Effects of surrounding land use change on nesting success of small-bodied birds in Eucalyptus woodland remnants
Date
2020
Authors
Okada, Sachiko
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Land has been extensively modified in response to human needs for thousands of years. In recent times, the change in land use from agricultural areas to tree plantations has been expanding worldwide to satisfy the increasing demands for wood/paper products. In Australia, some areas of cleared agricultural land have been transformed into exotic pine plantations, particularly in New South Wales (NSW). Species occurring in fragments of remnant native vegetation, including birds, may be influenced by the effects of new forms of surrounding land use dominated by exotic Radiata Pine (Pinus radiata) plantations.
In this thesis, I sought to quantify how the transformation of landscapes from grazing land to exotic pine plantations influenced the breeding success of small-bodied birds in woodland remnants. I also sought to determine if the results from artificial nests were broadly consistent with those obtained from natural nests. To achieve these aims, I conducted a series of studies of natural and artificial nests in the Nanangroe State Forest and in the surrounding private farmlands in south-eastern NSW, Australia. My study sites were Eucalyptus woodland remnants surrounded by one of two types of matrix; grazing land or maturing stands of Radiata pine plantation.
In the natural nest study (Chapter 2), I found significantly fewer nests in woodland remnants surrounded by the plantation than in woodland remnants located in farmland. The proportion of nests of generalist avian nest predators was significantly higher in woodland remnants surrounded by the plantation, compared to woodland remnants surrounded by farmland. In general, I found that breeding success of birds with a larger mean body mass was higher than small-bodied birds, and small-bodied birds reproduced more successfully at a lower nest height. Notably, nesting activity of some forest taxa, including species of conservation concern, was observed both in woodland remnants surrounded by the plantation and in the plantation matrix.
In experiments using two types of artificial nests (Chapter 3), I found the following patterns. (1) The majority of nest predators were birds. (2) There were higher levels of nest predation in woodland remnants surrounded by the plantation than in woodland remnants located within farmland, with cup nests being inferior to domed nests against nest predation in the both landscape contexts, and (3) Both natural and artificial nests were more susceptible to nest predation in woodland remnants surrounded by the plantation than in woodland remnants located within grazing paddocks.
Overall, my research has shown that land use change from grazing areas to exotic pine plantations may provide more habitats for small-bodied forest species including the Flame Robin (Petroica phoenicea), a vulnerable species in NSW. Conversely, landscape transformation may reduce the amount of habitat for ground-foraging small-bodied woodland birds, such as the Brown Treecreeper (Climacteris picumnus victoriae) and Dusky Woodswallow (Artamus cyanopterus), which are also vulnerable in NSW. Conservation of small-bodied forest versus woodland taxa may require different kinds of management within plantations. However, retaining woodland remnants within the boundaries of plantations benefits a range of kinds of native birds, including forest and woodland taxa.
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