Date of Award

2003

Degree Type

Thesis

Degree Name

Master of Science

School

School of Natural Sciences

Faculty

Faculty of Communications, Health and Science

First Advisor

Professor Harry Recher

Abstract

This study examined the foraging ecology and habitat selection of the Western Yellow Robin in Wandoo Woodland at Dryandra Woodland, Western Australia. The foraging ecology component was comprised of an examination of foraging behaviour, perch-use selection and pounce-site characteristics. The habitat selection component was comprised of an examination of habitat characteristics of site occupancy and general nesting ecology. The implications of current management at Dryandra Woodland to the ecology of the Western Yellow Robin are discussed in reference to the findings of the present study. Ground-pouncing was the dominant foraging behaviour throughout all seasons, with dead branches of live subcanopy Wandoo trees (Eucalyptus wandoo) and dead fallen timber as the dominant perch substrate throughout all seasons. However, interseasonal shifts were detected, exemplified by a decrease in proportion of ground pouncing, and an increase in foraging height and perching height during the warmer months. These results reflect seasonal changes in foraging behaviour influenced by the seasonality of invertebrate prey abundance, with lower abundance of leaf litter invertebrates and increased abundance of flying invertebrates in warmer months. Intraseasonal shifts in foraging behaviour reflect climatic differences between years. Pounce site characteristics showed selection at multiple spatial scales. At the microhabitat scale, pounce sites had significantly more leaf litter and log material, and less bare ground than random points. At the macrohabitat scale, the distance of pounce sites to logs was significantly less than expected. Associations between foraging sites and logs represents selection for sites with a greater abundance of invertebrate prey associated with dead fallen timber. This pattern of selection is consistent throughout the year, indicating characteristics of ground pounce foraging locations remain the same year round regardless of the shift in foraging behaviours. The habitat selection component of the study showed that sites occupied by Western Yellow Robins had higher canopy density, higher leaf litter and log density, higher proportions of Wandoo trees and Gastrolobium plants and higher fragment coefficients (indicating occupation of sites away from the woodland/agricultural ecotone). These results reflect selection of variables at multiple spatial scales; namely, selection for sites with abundant invertebrate prey habitat (microhabitat scale), selection for highly productive habitat (macrohabitat scale), and selection for sites with a reduced edge effect (landscape scale). Nest site characteristics showed selection at specific spatial scales. Although nest sites were located at a variety of heights, they were largely associated with the basal crown height of trees, affording them relatively unobstructed views of the ground to spot potential predators. Nesting trees were similar in height to surrounding trees, although nesting trees were almost always shorter than the highest of the surrounding trees. At a macrohabitat scale, habitat surrounding nest sites was no different to habitat at non-nest sites, indicating no selection for nest site habitat measured. Territory boundaries varied spatially and temporally, with a contraction of territory boundaries during the breeding season. Nests were normally located with the vicinity of the centre of the breeding territory. The present study indicates the strong association of the Western Yellow Robin with the ground environment, with selection for dense leaf litter and logs at numerous spatial scales. The current Dryandra Management Plan strategies have the potential to detrimentally alter the ground environment on which the resource requirements of the Western Yellow Robins revolve. The impact of the proposed changes in land tenure of Dryandra Woodland to National Park would result in additional human pressure on the environment. The impact of an influx in weed invasion, introduction of the Phytophthora dieback fungus and vehicle disturbance by an increase in visitors, has the potential to detrimentally alter the ecology of the habitats occupied by Western Yellow Robins. Furthermore, the implementation of the current fire management plan and the push for tourism development has the potential to internally fragment Dryandra Woodland to the detriment of the Western Yellow Robin. Future research needs to examine reasons for the continued decline in the distribution and abundance of the Western Yellow Robin in the wheatbelt. Such research should be undertaken at the landscape scale, by examining the effects of agricultural practices on the ecology of the species, such as the effect of remnant area, habitat loss, habitat fragmentation and isolation, grazing, weed invasion, altered ecosystem processes and inappropriate fire regimes. Research should also be undertaken on the impact of agricultural practices on the ground invertebrates of remnant native vegetation of the wheatbelt, as many of the above effects of agricultural practices has the potential to greatly disturb the ground environment. Such disturbance has the potential to alter the abundance of ground invertebrates; an important foraging resource of the Western Yellow Robin.

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