Growing on birch bark, possibly in association with the bright-yellow powdery lichen, that might be Chrysothix? In the past, I have found this lichen growing on spruce with Chrysothix as well.
Photo taken with a cheap digital microscope so picture quality isn't the best but its okay. These little guys measured about 1mm tall. I would definitely suggest getting a handheld scope, I do use a 10x hand lens in the field but the digital scope is really handy and doesn't cause eye strain.
