Banding records indicate that birds are capable of surviving to more than four years of age (Bramwell and Baker 1990; Higgins and Peter 2002) and the longevity of birds that survive to maturity is probably at least six years (Holmes 1998, Baker unpubl. data). The generation length3 is estimated to be five years (Garnett and Crowley 2000).
The Eastern Bristlebird breeds from August to February (Campbell 1900; Chaffer 1954; Morris et al. 1981; Higgins and Peter 2002). Females build a small, globular nest that has a side entrance and is made from grass, bark, sedges or reeds, and sometimes leaves (North 1901-1904; McNamara 1946; Chaffer 1954; Holmes 1989, Higgins and Peter 2002; Booth 2009). The nest is generally constructed at 10 to 45cm above the ground in low dense vegetation, in grass tussocks, sedges, ferns and shrubs (Campbell 1900; North 1901-1904; McNamara 1946; Holmes 1989; Chapman 1999; Baker 2000; Higgins and Peter 2002). Occasionally, nests are built in lower branches of shrubs (Holmes 1998).
Birds in the northern population nest in large living grass tussocks, in clearings not shaded by trees (J. Young unpublished data). In north-eastern NSW in the 2009 breeding season, most nests were located in Poa tussocks, even where other tussock grass species were present (J. Young unpublished data). In previous studies nesting has been observed most frequently in Sorghumleiocladum, and less often in Poa sieberiana, P. labillardieri and Pennisetumalopecuroides (Holmes 1989; Chapman 1999). Birds in the central population nest in grasses, in sedges such as Gymnoschoenus sphaerocephalus, Gahnia spp. and Lepidosperma laterale, and in the rush Leptocarpus tenax (McNamara 1946; Chaffer 1954; Baker 2000; Higgins and Peter 2002). There are no nest data for Howe Flat or Nadgee NR (L Evans and M Bramwell pers. comm. 2010). Table 3 lists the nesting microhabitat recorded for the Eastern Bristlebird (from Baker 2000).
Clutches consist of two or sometimes three eggs (Campbell 1900; North 1901-1904; Chaffer 1954; Holmes 1989; Higgins and Peter 2002). The eggs are creamy-white and speckled with brownish or greyish spots, darker at the blunt end (North 1901-1904; McNamara 1946; Chaffer 1954; Booth 2009). The eggs are incubated by the female bird (Booth 2009), for a period of at least three weeks (Chaffer 1954). The nestlings are fed by both parents (Chapman 1999) during the nestling period of at least 16 days (Chapman 1999; Higgins and Peter 2002). It is thought that pairs probably rear only one brood per season, and that usually only one young is fledged per successful breeding attempt (Chaffer 1954; Holmes 1989, 1998; Baker 1998).
Field studies in southern Queensland by J. Young (unpubl.) have identified that birds can re-clutch following the failure of a first nesting attempt, and in captivity re-laying has occurred in four cases after an average of 17 days since egg removal (Booth 2009). Breeding failure is common. Nest and/or chick desertion is known to occur after human interference (Chaffer 1954; Hartley and Kikkawa 1994), and may also occur after other disturbances such as intrusion by potential predators or storm damage.
Eastern Bristlebirds raised in captivity reach sexual maturity at approximately 317 days (Booth 2009).
Northern populations generally
Usually in grass tussocks Poa spp. or Sorghum leiocladum, away from the shade of trees.
J. Young (unpublished data)
Clarence River near Grafton
Nest of grasses and leaves built in a tuft of rushes near the river
Middle Harbour, Sydney
Nest made of grass, 0.5 m off the ground in a Banksia robur shrub
Five nests 0.15-0.45 m off ground, all in the sedge Gymnoschoenus sphaerocephalus.
Three nests in Gahnia clumps, one was 0.3 m above ground; four nests hidden in grasses; one in a clump of long grass; one nest woven with grasses and some papery (Leptospermum) bark, one 0.9 m above ground.
One nest 0.1 m above ground in dense sedge below 2 m high Leptospermum.
Birdlife Australia nest record scheme
A nest in a clump of Gahnia at the foot of a Melaleuca shrub.
Table 3: Nesting microhabitat of the Eastern Bristlebird (from Baker 2000).
