Doctor of Philosophy
Baker, Jack, Ecotones and fire and the conservation of the endangered eastern bristlebird, Doctor of Philosophy thesis, , University of Wollongong, 1998. https://ro.uow.edu.au/theses/2090
Conserving Australia's rich biodiversity should begin with a concern for individual species. This thesis explores the issues of threatened species status, fire as a threatening process and the significance of bird habitat at ecotones, with a focus on the eastern bristlebird as a case study. The dominant issue of ecotones is explored in relation to bird populations and heath-wood edges.
The biological status of the eastern bristlebird was clear by 1997. It was estimated that there were fewer than 2 000 individuals occupying less than 120 km2 . Their range covered 1 400 km from Conondale Range, south-eastern Queensland, to Croajingolong in north-eastern Victoria. They were confined to three disjunct regions. The 6-9 northern populations were on the brink of regional extinction. There was one small widely spread southern population at Nadgee-Croajingolong. The central populations were contained in two main areas, Barren Grounds-Budderoo and Bherwerre Peninsula, Jervis Bay, with possibly a few small fragments at Morton-Red Rocks. The fragmentation and decline that were probably ongoing for millennia, have apparently been hastened by European settlement.
The legal status of the eastern bristlebird is currently (1998) Endangered in Queensland (Nature Conservation (Wildlife) Regulation 1994 of the Nature Conservation Act 1992), Endangered in NSW (Final Determination under the NSW Threatened Species Conservation Act 1995, gazetted 31 January 1997 ), Endangered in Victoria (Flora and Fauna Guarantee Act 1988 as amended (CNR 1995)) and Endangered nationally (Endangered Species Protection Act 1992 as amended 1 June 1998).
Fire has been a feature of eastern bristlebird habitat in the regions where the species currently occurs. This thesis documents evidence to suggest that fire has caused the loss of populations in prehistoric, historic and recent times. By contrast, at Barren Grounds, in the absence of fire during 1992-7, the population almost doubled. There was a short to medium-term trend of density increasing from zero or low density immediately after fire, recovering to a plateau of approximately 2 birds per 5 ha, 10 years after fire. There was some evidence that the extent of a fire and the availability of fire refugia are important factors in the recovery of populations after fire. Eastern bristlebirds can occur and breed in relatively long-unburnt habitat, for example, at Nadgee, in habitat with fire-age older than 24 years.
Two central theories have emerged from the concept of ecotones: "the edge effect" and "ecotonal species" (Odum 1958). Few studies have explored these concepts at natural edges between two contrasting vegetation communities. In the last decade, the eastern bristlebird has been called an ecotonal species, although Bramwell et al. (1992) have provided the only analytical test of this assertion. In the present thesis, bird populations across heath-wood edges were studied for evidence of edge effects and ecotonal species. When the ecotone was taken as a 50 m wide zone across the edge, there was no evidence for greater bird abundance or species richness at the ecotone. Rather, the general pattern was that the ecotone and the wood were similar and they had double the bird abundance and richness of the heath. There was an underlying pattern that the abundance and richness for the wood side of the edge were greatest at the ecotone and similarly the values for the heath side were greatest at the ecotone. However, this pattern was statistically significant only in one case. Bird abundance at the wood side of the ecotone was approximately 67% greater than in the wood. This was the strongest piece of evidence in the present study for the dogma of edge effect.
Bird species were categorized by Sisk and Margules (1993) according to whether they avoided or exploited habitat at edges between contrasting vegetation communities. I adapted their response models to describe the localized distribution patterns of the abundant species found across heath-wood edges. For 20 species, 45% fitted the model for ecotone ignorers, 35% fitted the model for ecotone exploiters and 20% fitted the model for ecotone avoiders. However, the pattern of specialization of bird species for the habitat on either side of the edge was more pronounced than the pattern of response to the ecotone. The eastern bristlebird fitted the model for a habitat generalist - ecotone exploiter but it was not restricted to the ecotone. There were no entirely ecotonal species at the heath-wood edges at Budderoo-Barren Grounds, Jervis Bay or Nadgee.
