My dryer recently stopped doing a good job, and I've heard bird activity in the vent. I had to reach way, way into the vent (would have been easier to detach the duct from the bathroom, really) to even reach any nesting material. What I pulled out were loose grass, sticks, and some eggs. Everything fell about 20 feet to the ground, and 2 of the eggs broke. The two remaining ones are nearly identicle in color, size, and shape to the robin's egg in the photo. But I thought robins liked to nest in trees (plenty of those around here) and line their nests with mud?