Experts don't know what causes it or why, but a virus that spreads quickly in close contact is causing rainbow lorikeets to "drop out of the sky" across South-East Queensland.
Bird expert Darryl Jones from Griffith University said the condition, known as lorikeet paralysis syndrome or clenched-foot syndrome, was happening "really widely".
"There are lots and lots of cases in Brisbane at the moment. I'm pretty much inundated by things," Professor Jones said.
He said while it was not related to COVID-19, it had an important similarity in that it spread quickly when the birds were in close contact.
"It is a disease — it gets spread between animals, and the problem is [lorikeets] aren't good at social distancing very much at all."
The severity of the disease can vary between birds but it can lead to them dying "pretty horribly".
"Some of the birds, because they can't fly or walk properly, will fall out of the sky," Professor Jones said.
"They have a clenched claw, so they can't land and hold on to a branch: that's the simple problem.
"They fall to the ground and starve to death or a predator gets them or ants get them.
"It's a pretty horrible way to go."
RSPCA spokesman Michael Beatty said the rescue service had seen many cases of it.
"At any given time, we will have 30 lorikeets in [the wildlife hospital] because of it," he said.
Professor Jones said experts did not know what was causing it, but it had been known to occur at different times in eastern Australia since the 1970s.
This year the cases were predominantly around South-East Queensland, with cases also being reported on the Sunshine Coast.
He said if a person found a bird lying on the ground and it appeared to be dead or injured, it was still worth taking to a vet.
"The treatment can vary, depending on how badly they are affected."
Professor Jones said feeding birds was — and wasn't — the problem.
"It's not the feeding itself; the problem is we bring them in together.
"Just as we thoroughly know now with [coronavirus], anytime we bring animals together in one location, we spread the virus."
He said it was thought some of the birds' natural foods might be the origin.
"There is an enormous amount of natural food out there, flowers of every sort, but somehow it's causing a disease.
"We don't know the link — we know what it is, but we don't know what is causing it or why."