Diet and Foraging Ecology
The Eastern Bristlebird feeds mainly on invertebrates (ants, beetles, flies, cockroaches, bugs (hemipterans), cicadas, grasshoppers, crickets, mantids and caterpillars, but also earthworms and spiders), seeds and small fruits of grasses and other plants including Acacia, Carex, Exocarpos and, possibly, Lyciumferocissimum, but may also take fungi and occasionally nectar from Banksia ericifolia, food scraps and tadpoles (Gould 1865, Lea and Gray 1935; Barker and Vestjens 1990, Holmes 1998; Chapman 1999; Gibson 1999; Gibson and Baker 2004).
Eastern Bristlebirds forage mostly on the ground, where they toss aside leaf litter with their bill, peck food items from the surface and probe into soil, but they do not use their feet to scratch the ground. They occasionally glean food items from foliage or branches, or capture insects in flight (Robertson 1946; Blakers et al. 1984; Hartley and Kikkawa 1994; Baker 1998; Holmes 1998; Chapman 1999; Gibson and Baker 2004).
Hartley and Kikkawa (1994) suggested that drought may impact heavily on bristlebird breeding through a reduction in invertebrates suitable for feeding nestlings.
The Eastern Bristlebird is a sedentary (McNamara 1946; Gibson 1977; Blakers et al. 1984; Holmes 1989; Lamb et al. 1993; Hartley and Kikkawa 1994) or resident (Morris et al. 1981; Cooper 1991) species that undertakes some local movements (Baker 1998; Baker and Clarke 1999) and can recolonise some areas after being displaced by fire (Bramwell and Baker 1990; Hartley and Kikkawa 1994; Jordan 1984; Pyke et al. 1995). The birds are only capable of making weak, low, short-range flights (Chaffer 1954; Holmes 1989; Bramwell and Baker 1990; Lamb et al. 1993; Hartley and Kikkawa 1994; Baker 1998; Chapman 1999), which suggests that dispersal is likely to be mostly through ground movements (Higgins and Peter 2002) and, consequently, that they have a limited ability to disperse (Clarke and Bramwell 1998).
Studies of radio-tagged birds indicate that Eastern Bristlebirds are capable of travelling a total distance of at least 1.5 km during the course of a day (Baker and Clarke 1999). In 2009, Eastern Bristlebirds were recorded two to four kilometres from Howe Flat in heathland where they had previously not been detected, requiring a 2km movement through coastal forest vegetation (M. Bramwell pers. comm. 2010). Translocated birds at Cataract Dam dispersed 5 km in 3 years, and at Beecroft Peninsula a maximum dispersal distance of 6 km was recorded after 6 years (Baker et al. 2012).
The Eastern Bristlebird is territorial during the breeding season and possibly throughout the year (Hartley and Kikkawa 1994; Chapman 1999; Higgins and Peter 2002). The results of one study suggest that the territory is a core-area within the home range that is defended from conspecifics and advertised by loud directional song (Holmes 1989). Territories, some of which are probably permanent (Chapman 1999; Higgins and Peter 2002), range in size from about one to four hectares (McNamara 1946; Holmes 1989; Bramwell and Baker 1990; Hartley and Kikkawa 1994). Home ranges are estimated to be about 10 hectares (Baker 2001).
Population densities within suitable habitat are low compared to those of other heathland birds (Gosper and Baker 1997) with maximum densities of four birds/10ha recorded at Barren Grounds NR (Baker 1998). In the Howe Flat population, 1.5-2 birds/10ha were recorded (Bramwell 2008).
THREATS The main threat to the Eastern Bristlebird is the loss or fragmentation of suitable habitat which can be caused by inappropriate fire regimes and clearing for urban or agricultural development. Habitat loss is recognised as the main process that has reduced the distribution and abundance of the Eastern Bristlebird in the last 150 years. Another potential threat to the species is predation, particularly by feral predators and particularly after fire. Habitat degradation is also a significant threat, particularly in fragmented habitat, and can be caused by disturbance from feral animals (e.g. pigs) and livestock and invasion of weeds. Other potential threats include genetic bottlenecks and inbreeding, climate change and human disturbance (DEC 2004, Garnett and Crowley 2000; Holmes 1998; Stewart 2006).
