The loss of habitat remains one of the greatest threats to the conservation of biodiversity globally and many transport projects clear vegetation that wildlife use for food, shelter or movement. The most effective approach to restore habitat loss is sometimes uncertain and we risk implementing strategies that do not deliver the outcomes required. In these situations, projects should test the effectiveness of current best-practice and simultaneously develop innovative techniques that improve best-practice standards. The Echuca-Moama Bridge project in south-eastern Australia involved the clearing of thousands of trees, including 158 large trees with hollows. The project area supports several threatened species, including the Squirrel Glider Petaurus norfolcensis and woodland birds, as well as dozens of common species that all rely on tree hollows for shelter and raising of young. Once tree loss has been minimised as far as possible, the standard approach to mitigate the removal of tree hollows is to install ply-wood nest boxes in nearby trees. However, recent studies have shown wooden nest boxes are colder in winter and hotter in summer than natural tree hollows, placing significant thermal stress on animals. In addition, nest boxes have high rates of decay and collapse, resulting in a net loss of tree hollows over time. In this project, we collaborated with Major Road Projects Victoria to test new approaches to replacing hollows while achieving the approval conditions of the project. The project has a scientifically robust experimental study design with four types of hollows installed in clusters, allowing strong inference to be drawn on the cost and effectiveness of each approach. Each cluster includes one ply-wood nest box, one salvaged log hollow and one hollow carved into a standing tree with a chainsaw, as well as an existing natural hollow, selected to provide an important baseline comparison. Each hollow is installed on a different tree, and all hollows within a cluster are ~25 m apart, and each cluster is ~ 100 m apart. There are a total of 158 clusters, comprising the total number of large trees removed on this road project. The use and condition of each hollow will be monitored for five years, as well as the health and condition of the host tree. The results of the first four years of monitoring will be presented, as well as insights into important aspects of study design and applying this approach to different impacts on transport projects.
