• Researchers on World Heritage-listed island to examine rodent eradication program’s impact on Lord Howe Currawong
• Threatened species requires protection during baiting program

A team of Charles Sturt University (Charles Sturt) researchers are in the final stages of a years-long stint on Lord Howe Island collecting data for a study on one of the World Heritage-listed site’s threatened bird species.

Charles Sturt researchers Dr Melanie Massaro, Dr Rachel Whitsed and PhD candidate Richard Segal are investigating the effects of a rodent eradication program on the Lord Howe Currawong.

The trio are usually based at the Charles Sturt Institute for Land, Water and Society (ILWS) research centre in Albury-Wodonga.

But over the past two years, Dr Massaro and Mr Segal have collected data on the currawong’s survival, nesting success, habitat use, and diet, to be used in comparison to information obtained at the eradication program’s conclusion.

In May, Dr Massaro returned to the island - some 586 kilometres off the coast of Port Macquarie – at the invitation of Acting Chief Scientist of the Science Division of the NSW Office of Environment and Heritage Mr Nicholas Carlile.

Their brief was simple: to help safeguard currawongs in aviaries while the rodent eradication program continued.

“Because currawongs are omnivores and they forage on fruit, insects, other birds and rodents, there is a risk of losing some to secondary poisoning,” Dr Massaro explained.

“However, the risk to currawongs is small because the rat and mouse bait used during the eradication is slow acting, and rodents that have taken the bait usually retreat into their burrows where currawongs can’t access them.”

Nevertheless, 50 per cent of the island’s currawongs – or 120 birds - were captured and placed in the care of staff from Taronga Zoo, while the threat of poisoning to some of the island’s other fauna necessitated their capture as well.

“The endangered Lord Howe woodhens are more likely to pick up the rodent bait and this is why over 95 per cent of the island’s population were also caught and put into captivity,” Dr Massaro said.

The Lord Howe Currawongs are easy to track and identify, even on an individual basis.

“The majority of currawongs on the island are uniquely colour banded, which allows us to recognise individual birds from a distance,” Dr Massaro said.

“We can study their survival before and after the rodent eradication and how they may change their nesting and foraging behaviours over time.”

The rodent eradication program will finish at the end of July, with the birds to be released from captivity once it is deemed safe to do so.

Dr Massaro, Mr Segal and a field assistant will return to Lord Howe Island in October, where they expect the volume of weeds to have increased.

Dr Massaro said one of the concerns held by the Lord Howe Island Board - a statutory authority responsible to the NSW Minister for the Environment - is whether the currawongs are spreading invasive weeds such as cherry guava by eating the fruit and then regurgitating the seeds they can’t digest.

Therefore Mr Segal, who will stay on the island for three months, will also conduct a germination experiment in the island’s nursery to study the seeds contained in the currawong’s regurgitations.

Courtesy of a fellowship issued by the office of the Deputy Vice-Chancellor (Research, Development and Industry), and funding secured from the Australia and Pacific Science Foundation, Dr Massaro will be able to continue the project for another year and return to the island in 2020 as well.

Running concurrently is a second project, a phylogenetic study of the currawongs with collaborators Associate Professor Bruce Robertson and Mrs Fiona Robertson from the University of Otago in New Zealand.

In October, Professor and Mrs Robertson went to Lord Howe Island for 10 days to work with Dr Massaro to capture and obtain blood samples from about 50 currawongs, which were then released back into the wild.

About half of each blood sample is used to provide base-line data about the currawong’s diet prior to the rodent eradication program, while the other half is used for a phylogenetic study, which examines the evolutionary relationships among biological entities, like species, individuals or genes.

“We think that the Lord Howe Currawong may be a separate species, rather than a sub-species of the Pied Currawong found on the mainland of Australia,” Dr Massaro said.

“But more sampling of mainland birds and analyses of genetic samples is needed to confirm our hunch.”