Blue-billed Duck (male). Image courtesy of Richard Hall photography
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The Blue-billed Duck Oxyura australis is a stiff-tailed diving duck. Its genus name Oxyura is derived from the Greek oxys -sharp and oura - tail. The adult male has a distinctive sky-blue bill, glossy black head and chestnut body plumage, which is most evident during the breeding season but may remain throughout the year.
Non-breeding plumage in males can vary and the bill can appear grey in partial eclipse or dark green in full eclipse plumage. Females are brownish-grey with pale barring and do not have plumage change. It can be difficult to distinguishing between males in full eclipse plumage, females and juveniles.
Non breeding male, female and immature Blue-billed Ducks can appear similar to the female Musk Duck, which is also a stiff-tailed diving duck. Distinguishing features include more rounded head of the Blue-billed Duck and a concave bill rather than the triangular bill of the Musk Duck. The Blue-billed Duck is noticeably smaller than the Musk Duck, males being about 60% shorter and females 30% shorter (Marchant & Higgins 1990, Simpson & Day 1999).
Victorian distribution
The Blue-billed Duck occurs in Australia's temperate regions, in both southwest Western Australia and the eastern Australia. The highest concentrations in eastern Australia are in southern Victoria. The Australian population is estimated at 12,000 breeding birds (Environment Australia 2000), although the majority are found on artificial wetlands, for example the main site for this species in Victoria is the Melbourne Western Treatment Works at Werribee.
Historic records of Blue-billed Duck in Victoria. Source: Department of Environment, Land, Water & Planning, September 2015.
Counts of waterbirds on Victoria's wetlands over five years (1988-1991) indicated the Blue-billed Duck population could be at least 1600 in Victoria (Peter 1991). A more recent analysis of 73 counts between the years 2000 - 2012 at the Western Treatment Plant wetlands at Werribee found an average of 4078 Blue-billed Ducks. In 2013 in excess of 10,000 Blue-billed ducks were recorded in this area (Loyn et al. 2014).
It has been noted that Blue-billed Ducks tend to congregate at the Western Treatment Plant wetlands in drought years when habitat across their range becomes unsuitable. They tend to disperse in years when other wetlands hold more suitable water levels.
The Victorian Summer Waterbird Counts demonstrate how the population count can vary. The 2011 Victorian Summer Waterbird Count only recorded 15 Blue-billed Ducks (Purdey and Loyn 2011). The 2012 Victorian Summer Waterbird Count recorded 845 Blue-billed Ducks; Port Phillip (793 mostly at the Western Treatment Plant), North East (8), North West (16), Gippsland (15), South West (13). The 24 year long-term average of Blue-billed Ducks in the Victorian Summer Waterbird Counts is 3779 (Purdey and Loyn 2013).
The 2014 and 2015 summer waterfowl counts found the Port Phillip Region (i.e. Western Treatment Plant) held most of the Blue-billed Ducks counted across Victoria (98.3% in 2014; 92.2% in 2015) (Purdey & Menkhorst 2015).
If the populations on artificial wetlands/treatment ponds were excluded a more accurate reflection of Blue-billed Duck status in natural habitats would emerge, where flocks in excess of 90 birds are uncommon and many wetlands support less than 10 birds.
In Victoria there are only 25 wetlands which have records of 100 or more Blue-billed Ducks. There are only 17 wetlands in Victoria where Blue-billed Ducks have been recorded breeding.
The Mallee CMA commissioned the Arthur Rylah Institute (ARI) to examine data on Blue-billed Ducks in the region, collected during annual Summer Waterfowl Counts between 1984 to 2008. Blue-billed Ducks were recorded at 49 wetlands within the study area. The study also found that numbers of Blue-billed ducks have declined in the period between 1984 and 2008 (Purdey & Loyn 2008).
