Bluebird nestlings and a Titmice birthmarks

Photo #1 – April 18, 2023
This is a Tufted Titmouse on our umbrella pole; Its nest is in there. Last year, we had Titmice raise a successful brood of 6 in there, and looks like they’re going to nest again! The thing about this specific Titmouse is that, if you look closely, it has a black mark underneath its left eye. While this could just be something that smudged its feathers, I believe it is a permanent birthmark-like mark. The female from last year (photo #5) had a mark like this beside her right eye, so I think this is one of her offspring that inherited the birthmark. What do you think?