When you're the premiere voice in Irish trad-pop, you get to celebrate your 50th birthday any way you'd like. And if you want to celebrate by playing backup for indie-folkers and alt-country youngsters and, um, astronauts (literally -- see track 14), well, we'll just sit back and listen. We'll grin through the few slightly clunky duets (hi, Imelda May and Pistol Annies), and revel in the ones that fit like a glove (Punch Brothers, Carolina Chocolate Drops, anything retracing the band's Irish folk/bluegrass steps). Their birthday gift to us? The Chieftains-only "Reunion" breakdown.