The most important wetlands for Blue-billed Ducks with (mean average) in descending order were Lake Wandella (45), Irymple Tank (36.7), Wargan Channel east ponds (23.6), Wallpolla Creek (20), Round Lake (16.4) , Wargan Channel (10.6), Tutchewop (98), Koorlong Lake (96), Wargan Channel north-east (8.8), Benetook Swamp (7.5), Lake Elizabeth (6.4) and Cullens Lake (6.2).
The maximum count was 374 at Lake Wandella on 14 March 1992. All high counts were recorded in the 1980s and 1990s except for a count of 100 at Round Lake on 23 February 2000.
Round Lake and Lake Elizabeth may now be the only wetlands in the region to support regular large flocks of Blue-billed Duck (Purdey & Loyn 2008). Round Lake was closed to hunting in 2015 due to high numbers of Blue-billed Ducks (Purdey & Menkhorst 2015).
Note: this is not intended to be a complete list of every wetland that has a record of Blue-billed Ducks in Victoria but rather wetlands which have a high probability of occurrence provided conditions are suitable.
Habitat & ecology
The Blue-billed Duck inhabits fresh to saline, deep permanent open wetlands and deep, densely vegetated lakes. During the breeding season (November - March) there is a tendency to disperse to deep freshwater wetlands that have abundant aquatic and emergent vegetation although many birds remain on large wetlands (Hewish 1988).
Blue-billed duck family. Image courtesy Peter Menkhorst.
Ducklings stay under the care of the female duck for the first 4-5 weeks.
In winter, Blue-billed Ducks may congregate in large flocks on large clear lakes and more saline wetlands, preferring open water usually away from the shoreline. The level of movement is likely to be influenced by seasonal conditions such as rainfall, lake levels and water salinity.
A study of Blue-billed Ducks in North West Victoria between 1984 and 2008 found that numbers were highest in years when Murray River tributary rivers at Quambatook, Wakool Junction and Loddon River, Kerang had high flow rates i.e. wet years (Purdey & Loyn 2008).
Suitable breeding sites may hold winter flocks, provided they contain dense marginal vegetation and large expanses of open water, which could explain why some males remain sedentary and retain full breeding plumage into winter. Nests are mostly solitary and constructed in spring on low trampled swamp vegetation such as rushes and sedges.
Female Blue-billed Duck - note the stiff tail feathers.
The Blue-billed Duck feeds on variety of aquatic insect larvae, molluscs and aquatic plant material including leaves and seeds. They have a diving habit and stay underwater for up to 30 seconds per dive (Emison et al. 1987, Marchant & Higgins 1990).
The main threat is loss of suitable wetland habitat;
The high concentration of Blue-billed Ducks on areas such as the Melbourne Western Treatment Works at Werribee tends to disguise what has happened to populations on natural wetlands which have been impacted upon by reduced water levels and higher salinity levels in recent years.
The long term impacts from the now banned use of lead shot is unclear, but may pose an on-going problem in some waters which were subject to heavy hunting in the past. Lead poisoning is known to occur at a much higher incidence for diving ducks (Pain 1992).
The Blue-billed Duck is a protected species which must not be hunted (Game Management Authority). Impacts from hunting may have been a factor in the past, for example in 1987 it was recorded that 61% of Blue-billed Ducks counted on Victorian wetlands were on waters open to hunting and 2.1% of these ducks were illegally harvested, this equated to an estimated 1.3% of the entire pre-season count (Loyn 1987). As the number of viable wetlands has been reduced over the last 15 years or so due to low water levels the impact of hunting could be exacerbated as it is concentrated on fewer wetlands. This situation has been managed to some extent by altered duck hunting arrangements such as reduced hunting season and water closures. In addition, the level of illegal harvest has been minimised through improved hunter identification and licensing procedures.
Blue-billed Duck (male). Image courtesy of Richard Hall photography
(Purdey & Loyn 2008).
Blue-billed Duck (male). Image courtesy of Peter Menkhorst.