When the patient arrives, it can barely move its body. Sometimes it can’t blink. Vibrant green wings falter as the parrot tries—and fails—to fly. A nurse props up the bird’s limp, violet-blue head on a makeshift cushion and slides a bowl of nectar in front of its bright red beak. It is just one of dozens of rainbow lorikeets being treated for a mysterious paralyzing illness at this wildlife hospital in eastern Australia.
Thousands of the birds are afflicted every year in the region, where they are a fixture in backyards, chattering away as they feast on Moreton Bay figs, gum tree blossoms and countless other plants. Around 40 percent of rainbow lorikeets that present with a severe case of this unexplained paralysis won’t survive. For those that do, rehabilitation can take months.
Cases of what is called lorikeet paralysis syndrome (LPS) have been increasing over the past decade, says veterinarian Claude Lacasse of the RSPCA Wildlife Hospital in the eastern Australian city of Brisbane. It is now considered one of Australia’s most significant wildlife diseases. But scientists are baffled as to what is causing it.
Lacasse has partnered with several researchers to try solving the mystery. So far, they’ve ruled out hundreds of human-made chemicals such as pesticides, as well as various infectious diseases. Their current hypothesis is that LPS is caused by a plant the birds are eating, something that flowers or fruits between late spring and early fall—when cases always rise. But researchers have no idea which plant or plants might be involved, why the disease is getting worse or whether climate change is playing a role (by, for example, increasing the spread of plant pathogens).
For now, the priority is figuring out everything the sick lorikeets are eating. “We’re approaching this like a veterinarian investigating a patient,” says wildlife health and conservation professor David Phalen of the Sydney School of Veterinary Science at the University of Sydney, who, along with Lacasse, is leading the research into LPS. “Only it’s not just one patient. It’s a whole flock.”
Native to Australia’s eastern seaboard, rainbow lorikeets dwell in forest and scrubland and in leafy coastal suburbs. They are the country’s most common backyard bird. The charismatic parrots typically drink the nectar of the fragrant blossoms of native trees and shrubs. But widespread habitat loss, heavy rains that damage blossoms and severe wildfires have increasingly driven lorikeets to other food sources, including fruit, seeds and, strangely, even meat. This increasing variety in their diet is one reason it’s so difficult to identify what’s making them sick.
To take on the mystery, Phalen and his team set up a citizen science project on iNaturalist, a social network for biodiversity observations, asking people in LPS hotspots to take photographs of wild lorikeets feeding on plants.
Molecular ecologist Rachele Wilson, an adjunct research associate at Griffith University near Brisbane and now a postdoctoral fellow at the University of Queensland, came across a paper Phalen and Lacasse had written and realized she could complement the search efforts using a technique called DNA metabarcoding—which in this case involves testing DNA in sick birds’ droppings to match it to specific plant DNA “barcodes.” In 2022 Wilson completed a proof-of-concept study with eight lorikeet samples. These data, combined with iNaturalist observations, suggest the birds are feeding on more than 130 plant species, at least 30 of which are potentially toxic.
Wilson, Phalen and their colleagues are now working on a study with samples from another 40 LPS-affected birds and comparing them with droppings from healthy lorikeets. The researchers are not just looking at plant DNA this time but also at fungal, bacterial and animal DNA to allow for the possibility that the birds are ingesting a venomous insect or spider in fruit, or a toxin produced by fungus or bacteria found on a plant. “It’s possible it’s not the plants themselves but a plant pathogen,” Wilson says.
Some of the most toxic biological compounds known to exist are produced by fungi, says Simon Cropper, an ecologist based in Melbourne, Australia, who is also volunteering his time with the LPS project. And a 2021 study in Nature Climate Change showed that climate change is increasing the spread of plant pathogens, including fungi, around the world. Several fungal diseases can affect the Brisbane area’s Moreton Bay figs, although it’s not yet clear whether any of these could be the culprit behind LPS.
It’s possible climate change could also be playing a role by driving rainbow lorikeets to seek out unusual food sources. Climate change can cause devastating misalignments when animals that pollinate specific plants fall out of touch with seasonal cues. And though Cropper hasn’t seen anything in the scientific literature about this happening in Australia’s northeastern state of Queensland, where Brisbane is located, he says he does see it in wildlife in the southeastern state of Victoria. Animals “are broadening their foraging range and going into more traditionally uninviting and unnatural areas to try to get food and keep alive,” he says.
Another twist in the paralysis mystery is that flying foxes—a type of fruit bat that is usually nocturnal—are also being found with symptoms resembling LPS. “Basically, bats are the lorikeets of the night,” says Jane Hall, wildlife health project officer at Taronga Conservation Society Australia, a nonprofit whose experts investigate wildlife mortality events and are involved in LPS research. “Whatever the lorikeets are feeding on in the daytime, the bats are feeding on in the nighttime,” she says. “So it’s really interesting that the bats are presenting with similar clinical signs.”
According to the Queensland government, flying foxes eat flowers, fruit and leaves from more than 100 native plant species. “If it turns out that there’s some overlap between what the [sick] flying foxes and the lorikeets are feeding on, that might give us another clue into what might be causing this,” Phalen says. He hopes all the information being gathered by the lorikeet and bat paralysis investigative teams will eventually start to coalesce and that the culprit will soon be found. With climate change causing more extreme weather events and intensely hot summers, the need to find what’s paralyzing the iconic rainbow lorikeet—and potentially other species—is of urgent concern.
“They’re amazing birds,” Phalen says. “They’re smart. They’re entertaining to watch. They’re beautiful. It’s hard to see them as sick as they are. But at the same time, they’re battlers.”