Eleanor

I would like to learn how to identify the "fliers" that I see every morning here in Boston.  Flying high in small groups, obviously catching insects, and chirping the entire time.  They never come low enough for me to see their color, and they never seem to land, so how in the world do you identify them?  They have the wing shape that I think of as a swift, or possibly a nightjar.  I can't tell how big they are because they are flying so high.  Does anyone know what bird this is?  Or have a suggestion for how to tell?  I'm sure anyone else looking up at in the Boston morning sky must see them every day too.