About the Catchment Area : Animals

Revegetating waterways to enhance bird habitat
Re-vegetation of waterways with native plant species has "more positive impacts than negative" according to Richard Day.

That finding is based on a study of the impact of revegetation projects on bird populations by Mr Day, an honours graduate from The University of Adelaide.

The research project, which was funded by the Torrens and Onkaparinga Catchment Water Management Boards, has produced the first quantitative evidence in Australia that riparian restoration is having a positive overall impact on bird biodiversity.

Riparian restoration, which involves the removal of exotic deciduous trees such as willows, ash, elm and poplar, the control of woody weeds such as blackberry, gorse, broom and briar, and revegetation using native plants, is a major element of the Catchment Water Management Boards' watercourse management program. Such work is intended to stabilise water courses, improve water quality and enhance biodiversity.

During the study, Mr Day monitored bird populations at 14 sites in the Mt Lofty Ranges. He found a third of the 68 species recorded in the survey increased significantly following clearing of exotic vegetation or after revegetation, with revegetation having a positive impact on at least 15 species. Only 3 species decreased significantly.

The numbers of three species - silvereye, blackbird and Adelaide rosella - decreased in abundance following clearing, and then increased when the native vegetation became established.

Three other species - galah, magpie and magpie lark - increased following willow removal but their populations fell again when the native vegetation became established. However, all of these species are widespread and generally increasing in abundance, and are of no conservation concern.

Another three - grey fantail, white browed scrubwren and golden whistler - fell when willows, the species on which Mr Day concentrated in the study, were removed, and did not increase with re-vegetation. While this was a less than desirable response to restoration, their numbers may well recover as the native vegetation matures.

The findings indicated that different stages of the revegetation process impact differently on the different bird species. “This highlights the fact that different types of birds require different habitats”, Mr Day said.

Species disadvantaged by willow removal were mainly small insect-eating species which forage in or under dense vegetation or on the leaves and branches of trees and shrubs.

Aerial insect-eaters, water birds, reed-dwellers and open-habitat feeders all appeared to benefit from the open spaces created by removal of willows and similar vegetation.

Birds that feed primarily in open areas were also more prolific in cleared sites but when the replanted native vegetation started to "fill in" some of the open space, conditions changed again in favour of nectar-feeders and some specialised insect-eaters.

It is important to remember that the species of birds found in areas of exotic trees are not necessarily the species that would have originally been present prior to the invasion of those exotic species.

Mr Day's findings point to the need for a sensitive approach to landscape restoration.

Information kindly provided by Richard Day and prepared by Graeme Jennings for Jon Lamb Communications