Data Zone
Justification of Red List category
Despite this species having a large range, reporting rates and the impacts of recent fires indicate rapid population declines in the last three generations, and this decline is likely to continue with climate change projections. For these reasons the species is assessed as Vulnerable.
Population justification
The estimate used here is the product of three predicted AOO measures (spanning 22,700-40,000 km2) from Cameron et al. (2021), the smallest being the number of 2x2 km squares for which there are records since 1990, the latter being an arbitrary value of nearly double this to account for incomplete survey effort of potentially suitable habitat. The density applied assumes an average density of 3.1 birds/km2, that the 2019–2020 fire season reduced the carrying capacity of 40% of grid cells by half and resulted in 10% mortality (Cameron et al. 2021). Combining these measures and uncertainty creates a likely population estimate of between 17,600 and 35,200 mature individuals, with a most likely figure (the midpoint) of 25,300.
Trend justification
It is estimated that the 2019–2020 fire season reduced the carrying capacity of 40% of grid cells by half and resulted in 10% mortality (Cameron et al. 2021). Apart from fire impacts, trend data are not entirely consistent. Reporting rates from 500-m radius area searches (20,094 individuals; 328,201 surveys), arguably the most reliable of the available survey methods for the species, declined by 69% from 1999–2019. This follows a significant decline of 22% between 1977–1981 and 1998–2001 (Barrett et al. 2002), including a decline of 44% in New South Wales (Barrett et al. 2007).
However, the decline in 2-ha 20-min surveys from 1999–2019 (8,987 individuals; 267,885 surveys) was only 15% (BirdLife Australia 2020). In the Australian Capital Territory, reporting rates were three times higher in 1987–1989 than the fairly stable reporting rate since (Canberra Ornithologists Group 2020). Combining these analyses and incorporating temporal and spatial uncertainties, Cameron et al. (2021) best estimated a global rate of decline of 30-49% over the past three generations (27 years; Bird et al. 2020).
Gang-Gang Cockatoos occur along the Great Dividing Range, Australia, from the Hunter Region of the central north coast of New South Wales in a broad arc around south-eastern Australia to the Otway Ranges and inland as far as Wagga Wagga, Albury, Rutherglen, Seymour and Ballarat with largely isolated subpopulations in the Otway Ranges, Grampians and south-western Victoria to the South Australian border. Until the 1960s, they also occurred on King Island in Bass Strait.
Gang-gang Cockatoos occur in a wide range of forests from the coasts through foothill forests and associated gullies to montane forests and sub-alpine woodlands, favouring mature forests for breeding (Loyn 1985). They also occupy more lightly timbered habitats, including farmland and urban areas, especially during winter when part of the upland population moves to lower elevations (Chambers 1995), also extending into regrowth forests and drier forest types such as box-ironbark (Loyn 1985). Gang-gangs nest in relatively large hollows, with nest height reflecting the structural characteristics of the vegetation (Chambers 1995, Davey et al. 2019). Observations in NSW and the ACT suggest that nests appear to be clustered (NSW Scientific Committee 2008,; M. Mulvaney pers. comm.). Gang-gang Cockatoos typically lay two eggs (Higgins 1999), though nests containing three young have been recorded (Davey et al. 2019). Their principal native foods are the seeds of eucalypts and acacias, along with other native shrubs (e.g. Persoonia spp.) and insects such as gall insects (Higgins 1999). Exotic foods, such as hawthorn Crataegus monogyna, may be an important part of the diet for some populations, as can suburban plantings of out-of-range eucalypts (Davey and Eales 2016).
Gang-gang Cockatoos are among the least studied species in the family in Australia, and there is inadequate understanding of the reasons they have been declining (Cameron 2007). Plausible threats include the loss of habitat through land clearing, particularly along the slopes of the Great Dividing Range, and a reduction in nest hollow availability due to forest management practices (NSW OEH 2020). For urban populations, clearing for housing can lead to the destruction of nest sites. Gang-gang Cockatoos breed mainly in mature forest (Loyn 1985) and decline with increasing removal of old trees (Loyn and Kennedy 2009). Fire poses a threat, destroying nest trees and suppressing seed production in key feed species (Koch 2003). Higher temperatures may also be having an effect (Herold et al. 2018), with heat waves implicated in the premature fledging of nestling Gang-gang Cockatoos (Cameron et al. 2021). Extreme fire weather (Di Virgilio et al. 2019, Dowdy et al. 2019) driven by longer and more severe droughts (Evans et al. 2017) and more frequent heat waves (Herold et al. 2018) are likely to increase in frequency and intensity in coming decades. Given the broad-scale reduction in older-aged montane forests (Lindenmayer et al. 2015), and the time required for trees to form large hollows, it is plausible that hollow availability has declined across the range, probably leading to increased competition for hollows from other hollow-dependent birds, mammals and maybe European honey bees Apis melifera (Davey et al. 2019, M. Cameron unpublished, in Cameron et al. 2021). However, most threats are speculative.
Conservation Action Underway
Many birds spend much of their time in protected areas. It is listed as threatened under some State legislation. The ACT population has been subject to long-term population monitoring. Forest management policies generally involve reductions in logging of mature forest.
Conservation Action Proposed
Obtain basic information on demography, mobility, key breeding locations, habitat requirements and threats. Assess the availability of suitable nest hollows and options to ameliorate limitations, if nest site competition or hollow availability is a limiting factor. Assess the impacts of wildfire and prescribed burning, especially on food resources. Assess the availability of food and investigate the impact of global warming on habitat suitability and extent. Determine susceptibility to heat stress. Continue to reduce logging of mature forests, and encourage policies for retaining old trees such as identification and protection of nests sites during forestry operations. Ensure fire management considers impacts on key breeding locations, foraging and nesting habitat. Develop management plans for local populations to ensure resources are available to support viable populations in the long-term. Retain any significant occurrences of exotic or out-of-range native food resources in urban environments or ensure their strategic replacement with alternate food resources.
Text account compilers
Vine, J., Berryman, A.
Contributors
Butchart, S. & Garnett, S.
Recommended citation
BirdLife International (2024) Species factsheet: Gang-gang Cockatoo Callocephalon fimbriatum. Downloaded from
https://datazone.birdlife.org/species/factsheet/gang-gang-cockatoo-callocephalon-fimbriatum on 18/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 18/12/2024.