Black-capped chickadee / Schwarzkopfmeise (Poecile atricapillus)

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Black-capped chickadee. 2023-10-13 14.45.40 New England
Classification: Genus Poecile; Family Titmice (Paridae)
This bird appears across the great seas in the following continents: Europe, North America.
I was surprised to see that the chickadees I saw in Maryland are not the same ones as in New England: Carolina and black-capped.Wikipedia says they 'most likely diverged about 2.5 million years ago'!

First documented observation : 2023-10-13 in New England.