The Cliff Swallow: Bird Engineer. Instead of choosing a home safely tucked into a bird house or a tree branch, cliff swallows live life on the edge, a vertical edge that is. Cliff swallows construct their nests out of mud, mixed with saliva in their beaks and placed one bead at a time into a round, chimney-like structure that is often mistaken for a bee’s nest. Although natural rock faces and bluffs are commonly selected sites, cliff swallows are just as comfortable building their nests on buildings, bridges, and other man-made structures. In Horicon, cliff swallows regularly build their nests right on the visitor center building. More often than not, cliff swallows will nest in groups, so if you spot one, there is a good chance others are nearby. Like other swallows, cliff swallows are insect eaters and will catch them on the fly, open hunting near or over open water. Horicon Marsh has several swallow species, which can sometimes be hard to tell apart when flying quickly. Each swallow species has a unique nest building style, and the cliff swallow nests are very distinctive. Through binoculars, our nesting sites offer the chance to not only watch exciting in-air hunting, but also watch the parenting of these daring birds.