Solo, thanks for good sites!
I summarize mine sites (got from this forum also in previous years)
Willow tit Poecile montanus, former Parus montanus Буроголо́вая га́ичка, пухля́к (in latvian pelēkā zīlīte or "grey" tit)
Marsh tit Poecile palustris, former Parus palustris Черноголо́вая га́ичка, боло́тная га́ичка, га́ичка (in latvian purva zīlīte)
Tatyana, there are items also in russian.
http://www.ebirds.ru/vid/375.htm
http://www.ebirds.ru/vid/374.htm
And some items in english:
using a bill criterion (the same which Solo put here)
https://www.tandfonline.com/doi/pdf/10. ... 08.9674382
all criterions – look at the pictures in comments!
https://community.rspb.org.uk/wildlife/ ... willow-tit
and full paper here
https://www.britishbirds.co.uk/wp-conte ... h-Tits.pdf
But in reality it is not so easy, but I suppose these grey are different tits… is it true?
