü „ etwas wehmütig, die einzelnen Töne leicht absinkend, nicht klappernd. Bei Unterart Alpenmeise auf gleicher Höhe bleibend. 2.Gesangstyp: variable, schwätzende, helle Folge m. trillerndem Schluss. [Link]

Song: One or two soft, clear, melancholic notes repeated in a slow, even rhythm. At first rising slightly in pitch, then gradually falling. In some areas song is evenly pitched. [Link]
Calls:

Folge v. etwas heiser näselnden „zi zi dääh dääh. (einmalige Laute) [Link]

Call: Most characteristic call a frequently uttered, nasal "ti ti chaa chaa chaa". First notes high pitched and the following lower, coarse, nasal and drawn. Sometimes uttered without the introductory high pitched notes. [Link]
Physical details: length=11 cm, wingspan=17-20 cm, weight=8-14 g
Habitats: Forest

Song: Songs I've heard alternate two notes and look like a sine wave on the sonogram. Vogelwarte.ch: Apart from minor differences in diet and size, Alpine Tit and Willow Tit can only be identified by their song. The Willow Tit utters a series of long, descending notes («tyoo tyoo tyoo tyoo»), whereas the Alpine Tit’s territorial song consists of short notes on an even pitch («dee dee dee dee dee»). See more here.
Song attributes: Melody: simple rhythmic, slow, Frequency: 3-7 KHz
♫ (song)