Past and present records show that the eastern bristlebird has been associated with most major vegetation communities in wetter parts of south-eastern Australia. Dense low cover was characteristic of all historic and recent eastern bristlebird habitat descriptions. This factor is common throughout the species' range in the various vegetation communities it inhabits. At Barren Grounds, layers of ground cover, low cover and tall shrub cover were shown to be important features which distinguished eastern bristlebird habitat from areas where bristlebirds were not detected. The species is often associated with heathland or heathy vegetation, however, its habitat specialization is not heath, it is dense low vegetation.
Vegetation structure was studied across heath-wood edges. There was no evidence for an overall pattern or even a single site where substantial areas of heath ecotone and wood ecotone had a vegetation structure different to that of the heath or the wood. The most usual pattern of vegetation structure at the ecotone was a simple grading from a highly uniform heath to a less uniform wood. Heath ecotone grouped most closely with heath and wood ecotone grouped most closely with wood.
The eastern bristlebird is a cryptic species. Individuals were radio-tracked in a detailed study of the species in its habitat at Jervis Bay and useful tracking data were obtained for 20 birds. Home range areas were estimated using minimum convex polygons and averaged 4 ha (range 1.5-6.6 ha) for one week (7 birds) and ≥ 10 ha for 2-6 weeks (2 birds).
The radio-tracking results supported previous studies which indicated that, at Jervis Bay, eastern bristlebird occur in a wide variety of habitats with relatively high densities in some areas. The highest density was 8 birds in 19 ha (2.1/5 ha) during May 1997. For the Jervis Bay population, the density estimates calculated using aural survey data were very similar to those calculated using radio-tracked birds. This result placed confidence in the validity of the aural surveys in all areas.
The tracking data for six birds at each of two heathland edge sites were investigated for habitat selection and edge affinity. Overall, there was significant selection by the birds among the habitat zones of heath, wood and the 50 m wide ecotone. However, individual birds varied in their preference and avoidance of these three habitats. Overall, the birds showed no attraction towards heath-wood edges.
The legal status of the eastern bristlebird has been changed during the past decade from Vulnerable to the more appropriate category of Endangered. This has happened in all states where the species occurs (Queensland, NSW and Victoria) and nationally, in recognition of its historic decline and current biological status.
This thesis concludes that the eastern bristlebird is cover-dependent and fire-sensitive more a habitat generalist than a heath-wood ecotone exploiter. The existing larger eastern bristlebird populations (Barren Grounds-Budderoo, Jervis Bay and possibly Nadgee- Croajingolong) would probably grow and expand their local area of occupancy if they were protected from disturbance, particularly fire which kills individuals and removes the dense low vegetation in their habitat. Recovery planning for the eastern bristlebird requires not only strategies to increase the number of individuals but also strategies to rebuild or re-establish populations outside Barren Grounds-Budderoo, Bherwerre Peninsula and Nadgee-Croajingolong. Ku-ring-gai, Woronora Plateau, Morton and Beecroft Peninsula were suggested as possible translocation sites.
The management of fire in eastern bristlebird habitat is an important issue. The most sensible way to manage eastern bristlebird habitat would be to exclude fire unless site-Peninsula and Nadgee-Croajingolong. Ku-ring-gai, Woronora Plateau, Morton and Beecroft Peninsula were suggested as possible translocation sites.
The management of fire in eastern bristlebird habitat is an important issue. The most sensible way to manage eastern bristlebird habitat would be to exclude fire unless sitespecific population monitoring data demonstrate that this is detrimental. Management plans need to identify areas of eastern bristlebird habitat and develop strategies for protecting them from fire. Suggested strategies are slashing rather than prescription burning to create fuel-reduction zones, planning escape routes for eastern brisdebirds when prescription burns are used and aerial water-bombing to protect habitat when fires are out of control.
Individual eastern bristlebirds have a relatively large home range, overlapping home ranges and a considerable daily range. This implies that disturbances in the vicinity of eastern bristlebird habitat, such as vehicular traffic within 500 m , are likely to have an impact on a large proportion of the existing populations because these populations currently occupy relatively small areas.
This thesis concludes by suggesting that the management of threatened species recovery and biodiversity generally could benefit from an accountable administration concerned with species as a whole and biomes, whose assessment criteria should be improvements in conservation. Management at the local level should deal with populations "on the ground" through adaptive management rather than by prescription. The key to adaptive management is communication between researchers and managers and within the levels of management. Numerous research questions have arisen out of m y studies. However, the fundamental tool of conservation management remains population and habitat monitoring.