Fifty dead birds and thirty more visibly sick: those were the numbers that aerial surveillance recorded over Baudin Rocks, off the South Australian coast, before laboratory analysis at CSIRO's Centre for Disease Preparedness confirmed on Monday that Australia had suffered its first mass wildlife mortality event from the H5 strain of avian influenza. The confirmation came swiftly, drawn from samples taken from five greater crested terns and a single silver gull. Within hours of that announcement, the situation appeared to be moving again. Victorian authorities reported over the weekend that aerial observations had identified a cluster of dead and sick greater crested terns in the Glenelg River estuary near Nelson and across Lawrence Rocks, in the state's south-west.

The state's chief veterinary officer, Dr Graeme Cooke, noted a "clear increase" in the number of dead terns along that stretch of coast compared with only days earlier, when individual detections had first been reported. Samples are being processed, and a positive result would make Victoria the site of Australia's second confirmed mass mortality event. The region is of particular ecological concern: it supports breeding colonies of Australasian gannets and populations of seals, both of which have proved highly vulnerable to H5 strains elsewhere in the world. Environment Minister Murray Watt did not soften the outlook.

He acknowledged that wild bird movement makes geographic containment effectively impossible, and that further mass deaths should be expected. Scientists and wildlife managers who have watched H5 devastate seabird colonies across Europe, North America and sub-Antarctic islands will recognise that trajectory.