
Do you see what looks like holes in the side of this cliff? They really aren't holes, but they are birds' nests built from mud! These nests were built by Cliff Swallows. Click on the pictures for a full screen view.
Swallows kind of like to return to the same nest year after year, not always, but often. I think that's pretty interesting. Don't you?
Cliff swallows build mud nests attached to cliffs, bridges, buildings and other structures. This is particularly true of the cliff swallow—the swallow of San Juan Capistrano—which nests in large colonies of up to several hundred pairs. {UC Davis}
I wish I could have managed to get closer to take better pictures, but the river is really quite wide right here. I did find a site with wonderful pictures and even a little video that I'm sure you will enjoy. Look at The Birder's Report for more information.