Historical clearing of coastal heath and escarpment forest is a major reason for the current endangered status of the species. Further loss or degradation of any habitat that supports the Eastern Bristlebird is deemed significant. The possibility of further habitat loss through the application of unsuitable fire regimes and clearance for urban development remains a key threat. “Land Clearance” is listed as a Key Threatening Process under the EPBC Act, including clearance of native vegetation for crops, improved pasture, plantations, gardens, houses, mines, buildings and roads (TSSC 2001a).
While habitat on conservation reserves may be managed for Eastern Bristlebirds, recovery of habitat is not possible in some areas due to current land-zoning for urban development. Protection and management of habitat on private land, particularly for the northern population and at Jervis Bay, is extremely important but challenging as the cumulative impact of residential developments remains a key threat to some local populations.
Clearance or disturbance of habitat due to forestry practices is a threat to individuals or populations on Forests NSW tenure. Forestry activities may cause direct loss of habitat and potential secondary consequences from disturbance and improved access.
The Eastern Bristlebird has little ability to escape fire (ground dwelling, weak flier) and recover afterwards (cover dependant, poor disperser, low fecundity), making it particularly sensitive to certain fire regimes (Smith 1977; Baker 2000; Whelan et al. 2006; Bain et al. 2008). In all populations the species and its habitat are threatened by extensive, intense and/or frequent fires which may cause local extinctions (Gilmour 1983; Baker 1997, 2000; Clarke and Bramwell 1998; DSE 1999). More detail is provided in the Habitat section.
Inappropriate fire regimes can result in indirect or temporary loss of habitat for the Eastern Bristlebird. Post-fire recovery of some habitat may be possible with rehabilitation and/or reintroduction. Much of the known habitat for the species is now reserved so recovery will depend largely on how reserves are managed, but management of habitat and fire on other tenures is particularly important in the Jervis Bay area and the northern population. The aim of fire management in Eastern Bristlebird habitat or former habitat should be to: a) restore important habitat components at degraded sites; and b) maintain important habitat components at occupied sites (Sandpiper Ecological Surveys 2007).
Fire intensity, scale and frequency are all important features to be considered in managing fire in Eastern Bristlebird habitat (see Table 4). Buffer zones and refuge areas are necessary to protect the species from fire and aid its recovery. Feral predator control is another important factor that may influence the re-occupancy of habitat by Eastern Bristlebirds after fire (e.g. Lindenmayer et al. 2009) and is discussed further in the Predation section.
Intensity and scale: Mosaic, low-intensity or small-scale burns to create / maintain unburnt refuge areas. Refuges must be close and accessible to the birds under prevailing fire conditions. Not to be lit on two fronts due to the chance of trapping birds.
Bain et al. (2008); Baker (1997, 2000); Baker et al. (1997); Holmes (1989); Pyke et al. (1995); Sandpiper Ecological Surveys (2007)
Frequency: Ensure fire frequency will maintain suitable habitat for a specific site (too frequent may prevent vegetation from becoming dense enough to be suitable and too infrequent may cause a change in the vegetation community to an unsuitable habitat). Site specific but generally >15 years for central and southern, 4-5 years for northern.
Baker (1997); Hartley and Kikkawa (1994); Sandpiper Ecological Surveys (2000a, 2007); Stewart (2006); D. Stewart pers. comm.. (2012)
Buffers: Create / maintain buffer zones &/or management tracks (to protect habitat from wildfire)
Hartley and Kikkawa (1994)
Seasonality: Cooler weather (autumn, winter) burning to avoid breeding season and maximise regeneration. Not during drought conditions
Hartley and Kikkawa (1994); Sandpiper Ecological Surveys (2007)
Table 4: Fire characteristics important for Eastern Bristlebird habitat Northern Population
There have been several studies on the fire ecology and habitat requirements of the northern population (Holmes 1989, 1997; Lamb et al. 1993; Hartley and Kikkawa 1994; Sandpiper Ecological Surveys 2000a, 2007). Where fire is too infrequent bristlebird habitat is adversely affected and local extinctions are likely to occur (Holmes 1997). A lack of fire may render habitat unsuitable for nesting through trees and shrubs becoming established and shading the growth of suitable grassy ground cover, grassy tussocks becoming too old and collapsing or weeds invading (Sandpiper Ecological Surveys 2000a). In some northern locations, fire exclusion or suppression may be causing a change in the vegetation and promote plant communities which are not suitable habitat for the Eastern Bristlebird (Stewart 2006). Habitat studies suggest that a fire frequency of 5-15 years will maintain suitable habitat (Lamb et al. 1993; Hartley and Kikkawa 1994). In general, a fire regime of 7 to 10 years frequency is considered to be appropriate for the maintenance of grassy habitat for the northern population (Holmes 1998). However, individual sites require specific assessment. Some higher intensity and more frequent fires may be required in degraded unoccupied habitat to restore the habitat to suitable condition.
