American cliff swallow (nest)

Swallows deposit mud pellets onto the nest with a shaking motion leaving behind well-formed nuggets that bond with the others and harden into a strong nest wall. Technically called an adherent cup, a finished nest contains over 1,000 mud pellets. Cliff Swallows tuck their nests away in corners and make sure that the nest opening is small so the eggs and nestlings are well protected from predators.