Along with the fox discovered in Adelaide, a little penguin was among new suspected "events" of the deadly strain reported by South Australian authorities on Wednesday.
Bird flu reporting in SA is now based on events, rather than individual animal detections, and may involve one or more animals.
There were no H5 bird flu detections in poultry or other livestock and the risk to human health remained low, the SA government said on Wednesday.
However, there are concerns over the threat posed to Australia's native scavenging animals after the suspected fox case.
Foxes and feral cats may be potential "super spreaders" of the virus, leaving quolls and Tasmanian devils vulnerable, the Invasive Species Council said.
Tasmanian devil numbers have been decimated by a deadly facial cancer and the species is listed as endangered.
"Finding bird flu in a fox is a serious warning about what this virus could mean for Australia's scavenging animals," the council's Rob Brewster said.
"Quolls and Tasmanian devils will all scavenge dead wildlife, potentially putting them directly in the path of this virus as bird deaths increase.
"All of our quoll species are low in numbers and surviving in very fragmented populations, while foxes and feral cats are everywhere - and are likely to become super-spreaders."
Mr Brewster called for a co-ordinated, national response to foxes to ensure wildlife populations were as resilient as possible to the looming threat.
"If we don't manage foxes and feral cats now, we risk further declines and local extinctions in our own unique scavenging marsupials," said Mr Brewster, reiterating calls for a federally funded $200 million wildlife resilience fund.
SA has 195 confirmed and 41 suspected bird flu events.
The new suspected infections included the fox at Osborne in Adelaide's west, a little penguin and a raven on the Limestone Coast, a Pacific gull on Kangaroo Island, and a greater crested tern at Coonalpyn.
Samples from the cases have been sent to the CSIRO's Australian Centre for Disease Preparedness, with results expected in coming days.
South Australians are encouraged to continue being vigilant in reporting sick and dead birds and other wildlife, but to avoid touching them as a vaccination program ramps up.
Up to 100 native birds at Cleland Wildlife Park south of Adelaide have been approved for vaccination across more than 30 different species.
Captive orange-bellied parrots, which has a wild population of fewer than 100 birds, and regent honeyeaters - which number fewer than 400 - are among the species approved.
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