Researchers find key role of predatory arthropods in nutrient availability on islands

ResearchEcology lab member Luke Halpin led a recent paper in The American Naturalist, documenting the importance of a large predacious arthropod's habits in structuring trophic dynamics on isolated Phillip Island in the Norfolk Islands Group.

Though Phillip Island Centipedes are now relatively abundant, they were extremely rare in the 1980s due to habitat degradation by introduced pigs, goats, and rabbits. After recording previously undescribed instances of black-winged petrel nestlings falling prey to Phillip Island centipedes, Luke and Honours student Daniel Terrington investigated their diet and foraging activity, discovering that these predatory arthropods likely play an important role in the Phillip Island food web because of their highly varied diet. Not only do these centipedes prey on and consume between 2,109 and 3,724 black-winged petrel nestlings each year, they also consume crickets, geckos, skinks, and even fish dropped from black noddy nests.

Phillip Island centipedes occupy an important ecological niche that might otherwise have been occupied by mammalian predators, as is the case with many island ecosystems that are depauperate of mammals. By preying on a variety of vertebrates Phillip Island centipedes likely make available and distribute marine derived nutrients that would otherwise be unavailable in this system.

“Because of the centipede’s role in driving nutrient transfer, areas of the island with higher densities of centipedes might recover faster than areas that are degraded,” explains Luke. “This could be important for recovery of a variety of critically endangered species on Phillip Island, many of which are endemic and found nowhere else on Earth.”

Despite the fact the centipedes are the main cause of nesting failure for black-winged petrels, the petrel population continues to grow and appears resilient to centipede predation. This, however, does raise the prospect for conservation concerns elsewhere, as innovative approaches may be necessary in disturbed systems where predatory arthropods may interact with prey of conservation importance.

Photo by Luke Halpin. Please note that there is some perspective distortion in this photo. 

Rodent Management Work on Norfolk Island Recognized by Ecological Impact Award 2021

Research Ecology Lab group member Allie Nance, along with Mel Wilson from Norfolk Island National Park (NINP) team have been awarded this year’s Ecological Impact Award for rodent management work on Norfolk Island. Allie’s research has shed light on the above-ground activities of invasive rodents, which are a key threat to endemic species of Norfolk Island.

Standard rodent control measures, which have had few changes since their establishment in 1993, have focused on ground-level baiting. “Rodent control has been happening on the island here for such a long time, but it had gotten to a state where it wasn’t working anymore,” says NINP Natural Resource Manager Mel Wilson.

After discovering that rodents were just as active in the mid-storey and canopy of forests as they were on the ground, Allie’s team went on to test several different and innovative rodent management designs. Baited arboreal tunnels showed a 60% increase in bait uptake by rodents, and experimental tree-mounted lethal rodent traps removed 19 rodents from the population over a month, with no signs of harming non-target species.

These new insights will inform the Norfolk Island Threatened Species Recovery Plan, which is currently undergoing review.

“Our work happened at the perfect time when we could push to implement a change. I think it’s going to make a big difference,” says Allie Nance.

Allie Nance and Mel Wilson will co-present a plenary at the forthcoming Ecological Society of Australia Conference in November.

Photo by Nick Wiggins

Experts flown into remote area to save rare bird species ahead of bushfire

Dr Rohan Clarke, and Dr Rowan Mott from the ResearchEcology lab were recently deployed to Howe Flat (east of Mallacoota) to lead the capture of 15  of the ~160 Endangered Eastern Bristlebirds that remain in Victoria. This unprecedented action was undertaken to ensure an insurance population was safely held away from the fires that have devastated much of eastern Victoria and NSW. Along with their project partners (from Zoos Victoria, DELWP, Parks Victoria, University of Wollongong, Currumbin Wildlife Sanctuary), and supported by first class logistics teams (Fisheries Victoria, The Australian Defence Force in Partnership with Singapore Defence Force, and the Orbost Incident Control Centre), Rohan and Rowan were flown in via Chinook Helicopter and got to work.

"There were literally aircraft water-bombing the fire only a couple of kilometres away while we were working," Dr Clarke said. "It [the fire] was incredibly close; it burnt into the northern edge of the heath where the bristlebirds live."

“We were able to catch 15 birds and move them to Melbourne Zoo – an insurance population should the remaining birds at Howe Flat be wiped out by fire”, said Dr Mott.

"The fire is still really active. We can't put them back until the fire is completely out," Dr Clarke said. "Hopefully this insurance population wasn't needed, if we haven't lost the site. If the fire burns and get worse, fortunately we have this insurance population."

For a full report, see: https://www.abc.net.au/news/2020-02-28/bristlebirds-rescued-in-chinook-mercy-dash-during-bushfires/12001212

Photo by Tony Mitchell