The sign asks us not to disturb the birds. Understandable. It’s easy to miss the nests a couple of feet above your head until your hair’s parted by an incoming house martin.

They slalom the red sandstone ruins, metallic blue flashes in the morning sun. Occasionally one jinks up to the corner, disappears into the nest to meet the needs of demanding mouths, emerges and darts away again, a sleek silhouette against a backdrop of water.

Tantallon Castle has perched on a promontory overlooking the Firth of Forth for 700 years. For more than half that time it’s been a ruin, besieged by Oliver Cromwell and never repaired. Its remnants are home to dozens of house martins. Their national numbers are in shocking decline, but here they retain a stronghold. They build their mud cups – marvels of engineering held together with saliva and hope – raise their broods, then wing it back to Africa, their exact wintering location still largely mysterious. Their ancestors saw battles and banquets. Now their summers play out to a gentle flow of tourists.

Gannets diving next to Bass Rock. Photograph: James Glossop/Edinburgh Napier University/PA

A mile across the water sits Bass Rock – a quietly monumental, broad-shouldered icon, its distinctive shape speckled white with birds and guano. To Bass Rock, the castle’s a mere whippersnapper. With 340m years under its belt, it’s seen everything. Mainly it’s seen gannets, whose scientific name, Morus bassanus, bears evidence of the close association. Around 100,000 call it home – it used to be more, but bird flu has denuded their population since it hit in 2022. A recent study by the RSPB (now the island’s owners) and Aarhus University reckons it will take the population at least 15 years to recover. For the survivors, a strange remnant: their vivid blue irises turn black.

Across the water they swarm the island like midges, wheeling round in broad arcs. Up, turn, pause, tuck wings, plunge – sleek bullets producing the merest splash. Around me the martins snap up invisible insects in midair.

These hunting skills are virtually mystical to us, second nature to them. Survival is hard, and getting harder. But give these birds half a chance and they’ll rebound. Half a chance – it’s better than none at all.