In 1982, I spent 34 days in Atol das Rocas, Brazil, amassing data for what later became part of my Ph.D. dissertation on gastropod mollusks from Brazilian oceanic islands. The 89-acres atoll is inhabited by large populations of seabirds, including the Sooty Tern (Sterna fuscata). The photo shows one of their nests. Typically, in the absence of twigs, branches, and leaves, Sooty Terns use bivalve shells (mostly the Cross-barred Venus, Chione cancellata) and small coral fragments to "line" their simple nests. The shells might also help camouflage the eggs in the open environment of the atoll. Read more about mollusks and their shells in the Southwest Florida Shell Guide.