Birds have very sensitive respiratory systems (which is why canaries were traditionally taken into mines to detect toxic gases). Given the prevalence of fires in these Australian bush habitats, it’s not unreasonable to expect birds in those areas to be extremely intolerant of smoke, allowing them to fly away and escape long before the fire gets close enough for them to feel the heat.
That seems plausible, but it doesn't seem to be what's happening.
The author of the 480 million affected animals estimate has co-authored an article which talks about the impact on birds (as well as many other animals).
The relevant quote from the article:
One might think birds and other fast-moving animals can easily escape fires. But smoke and strong winds can badly disorient them, and mass bird deaths in severe bushfires are common.
We saw this[0] in the current fire crisis, when dead birds including rainbow lorikeets and yellow-tailed black-cockatoos washed up on the beach at Mallacoota in Victoria.
The Age article referenced has more graphic detail:
Following the fires that have torn through the region, bird carcasses – perhaps in their thousands – have washed up on Mallacoota's once-pristine beaches.
Mr Semmens, 87, has counted 100 dead birds from 25 species on a half-kilometre stretch of Tip Beach, just outside Mallacoota, half-buried in blackened piles of leaves. “It’s a sorry sight,” he said.
And he has only viewed a small section of the beach following the fires – he estimates that "thousands" more birds would have died in the area.
“The birds who avoided the firestorm are struggling to survive about the town, where residents are putting out water, seed and fruit, hoping it will save some of them.”
