Bird species richness and abundance in wandoo woodland and in tree plantations on farmland at Baker's Hill, Western Australia

Abstract

In this study, bird species richness and abundance in residual wandoo woodland and in revegetated areas were compared at Baker's Hill, Western Australia. Twenty-seven 1-ha sites were censused up to 42 times a year for three years (1995–97). Six sites were located in a large remnant of wandoo woodland, with three having an understorey of Dryandra sessilis, three in road verges, 12 in farmland that had been planted with native trees on a 2 m × 3 m grid in the period 1976–85 and six sites had been planted at an agroforestry density (10 m × 7 m) in the period 1988–91.

In total, 87 bird species were recorded over the three years. Sites in the road verges and wandoo woodland with an understorey that included Dryandra sessilis had a significantly higher total number of species than did sites in wandoo without an understorey of Dryandra sessilis and the agroforestry sites. Sites in reforested farmland had the least species. The differences in species richness were primarily due to fewer passerine species.

The abundance of the 15 commonest passerine species was examined. The abundance of the insectivore species followed the pattern of species richness. Few honeyeaters were found in wandoo woodland without an understorey of Dryandra sessilis, and numbers were low in the reforested sites. Overall, the abundance of honeyeaters was similar in the road verges, wandoo woodland with an understorey and agroforestry sites. Peak abundance occurred in spring and autumn at agroforestry sites and in winter in wandoo woodland sites with an understorey of Dryandra sessilis.

Abundance varied with season for 6 of the 15 species. All the insectivore species had seasonal differences in abundance, with the pattern differing with species, but being the same in all types of vegetation. For the honeyeaters, the patterns differed in the different types of vegetation.

Most of the remaining species occurred either frequently at a few sites or occasionally at either a few or many sites. Changes in the status of species in the Baker's Hill area are documented.

The difference in conservation value for birds of the two types of revegetation is that when there is either a canopy or perching sites within 1 m of the ground, then the abundance of a range of insectivorous species that forage partly or wholly on the ground is higher. As the revegetated sites provided nectar for the honeyeater species in autumn and the Dryandra sessilis did so in winter, nectarivorous birds were present for a longer period of the year. Increased habitat allowed a greater number of species to use the study area.