Yes, there's more than one type of bluebird. In the US, you have the Western, the Eastern and the Mountain Bluebirds.
I tend to lean towards picking west coast varieties for my sets since those are my birds (the Western Bluebirds are in Characters v1). For years, I have had people asking for the Eastern Bluebird so when I created the other "Characters" sets (
which are the only things in my Renderosity store right now), I tried to balance the scales a little. The "Characters" sets within my SBRM family of products specifically feature popular US birds.
The Mountain Bluebird is in "Birds of Legend" set (being that "Bluebird of Happiness"). Hopefully I'll get to that update soon. Technically, there are even more US bluebirds if you want to split hairs and get into subspecies (which often gives you the exact bird you're seeing out your window); and again the ones that appear in Songbird ReMix sets tend to favor the Northeastern edge of Los Angeles where I live.
As for your chickadees, the chickadees of New England are the Black-capped Chickadee (which is found in the base "Songbird ReMix" set) along with the Mountain Chickadee which I get. The only other East coast chickadee is the Carolina chickadee which is found in the southern East coast. It looks really, really close to the black-capped. Apart from location, look for slightly browner wings, less white fringes on the secondary wing feathers and a slightly smaller tail on the Carolina chickadee.
BTW, did you know that the Black-capped chickadee is the most "advertised" bird in the US? That chickadee appears in more imagery than any other US bird... the Northern Cardinal is the runner-up.