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Junco hyemalis
Those photos and a check of my field guides still suggest junco to me. I can't think of any other juvenile species that it may be, but I have been wrong before.
I did some more searching and found that some do have dark sides to the tail underside. Check these pictures here http://www.oiseaux-birds.com/card-dark-e...
Junco was one of my thoughts but they don't appear to have dark sides to the underside of the tail feathers. Grosbeaks do but the bill seems the wrong shape for those.
It appears to be a juvenile dark-eyed junco. They look completely different from the adults.
Cardinalidae/Emberizidae/Fringillidae families of which there are many species, but the black-bordered white outer tail feather should narrow it down.