Predators such as crows, gulls and owls wait for parents to leave the nests so they can take the eggs or chicks. The low brush that grows on dunes at the beach is missing on roofs, leaving no place to hide from predators and no shade from the baking sun. The light, gravel surface isn't deep enough to cushion the eggs as a sandy beach would. The roofs have a limit. Many chicks fall off unprotected edges as they run after a parent that leaves to get food.
Heavy rains mean temporary flooding of their homes, which are mere scrapes in the gravel.
Most of the 150 or more birds nesting on Building One are least terns. The Florida Fish and Wildlife Conservation Commission lists them as a threatened species, a little better than endangered, the last adjective before extinction. The least tern comes by its name naturally. It is the smallest tern in the world at 9 inches. It's mostly white and silvery with a mask of black on its face.