Return of the swifts!

As site administrator and geeky recent convert to bird watching, I reserve the right to report on bird stuff that happens off campus. My swifts are back. We got a new furnace several years ago, and a colony of swifts has been making a summer home of our now-unused old brick chimney for three summers, counting this one. I noticed them again about a month ago, but I think their numbers have increased, as I hear them above and see them several times every day, particularly at dusk when they circle and finally dive into the chimney. Are they chimney swifts or Vaux's? How do you tell? They appear as a near-perfect crescent when in flight, with a tapered tail. The last two years, when the hatchlings came of age, I could hear a surge of shimmery peeps coming from my pantry when the adults came home to feed the young. Standing next to my refridgerator and listening to a chorus of swifts in my kitchen is just good news all around.