ABC Catalyst: Dr Dejan Stojanovic describes how hollows are coveted resources for generations of different animals

Thursday 22 October 2015

This tree-hollow is one of a very very rare cohort of resources in this forest

Tree Hollow

Dr Dejan Stojanovic tells Catalyst's Mark Horstman, hollows are coveted resources for many generations of different animals. This one was felled by wildfire.  Link to ABC CATALYST  Video: ABC Catalyst: Dr Dejan Stojanovic describes how hollows are coveted resources for generations of different animals. (ABC News)

Part of the ABC Catalyst Program

Lethal traps 'might offer solution' to threat to swift parrots from sugar glider

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Researchers trying to save endangered swift parrots from extinction say lethal possum traps to control predatory sugar gliders "might offer a solution".

Dr Dejan Stojanovic and his team from the Australian National University (ANU) recently discovered that sugar gliders were eating approximately half of the adult female swift parrots that nest in mainland Tasmania every year, as well as their eggs and chicks.

The team is working in eastern Tasmania — the only place in the world where swift parrots breed.

Genetic evidence confirms that sugar gliders were introduced to Tasmania from mainland Australia within the last 200 years.

To protect individual parrot nests in glider-infested areas, Dr Stojanovic is trialling lethal traps to humanely cull sugar gliders, similar to those used to control feral brushtail possums in New Zealand.

"The swift parrot population appears to be in freefall, and as a conservation biologist I have two options," he said.

"I can continue to monitor them into extinction and do nothing, or we can investigate techniques that might work, may not necessarily be palatable to everybody, but might offer a solution to prevent the extinction of one of Australia's most iconic species."

Swift parrots and sugar gliders battle for forest hollows

The entire global population of swift parrots, estimated at about 1,000 pairs, migrates to Tasmania to breed during the summer and feed on flowering blue gums and black gums.

State and federal governments have been unable to arrest the decline of swift parrots, as their nesting hollows in old growth trees are being lost to industrial logging, land clearing, wildfires and firewood harvesting.

Conservation biologists believe that the "bizarre threat" of sugar gliders to swift parrots is an unexpected knock-on effect of this habitat loss.

"It's in places where the best glider habitat happens to overlap with the best swift parrot habitat that these birds are at most risk," Dr Stojanovic said.

Sugar gliders also nest in hollows and are known to be opportunistic omnivores, but it remains unclear why they have developed such a taste for swift parrots.

The scientists believe that the loss of breeding habitat forces sugar gliders and swift parrots into greater competition for nesting sites, exacerbating the predation pressure.

"In years where the flowering draws parrots into places already occupied by gliders, this can act as a trap for these birds, which settle in these areas and then all end up eaten," said Dr Stojanovic.

"Based on our models of population viability of the swift parrot, that rate of predation by sugar gliders on the nesting females is likely to lead to a population collapse of up to 95 per cent within three generations."

Three generations of swift parrots means only 16 years before the species is functionally extinct in the wild.

"To be listed as critically endangered under the international legislation, you need an 80 per cent rate of decline over three generations," he told Catalyst.

"We've recorded nearly 95 per cent rate of decline, so it's really very severe."

On the brink of being eaten to extinction

The team's research found that the loss of old growth eucalypt forest dramatically increased the risk that endangered swift parrots and their young would be killed by sugar gliders.

"Our models show that in areas where there's a large area of mature forest cover, you've got a much better chance of surviving if you're a swift parrot nest than in an area of very fragmented and disturbed younger forest," Dr Stojanovic said.

"In places where old growth has been reduced to as little as 20 per cent of the available forest cover, predation by gliders can reach 100 per cent, which means every bird dead, every nest fails.

"In areas where the amount of old growth forest cover is higher, survival for swift parrots can be more than 90 per cent."

The good news for swift parrots is that sugar gliders are still absent on islands off mainland Tasmania.

On Bruny Island, east of Hobart, with zero predation by gliders, the survival rate and nesting success of swift parrots is nearly 100 per cent.

However, their habitat on the island remains available for logging, and scientists are concerned that the parrots' survival on glider-free islands cannot be relied on to save the population.

This breeding season, thanks to public donations, scientists are installing 500 nest boxes to provide extra "artificial hollows" and buy time for the swift parrots.

On mainland Tasmania, they intend to use the nest boxes to further their understanding of the interaction between sugar gliders and swift parrots, and help design "glider-proof" boxes.

"We're trying to keep all of our options open because nobody's done this before," said Dr Stojanovic.

"This is a really challenging problem to address."

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