Updated May 20, 2017 10:16:39

Photo: Half of nest boxes are used by possums or non-native rats, not the animals they were set up to help. (Supplied: Mason Crane)

A review of a $200,000 effort to protect animals impacted by a major roadworks project in southern NSW has found its attempts to assist the survival of threatened species have failed.

Researchers spent four years assessing the Southern Hume Highway Duplication project's effectiveness in helping three species affected by land clearing between Holbrook and Coolac.

Australian National University Professor David Lindenmayer said the assessment found that the project failed.

"There will be some populations of these species that basically won't do well now because they won't have the nesting resources and they won't have those resources for the next 200 to 300 years," Professor Lindenmayer said.

"We need to make sure we don't make those mistakes again."

The study, published in the journal Biological Conservation, looked at 587 boxes designed to attract the superb parrot, the brown treecreeper and the squirrel glider — animals considered threatened or in need of assistance as a result of tree clearing.

Photo: Researchers conducted 3,000 checks of nest boxes along the Hume Highway in southern NSW. (Supplied: Daniel Florance)

The study found no evidence that the boxes had been used by the superb parrot and on only seven occasions where utilised by the other target animals, across 3,000 checks.

About 8 per cent of boxes had fallen from their tree.

"Given that trees are usually 80 to 120 years old before they form tree hollows, it is fair to assume that most of the nest boxes would fail before any replacement plantings could provide a suitable habitat," Professor Lindenmayer said.

The Southern Hume Highway Duplication project has been estimated to have cost the Federal Government $800 million.

Part of the environmental conditions included installing a nest box for each of the 587 hollow trees felled in the roadworks.

NSW Roads and Maritime Services (RMS) commissioned both the nesting boxes and the study of their effectiveness.

It said the success of nest boxes would depend on a range of factors including the number of natural hollows nearby, the rarity of the target species, competition from more common species and the design of the nests.

"The project to duplicate the Hume Highway, including between Coolac and Holbrook, complied with NSW and Australian Government environmental conditions of approval," the RMS said in a statement.

Photo: The Hume Highway near Tarcutta during a community inspection in 2011. (Supplied: NSW RMS)

One of the report's co-authors, University of Queensland Postdoctoral Research Fellow Megan Evans, believes the compliance requirement was part of the problem.

"To satisfy the conditions of the offset, the proponent only had to erect the nest boxes even if they completely failed to provide habitat for threatened species," Ms Evans said.

RMS said it will take the results into account when planning future environmental offsets.

Topics: environmental-impact, road-transport, holbrook-2644, tarcutta-2652, coolac-2727

First posted May 19, 2017 12:18:50