The organisation is calling for the cancellation of the 2020 season and a moratorium to be placed on future seasons until the drought on the mainland has broken.

Birdlife cited long-term studies into duck numbers in Tasmania to show that mainland ducks are staying for protracted periods, but not breeding here, indicating it is only a temporary location for them.

The pink-eared duck and hardhead are among those most at risk if their numbers decline while in Tasmania.

Birdlife Tasmania convenor Eric Woehler said Australia's ducks are dispersive, meaning they follow abundant water.

"Because Tasmania is wetter than the mainland, they're coming here as a refuge where they're joining waterfowl all around the state where there's water and food to survive," he said.

"At some point in time, these mainland species will return to the mainland to breed when conditions return to some form of normality.

"Even though these mainland species are not on lists of species to be shot, we do know that other species that are barred from being shot are being harmed."

The Tasmanian Bird Report from September 2018 - Birdlife's last comprehensive study of duck numbers in Tasmania - found a peak in mainland ducks in 2003-04, a trough around 2010-12, and another peak after that. It resulted in a conclusion that many species were flying to Tasmania during mainland dry conditions.

IN OTHER NEWS:

Dr Woehler said duck hunting was effectively banned from all states and territories except Tasmania and Victoria. Victoria this week announced a limited duck hunting season.

He said it had never been considered in Tasmania, however.

"It's very hard in this day and age to defend something like duck shooting," Dr Woehler said.

"Ducks are an important part of the ecosystem. In Australia, they don't migrate like ducks in other parts of the world. Instead, they're dispersive and follow the water."

A spokesperson for the Tasmanian Government said "appropriately managed" ducking hunting was a "legitimate recreational activity".

"There are a range of rules and regulations in place as part of ensuring the sustainability of the activity as well as animal welfare requirements," he said.

"As part of the sustainable management of the duck hunting in Tasmania, the open season is for a specific period of time, only certain species are able to be taken, bag limits apply as well as waterfowl identification tests for hunters taking part in the season.

"The Department of Primary Industries, Parks, Water and Environment undertakes monitoring of the harvested species annually using waterfowl counts and by collecting harvest and sample data to help ensure the sustainability of takes."

But Dr Woehler said this monitoring relied on information from farmers and hunters, which could constitute a "conflict of interest".

The 2020 Tasmanian duck hunting season will run from March 7 to June 8.