Justification of Red List Category
This species is listed as Endangered because it has a very small and rapidly declining population owing to the loss and degradation of its wetland habitats. Urgent action is a priority to halt declines in Australia.
In New Zealand, the estimated population was between 580-725 individuals in 1980. The population on New Caledonia is not thought to exceed 50 individuals. Following apparently rapid declines, the Australian population is now thought to number fewer than 1,000 mature individuals (R. Loyn in litt. 2008). The total population is best placed in the band 1,000-2,499 mature individuals, equating to 1,500-3,749 individuals in total, rounded here to 1,500-4,000 individuals.
Population trends are unknown for the small New Caledonian population, whilst in New Zealand (c.40% of the global population) the species is suspected to be stable. In Australia, however, reporting rates in atlas surveys have declined by 77% since the first atlas in 1977-1981 and 58% since the second atlas in 1998-2003. This equates to an overall population decline of c.38% over the past three generations, or 26% over the past two generations.
Botaurus poiciloptilus occurs in the wetlands of southern Australia, New Zealand and New Caledonia (to France). In Australia, the population is now estimated to number not more than 1,000 mature individuals (R. Loyn in litt. 2008) and is probably between 247 and 796 (Birds Australia in litt. 2011). Birds Australia (now BirdLife Australia) estimated the number of adult birds in 2009-2010 to be 3-16 in Queensland, 82-162 in New South Wales, 86-248 in Victoria, 12-100 in Tasmania, 26–116 in South Australia and 38-154 in West Australia (Birds Australia in litt. 2011). Consecutive atlas censuses in Australia have shown a marked decrease in reporting rate; the species was recorded in 260 10-minute grid squares in 1977-1981, 142 grid squares in 1998-2003, and just 61 in 2003-2008 (J. O'Connor in litt. 2008). The declining reporting rate was particularly pronounced in the Riverina (63%), Tasmania (>90%), and south-west Australia (>90%). This decline in reporting rate is thought to represent a genuine population decline over the period. In Australia, most birds are in the Murray-Darling basin and adjacent coastal areas. In Western Australia, the population was estimated to contain up to 100 pairs in 1980 (Marchant and Higgins 1990), but it is now much reduced, with the largest concentration in the Albany and Lake Muir wetlands. There have been no confirmed records from the Swan Coastal Plain since 1992 and surveys conducted in 2007 and 2008 found that half the wetlands that supported the species in 1980 now retained no suitable habitat (Pickering and Gole 2008). There are now only occasional records from Queensland (Garnett and Crowley 2000) and there appears to have been no great influx to remnant wetlands after the recent drought, as might have been expected if they were more common inland. In South Australia, breeding is confined to the south-east, however, loss of suitable habitat at Bool Lagoon, arguably the key site in Australia for this species, and other wetlands in the area owing to changes in regional drainage, has probably had a large impact in the last 10-20 years (R. Jaenesch in litt. 2003). It is now known from just one site, Hirds Swamp, in Victoria (G. Dutson in litt. 2008). In Tasmania, the species is now recorded from only a handful of sites and several of the major lakes that it once occupied have been dry for some years. In New Zealand, the estimated population was between 580 and 725 individuals in 1980 (Heather and Robertson 1997); numbers may be greater, given the lack of targeted survey work, and the large size of suitable swamps (G. H. Sherley in litt. 1999). In New Caledonia and Uvea, there have been just two recent records of single calling males, and the population is not thought to exceed 50 individuals (N Barré in litt. 1999, Ekstrom et al. 2000).
It has fairly specific habitat preferences, preferring shallow, vegetated freshwater or brackish swamps where there is a mixture of short and tall emergent sedges and rushes (Garnett 1992). It has been recorded in rice paddies in the Murray Darling basin, but it is not thought to use such habitats for breeding (G. Dutson in litt. 2008). It usually lays four eggs. It feeds, mostly at night, on fish, eels, frogs, freshwater crayfish and aquatic insects (Heather and Robertson 1997). The population seems to increase rapidly in good years and decline rapidly in poor ones (S. Garnett in litt. 2003). The species appears to disperse widely, including to coastal wetlands during periods of drought and to ephemeral wetlands during and after periods of rainfall (Garnett et al. 2011).
In Australia and New Zealand, the main threats are wetland drainage for agriculture, as well as changes brought about by high levels of grazing and salinisation of swamps (Garnett 1992, B. D. Bell in litt. 1994, Garnett and Crowley 2000). In Australia, the species appears able to adapt to the availability of ephemeral wetlands, but is likely to be particularly sensitive to the destruction of drought refugia. Loss of these habitats may explain its decline in Western and South Australia (Garnett and Crowley 2000). The Murray-Darling basin, a former stronghold of the species, has suffered consecutive droughts in recent years and over-extraction of water is an on-going problem (H. Ford in litt. 2008, R. Loyn in litt. 2008). In Australia, introduced red foxes Vulpes vulpes are thought to take eggs and juveniles (Smith et al. 1995). Overgrazing and inappropriate fire regimes can also reduce habitat suitability (Marchant and Higgins 1990). Nests have been reported to be abandoned following visits by people, implying that the species is sensitive to disturbance (O’Donnell 2011). Shooting and flying into powerlines are additional contributory causes (B. D. Bell in litt. 1994), but hunting pressure is very low (N. Barré in litt. 2003).
Conservation Actions Underway
In Australia, Bool Lagoon and Lake Muir are managed specifically for the species (Garnett and Crowley 2000). Recent initiatives by the Threatened Bird Network in Australia to survey Painted Snipe Rostratula benghalensis australis will contribute to the information on the distribution of this species (C. Tzaros and M. A. Weston in litt. 2003, G. Dutson in litt. 2008). BirdLife Australia (formerly Birds Australia) started a Bittern Project in 2007. In 2011, the species was added to the list of Australia’s threatened species recognised by the Environment Protection and Biodiversity Conservation Act as Endangered.
71 cm. Large, brown bittern. Brown-and-buff mottling. Thick neck. Partly nocturnal. Voice Deep booming calls during breeding.
Text account compilers
Benstead, P., Bird, J., Butchart, S., Dutson, G., Garnett, S., Harding, M., Mahood, S., Pilgrim, J., Taylor, J., Allinson, T & Symes, A.
Barré, N., Bell, B., Blyth, J., Burbidge, A., Christidis, L., Ford, H., Garnett, S., Herman, K., Holmes, T., Jaensch, R., Loyn, R., Miskelly, C., O'Connor, J., O'Donnell, C., Sherley, G., Tzaros, C., Wakefield, B. & Watson, D.
BirdLife International (2019) Species factsheet: Botaurus poiciloptilus. Downloaded from http://www.birdlife.org on 12/12/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 12/12/2019.