There have been many investigations into the effects of fire regimes on the Eastern Bristlebird’s heathland habitat (e.g. Forshaw et al. c1969; Gilmour 1983; Pyke et al. 1995; Baker 1997, 2000; Bain et al. 2008). Generally, densities of Eastern Bristlebirds increase with time since fire and are highest in vegetation of the oldest fire age. Populations have been found to recover more quickly from large-scale fire when unburnt refugia are available, as was the case after the Booderee NP wildfire in 2003 (Bain et al. 2008; Lindenmayer et al. 2009). Studies following large-scale and/or frequent fires in Barren Grounds and Nadgee NRs have indicated that population recovery may take over 10 years when there is a lack of refugia (Gilmour 1983; Baker 1997, 2003; Woinarski and Recher 1997).
Predation of the Eastern Bristlebird by native and feral predators is known to occur (e.g. Clarke and Bramwell 1998; Hartley and Kikkawa 1994; J. Baker unpubl. data; J. Young unpubl. data) but the extent of this at a population level is unknown. Potential native predators include birds of prey, snakes, goannas, quolls, currawongs and honeyeaters, while potential feral predators include cats, foxes, rats, dogs and pigs. The brood parasitism of cuckoos may also impact on Eastern Bristlebirds, Fan-tailed Cuckoos have been known to parasitise nests in south-eastern Queensland (J. Young pers. comm. 2006).
The Eastern Bristlebird’s long incubation period and close proximity of nests to the ground are likely to make nesting birds, eggs and young particularly susceptible to predation (Hartley and Kikkawa 1994). The bristlebird’s habit of calling and showing themselves may also make birds and their nests susceptible to predation. Charley (2010) suggests that nest predation and/or disturbance may affect a large proportion of nesting attempts in the northern population each year. The impact on recruitment is unknown, but likely to be significant.
Small to medium sized ground-dwelling fauna are particularly susceptible to predation by feral cats (Felis catus) and foxes (Vulpes vulpes). A predation study at Howe Flat suggests that cats and foxes appear to provide the greatest predation threat to that Eastern Bristlebird population, with cats more likely to prey on adults than foxes or dogs (Canis lupus familiaris or Canis lupus dingo), but all three (and especially cats and foxes) are likely to take nestlings and juveniles (Mitchell 2001). Feral cats are a consistent presence at Barren Grounds NR (F. Kristo pers. comm. 2010) and cats are thought to be the main feral predator in the northern population (Hartley and Kikkawa 1994). At Howe Flat foxes are moderately common but cats are not abundant (Mitchell 2001).
While systematic control of dogs and foxes is both feasible and cost effective through use of buried 1080 baits, control of cats is much more difficult and expensive as it currently requires live trapping or shooting. Mitchell (2001) suggested that, at Howe Flat, care should be taken with fox control alone as a reduction in fox numbers could result in an increase in the cat population, thus having a greater impact on the Eastern Bristlebird. This is consistent with the mesopredator release theory, which suggests that where fox numbers are declining, feral cats should increase their activity. Control programs may also impact on dingo populations, thus affecting their function as a high-order predator and possibly leading to an increase in numbers of foxes and cats (Glen et al. 2007; NSW Scientific Committee 2008b; DECC 2009; DECCW 2010).
Claridge et al. (2010), however, monitored the activity of wild dogs, foxes and cats during a 10-year fox-baiting program in south-eastern NSW and found that the relative abundance of all three feral predators is much more complex than previously thought. The authors reported no increase in cat numbers during the long-term intensive fox-baiting program.
