On 12 January 1843, a Royal Navy survey expedition under Captain Francis Blackwood, working the eastern margin of the reef in the corvette Fly and the cutter Bramble, came upon a low green cay alive with wading birds. They named it Heron Island. The birds, as it turned out, were mostly reef egrets, not herons, and the only true heron ever seen here is a rare vagrant blown in from the mainland. The misnomer stuck anyway, the way sailors' names do. There is no evidence that Aboriginal people ever lived on or used Heron Island; it lies too far from the coast, a green dot in open water that the surveyors charted not as anyone's home but as a hazard to be mapped, one more reef to be made safe for ships.

Heron Island is, in a real sense, made of birds. During the summer breeding season, more than 200,000 of them descend on this tiny island, and tens of thousands of wedge-tailed shearwaters, the moaning, burrowing seabirds Australians call mutton birds, dig their nesting tunnels through the forest floor. That constant churning is why the cay has such rich soil for a coral island: the birds turn the earth, mixing the humus and stopping the formation of the hard, barren phosphate pan that would otherwise seal the ground. Black noddies crowd the Pisonia trees overhead. The whole island, by the height of the season, is a single vast rookery, the air thick with wings and the night loud with the eerie wailing of shearwaters calling from underground.

If the birds own the forest, the turtles own the sand. Heron Island is one of the great green turtle rookeries of the reef, where in summer the females haul their bodies up the beach in the dark, dig, lay, and return to the sea, and weeks later the hatchlings boil out of the sand and scramble for the waterline. The reef around the island has become a kind of natural laboratory for this and a thousand other questions. Researchers have even shown how warming sand skews the sex of hatching turtles, a finding with sober implications for a heating world. The waters draw divers and snorkellers to a resort on the island's northwest corner, but the turtles were here long before the resort, and the whole eastern half of the cay is protected national park, left to them.

In the island's southwest quarter stands one of the world's principal coral reef research stations. The Great Barrier Reef Committee established it in the 1950s, and the University of Queensland has run it as a partner since 1970, building laboratories, aquaria, and, in 2010, a facility devoted to studying how reefs will fare under climate change. A fire tore through the station in 2007, injuring no one, and the rebuilt labs reopened by 2009. David Attenborough filmed here in 2014 for his series on the Great Barrier Reef, drawn, as the researchers are, by the sheer concentration of life within wading distance. Few places let scientists step off a veranda and into a reef this diverse. Fewer still send their portrait into interstellar space as a calling card for the planet.