Mr. Neil's Showy Mountain Ash & Fuzzy Leaves

Hey, any readers have any idea what this fuzzy stuff is on a leaf. I found it on several leaves of the same plant. It was on the underside of the leaf and the fuzz balls appeared fixed to the spot. Is this some type of gaul? Insect egg sac? Fungus? Alien life for that will take over my body and cause me to point and scream a la Donald Sutherland in the 70's version of Invasion of the Body Snatchers? Inquiring Birdchicks want to know.

Mr. Neil has a show mountain ash or rowan tree as he likes to call it. The berries are ripe and the birds are ready to pluck. This young robin spent a good chunk of Sunday in the tree. Amber was with me and she pointed out that every time the young robin was around, a young rose-breasted grosbeak was nearby. If the robin flew away, the grosbeak soon followed. We wondered if the robin and grosbeak were forming their own mixed flock and figuring out this whole survival thing together.

Waxwings, like this young cedar waxwing were getting in the berry action as well. I wish I had more time to digiscope them. While watching their antics in the tree, a ruby-throated hummingbird flew in and systematically tested all the berry clusters for nectar potential. It flew away disappointed but would periodically return--how could something that bright not have any nectar? Must be hard for that tiny brain to process.