“Predation by the European Red Fox (Vulpes vulpes)” and “Predation by feral cats” have been listed as Key Threatening Processes under the EBPC Act, and threat abatement plans have been prepared (DEWHA 2008a, 2008b). Further information is required to quantify the overall impact of cat and fox predation on the Eastern Bristlebird.
Fire and feral predation - interaction between threatening processes
Fire is thought to lead to increased predation (Recher and Christensen 1981; Brooker and Brooker 1994; Loyn 1997) for cover-dependent species such as the Eastern Bristlebird. After fire, reduced ground cover may result in greater numbers of birds in small refuge areas, less protection for individual birds and/or easier access for feral predators. Lindenmayer et al. (2010) concluded that the decline of Eastern Bristlebirds after fire is largely due to the exposure to exotic predators following the loss of dense protective cover during a fire. The interaction between fire and feral predators requires further investigation (Bain et al. 2008).
Habitat disturbance by exotic herbivores
Feral pigs (Sus scrofa)
“Predation, habitat degradation, competition and disease transmission by feral pigs” has been listed as a key threatening process under the EBPC Act, and a threat abatement plan has been prepared (DEH 2005). Feral pigs can impact on the Eastern Bristlebird through destruction or disturbance of habitat, spreading weeds and diseases (includingPhytophthora cinnamomi); and increasing access for feral predators such as the European Red Fox. Feral pigs can also affect the species directly by consuming chicks and eggs, along with various components of its diet and habitat.
Overgrazing by domestic livestock is a potential threat to northern populations, particularly during the breeding season. Grazing by exotic herbivores degrades habitat, destroys nests and probably limits dispersal of the most severely threatened populations (Holmes 1989). In addition, the promotion and planting of exotic legumes for fodder is degrading habitat and may lead to the replacement of native grasses (D. Charley pers. comm. 2010).
Limited seasonal grazing on some of the habitat on private land may be beneficial in controlling introduced legumes and shrub development, if undertaken outside the breeding season (Charley 2010).
Habitat degradation due to dieback or invasive weeds
The dieback disease caused by the root-rot fungus Phytophthora cinnamomi is listed as a Key Threatening Process under the EBPC Act, and a threat abatement plan has been prepared to provide a national strategy to manage its impact on biodiversity (DEH 2001). Although dieback has the potential to impact on the habitat of the Eastern Bristlebird, to date there is no evidence of widespread loss of habitat. The pathogen may be spread by the tyres of vehicles or on walking boots, especially during the period of the infective southern spring. The spread of dieback resulting from human activity can be reduced by limiting human access to certain areas (quarantine). However it is also spread by natural vectors such as native or feral animals which can be more difficult to control (DEH 2001).
Bell Miner associated forest dieback (BMAD) is affecting extensive areas of forest in north-eastern NSW and south-eastern Qld. This has been identified as a significant threat to the long-term survival of the open grassy forests of the region and is a potential threat to Eastern Bristlebird habitat (Charley 2010). The BMAD working group has identified strategies to reduce the impact of BMAD (BMAD working group 2010).
Invasion of weeds into the habitats of threatened species is widely accepted as a limiting factor in the effective management of those species. Control of invasive weed species is important for maintenance of habitats in all Eastern Bristlebird populations. It is important to note however, that Eastern Bristlebirds in Booderee NP can utilise Bitou Bush (Chrysanthemoides monilifera subsp. rotundata) as it has the low dense vegetation structure required by the species.
Species such as Lantana (Lantana camara), Crofton Weed (Ageratina adenophora) and Mist Flower (A. riparia) are all significant threats to the habitats of the northern population. Bitou Bush occurs in Booderee NP, and may be a problem for other locations throughout the Eastern Bristlebird’s range. Blackberry (Rubus fruticosus aggregate) poses a weed problem at Howe Flat in Victoria.
Bitou Bush, Lantana and Blackberry are all listed in the top 20 Weeds of National Significance (WONS), identified by the Australian and state governments because of their invasiveness, impacts on primary production and the environment, potential for spread and socioeconomic impacts (DEH 2003a, 2003b, 2003c).