These Cave Swallows were building their mud nests under the eaves of the pump station building near the Charleston Slough in Mountain View, California. I've always been intrigued by the mud nests of these birds, but this was the first time I've had the chance to get a close look at the build process. Muddy areas close to the building were continuously visited by the swallows. They would keep their wings in a vertical position while attempting to get a beak-full of mud to bring back to the nest site. The nests were at several different stages of construction; from just a few lines of mud on the wall to fully completed nests. Just have a look at what amazing nests these swallows build_one beak-full of mud at a time.