A virus older than memory is moving through southern Australia's coastline, claiming thousands of wild birds and testing the resilience of species that have never encountered it before. H5N1 avian influenza, already devastating wildlife populations across the Northern Hemisphere, has arrived in a continent whose animals carry little immunity and whose remote habitats make observation difficult. The question science is now asking is not simply how many will die, but whether the losses will be ones a species can survive — and whether we will measure carefully enough to know the difference.