Date of Award

2000

Degree Type

Thesis

Degree Name

Doctor of Philosophy

Faculty

Faculty of Communications, Health and Science

Abstract

Anthropogenic habitat modification is a significant threat to the conservation or global biodiversity. The fragmentation and alteration of woodland habitat has resulted in the substantial decline of many woodland bird species in the agricultural regions of southern Australia. The Rufous Treecreeper Climacteris rufaa, a once common woodland resident, has declined in abundance in the wheatbelt of Western Australia and appears to be sensitive to habitat fragmentation. The reasons for this are unclear because our knowledge of the species and the threats posed by fragmentation arc limited. In this study, I compared the social organisation, habitat selection, reproductive success, dispersal and population dynamics of two Rufous Treecreeper populations living in the Western Australian wheatbelt. The first population occupied a large (8,500 ha), relatively undisturbed and unfragmented landscape. The second occurred in an equivalent sized area that had been substantially modified by agriculture. I hypothesised that habitat fragmentation and alteration would adversely affect the viability of the population living in the agricultural landscape. In the unfragmented landscape, treecreepers lived in cooperatively breeding, territorial groups. A group usually comprised a primary (assumed to be breeding) male and female, and philopatric offspring (helpers) from previous breeding seasons. Helpers assisted in the feeding and caring of nestlings and there was a positive relationship between group size and reproductive output. Breeding groups often fanned interactive neighbourhoods whereby resident individuals from one territory would feed nestlings in adjacent territories. A total of 77.7% of 148 nesting attempts produced at least one fledgling. Annual productivity per breeding group (n = 90 group years) was 2.1 ± 0.18 fledglings. Fledgling and juvenile survival rates (0.76 ± 0.04 and 0.46 ± 0.03 respectively) were comparatively high, as was the annual survival rate of primary males (0.77 ± 0.06) and females (0.75 ± 0.05). A multi-scaled analysis of habitat use in the unfragmented landscape identified preferential habitat selection by the species at three spatial scales. At the landscape scale, treecreepers used Wandoo Eucalyptus wandoo woodland at a significantly higher rate than predicted by the availability of this woodland type. Territory selection was positively correlated with the density of hollow bearing logs and nest sites, and tree age. These structural characteristics were also positively correlated with reproductive success und survival in treecreepers, indicating that habitat structure may be a useful measure of territory quality. Nest sites (hollows) were preferentially used if they had a spout angle of ≥ 50° and an entrance size or 5-10 cm, but nest-site selection was not related to nest success. The ecological traits of the treecreeper population living in the agricultural landscape differed from the population in the unfragmented area in a number of ways. Habitat fragmentation in the agricultural landscape disrupted territory contiguity with adverse consequences for social interaction. Nest success and annual productivity were significantly lower in the agricultural landscape, although they varied between different categories of habitat remnants. Reproductive success was lowest in grazed remnants supporting comparatively high population densities. Landscape differences in success did not appear to be a result of a disparity in nest predation levels, but may be related to variation in food availability and habitat quality. The spatial structure and dynamics of the subdivided population in the agricultural landscape were consistent with certain aspects of metapopulation theory. Treecreepers lived in spatially discrete local populations that were unlikely to persist without immigration owing to low reproductive and survival rates. However, movement between habitat remnants appeared to be sufficient to rescue these local populations from extinction. Although declining in numbers during the study, the subdivided population in the agricultural landscape appeared to be fluctuating around equilibrium owing to immigration from outside the study area. The consequences of habitat fragmentation for the Rufous Treecreeper are complex and interactive. A reduction in habitat area and an increase in remnant isolation disrupts the social organisation of the species and results in small localised populations that are susceptible to extinction. Modification of the remaining vegetation may reduce habitat quality leading to poor reproductive success. In addition to increasing habitat area and maintaining landscape connectivity, future management of fragmented landscapes must focus on improving the quality of remnant vegetation by removing degrading process and ensuring the recruitment of endemic plant species.

Included in

Ornithology Commons

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