Darwin vets are hoping to solve an annual mystery that sees scores of colourful lorikeets act drunk and hungover — and then often die.

This illness affects the native bird species in the Top End and is sometimes referred to as Drop Lorri Syndrome.

In the past week, suburban Darwin animal hospital The Ark has received a spike in lorikeet inpatients — more than 30 in total — all with similar symptoms.

"They're all in a very depressed state," vet nurse Mandy Hall said.

"They are behaving in a way where they cannot control their body [in] a state of drunkenness really, it appears.

"People are finding them walking around in their gardens and on roads. They're also being mistaken for pet birds because they have no fear response. They are just easily preyed upon."

Mandy Hall with a sick lorikeet that will likely be euthanased. ( 105.7 ABC Darwin: Emilia Terzon )

On Tuesday morning, Ms Hall had three lorikeet patients, one of which was not moving or responding to food and was close to needing to be euthanased.

"Some of them have been OK with very minor symptoms and we've sent them to wildlife carers," she said.

"Some of them come in extremely unwell and have to be put to sleep, and others just die."

'Sleepy' but not actually on a bender

In previous years the appearance of the confused and stumbling lorikeets had seen conclusions that the birds were intoxicated from eating fermented fruit.

"[Over] a few days, it is a full-on bender and they can actually die of it," a Parks and Wildlife spokesperson told the ABC in 2010.

But Ms Hall said blood-alcohol concentration tests on the hospital's dead birds had come back with zero alcohol readings.

"Their demeanour is acting like they're drunk or hungover but it's a neurological disorder," she said.

"It's some kind of brain damage affecting motor function."

Ms Hall said tests conducted by government laboratories in previous years had never come back entirely conclusive however had pointed to a virus rather than drunkenness.

Dead lorikeets are being sent off to a Darwin laboratory for testing. ( 105.7 ABC Darwin: Emilia Terzon )

This year The Ark will send at least nine samples to the lab — including the bodies of dead birds — and Ms Hall hoped they would finally get to the bottom of the mystery illness.

"It could be something they're eating that's flowering [at this time of year] like a toxic plant," she said.

"I doubt very much that across the entire Darwin suburbs and rural areas [where they've been found] that it could be a chemical."

Last year The Ark's owner Dr Stephen Cutter told local media that the ailment could be a combination of many factors.

"It may be several different diseases working together, definitely some kind of virus that seems to attack the immune system and usually seasonal," he said.

Ms Hall said finding out what was really wrong with the birds would help with treatment options "and stop this happening every year".

It could also eliminate the possibility of a virus with potential to infect other bird species or even humans.

Ms Hall urged members of the public to pick up any lorikeets with drunk symptoms and bring them into their closest animal hospital in a pillowcase or box.