We had been driving along the Bay of Wrecks on the eastern coast of Christmas Island for over an hour and a half when we saw the flock of terns. A few were scattered over the pale tarmac in front of us, but thousands more were wheeling and hovering in the air, suspended above the saltbushes of the island’s interior. ‘Sooty Terns,’ Perry Langston said from the passenger seat beside me. I stopped the car and turned off the engine, leaving the air conditioning washing over us. ‘Must be one of their nesting grounds.’ For a few minutes we sat there watching them contract and expand in the air. At their tightest point they looked more like a swarm than a flock, turning the sky a flurry of living black.