One of my hens (actually, still a pullet until April), sneezed a half dozen times this afternoon, then stopped. She had been scratching and digging along side of a rock row, then suddenly started sneezing as if she inhaled something very dusty. It cleared up as suddenly as it began, but I was concerned. Camille is my best layer. I suspect the exhaust of my truck could have been a factor as well, as they were milling around while I was unloading some brush. Exhaust makes me sneeze, too.
They've all gone to bed now and no one has sneezed again. I'll keep an eye on them tomorrow just in case it recurs.