Along the southeastern coast of South Australia, seven greater crested terns — birds that nest in dense colonies and do not migrate away — have returned suspected positive results for bird flu, a development that may signal the virus is no longer merely passing through Australia but beginning to settle in. With twenty confirmed cases already scattered across four states, authorities are watching closely as the breeding season draws thousands of these birds together, knowing that what moves through a wild colony can, in time, reach a farm. The machinery of detection is working; the machinery of