Folks

To add to the discussions about the differences between Carolina and Black-capped Chickadee, I quote David Sibley, page 374, from The Sibley Guide to Birds. 2000.

"Overall, Black-capped is brighter, more colorful, and more contrastingly marked then Carolinas;  it is larger, fluffier [must be because it is colder], larger-headed, and longer-tailed, with darker tail and wings that have brighter white edges;  its check-patch is entirely white (Carolina blends to pale gray at rear, and it has a greenish back and buffy flanks (Carolina is duller grayish); its song is lower-pitched and its call slower.  All these features are relative and subject to variation, but in combination they should serve to identify most birds.  Hybrids are recorded in the narrow zone of overlap (there is disagreement over the extent of hybridization).  Song is learned, so not very helpful for identification as individual birds can learn the "wrong" song type. " 

There is also an article in the March/April Birding magazine titled A Closer...Listen: Unraveling Chickadee Vocalizations by Brian Taber.  I have not read the article yet but it might be helpful.

Good luck.

George