Grey Teal Research Articles

An outbreak of botulism in wild waterbirds in southern Australia.

An outbreak of Type C botulism in waterbirds was investigated at Lake Lalbert in northwestern Victoria, Australia. Total losses were estimated at 1,500 birds, with 80% of affected birds being grey teal (Anas gibberifrons). The outbreak was associated with a falling water level, and extensive decomposition of plant material.

An Experimental Investigation of Filter-Feeding on Zooplankton by Some Specialized Waterfowl.

A study was made of the filtering ability and anatomy of the mouthparts of 4 species of waterfowl: pink-eared duck, Australasian shoveler, freckled duck and grey teal. The first 3 are highly specialized for filter-feeding on zooplankton whereas the last is a more generalized anatid. The pink-eared duck and Australasian shoveler have the filtering lamellae on the bills variously elaborated, whereas the grey teal is similar to published descriptions of the mallard. The freckled duck has bill features more characteristic of flamingoes. On the basis of anatomy it was predicted that pink-eared ducks should be able to filter the smallest particles, followed by shovelers, freckled ducks and grey teal. In feeding experiments the proportions of plankton of various sizes removed by the species was compared. For the 3 specialists the distributions of proportion removed compared with plankton size was, in general, best fitted by a threshold model as follows: y = 1.0[x > P]; y = aebx[60 mu m < x < P], where P is a threshold size above which all plankton can be filtered, y is the proportion filtered out and x is the size class of the plankton (in mu m). Grey teal were inefficient feeders on plankton and gave results only poorly fitted by a simple linear model. The 3 specialists had significantly different threshold sizes, and the results indicated that pink-eared ducks were the most able filterers, followed by freckled ducks, then Australasian shovelers. The failure of a simple mechanistic analysis of anatomy to predict filtering ability is discussed. On the basis of the abundance of these specialized filter-feeders possibly being related to plankton abundance, counts of pink-eared ducks and Australasian shovelers were regressed against plankton counts for a semi-permanent lake in western New South Wales. No simple relationship was found, and the significance of planktivory in these species is discussed.

Hunter Activity and Waterfowls Havests in New South Wales, 1977-82

The results of six annual surveys of waterfowl hunters in New South Wales by mail card are reported. The aims of the survey were to ascertain reported distribution of hunting effort, size and composition of hunters' bags, and state of hunter origin. Hunting effort and waterfowl harvests were highest in southern inland New South Wales. Seasonal bag sizes varied between 15.8 and 27.2 ducks per hunter. Pacific black duck, grey teal and maned duck made up 88.6% of hunters' bags. About half the hunters in New South Wales originated from Victoria. Bag size and species composition, effect of reducing bag size on total harvest, regional bias in hunting effort and harvest, and annual variation in licence sales are discussed.

Bias in Food Habits of Australian Waterfowl.

Most food studies of Australian waterfowl have relied on gizzard analyses. This introduces bias because of differential digestion rates. Oesophageal and gizzard contents collected from feeding grey teal (Anas gibberifrons) and pink-eared duck (Malacorhynchus membranaceus) at 2 sites in south-western New South Wales were determined. Pink-eared duck ate 99.6% animal food (mainly chironomid larvae and ostracods); grey teal ate 74.2% animal food (mainly corixids and dipteran larvae) at one site but 63.9% plant food (mainly grass seeds) at the other. Both species contained higher proportions of animal material in their oesophagi than in their gizzards. Rank correlation analyses showed no significant relationships between oesophageal and gizzard contents in the 2 species in this study, nor in other Australian and overseas waterfowl reported in the literature. It is suggested that gizzard analysis has led to overestimation of the importance of seeds in the diet of Australian waterfowl and underestimation of the importance of invertebrates. It is recommended that future food habits studies of waterfowl use oesophageal contents from feeding birds, and results from previous gizzard studies be treated with caution.

Waterbird Populations in the Brisbane Region, 1972-83, and Correlates with Rainfall and Water Heights

Mean numbers and annual variation of 52 species of waterbirds (families Podicipedidae; Pelicanidae; Anhiigidae; Phalacrocoracidae; Ardeidae; Ciconiidae; Plataleidae; Anatidae; Rallidae; Jacanidae) from the Queensland Ornithological Society's records of the Brisbane region during 1972-83 are presented. Changes in the numbers of many species showed significant negative correlations with changes in the Moreton winter rainfall (3 months before the count). Changes in numbers of hardheads, grey teal and Eurasian coot also had significant negative correlations with changes of inland rainfall, and many other species showed similar trends. Changes in numbers of darter and pied cormorant were positively correlated with changes in Moreton and Warrego rainfall respectively. Most species had non-significant correlations with Moreton dam levels, but for chestnut teal, white-faced heron and dusky moorhen these approached statistical significance (P<0.1). Numbers of whitefaced heron, black swan, comb-crested jacana and darter decreased, and those of Australian pelican and plumed and wandering whistling-ducks increased during the survey period. The coastal and inland distribution of some species is also presented.

Modelling a Climatically Pulsating Population: Grey Teal in South-Western Australia

The south-western population of grey teal (Anas gibberifrons gracilis) undertakes a regular seasonal migration between its winter/spring breeding area in the sub-interior of the continent, and its summering refuges on the coastal plain. An attempt is made at numerically modelling fluctuations of population in response to rainfall. In the rare years with heavy rainfall in the Arid Zone breeding pairs fly to the normally dry lakes, then temporarily flooded, and a great increase in numbers may result. Remote sensing may assist in esti- mating the extent of flood-water habitats. It is suggested that during a more favourable paleoclimatic phase the present Arid Zone may have been the normal habitat for the species; the much wetter present-day habitats of related sub- species may be relevant indicators. Finally, a parallel is drawn with the seasonal migration of the climatically homologous south-western population of the ruddy shelduck Tadorna (Casarca) ferruginea between North Africa and southern Spain.

Mortality of MAned Duck and Grey Teal during the 1982 Open Season at Barrenbox Swamp, N.S.W

Mortality of maned duck and grey teal due to hunting at Barrenbox Swamp in New South Wales in 1982 was estimated from band returns. Birds were marked a short while before the open season commenced. The mortality rates were 33.0% in maned duck and 10.9% in grey teal on opening morning, and 41.0% and 14.3% for the season. The validity of the estimates is discussed. Barrenbox Swamp is a popular hunting site and a permanent wetland. Hunting mortality at the level recorded for maned duck in this study could be detrimental to waterfowl during droughts, when populations concentrate on such permanent waters.

Waterbird Dynamics in the RIchmond VAlley, New SOuth Wales, 1974-77

'Monthly waterbird counts from February 1974 to June 1977 at six wetlands in the Richmond River valley in northern coastal New South Wales were analysed to investigate relationships between numbers of each species, and season and water variables. Black swan, Pacific black duck, purple swamphen, dusky moorhen, cattle egret, comb-crested jacana and sharp-tailed sandpiper were strongly influenced by season. Grey teal, straw-necked ibis, little black cormorant, Pacific heron and black-winged stilt numbers were related to Murray River discharge, an index of inland wetland availability in New South Wales, northern Victoria and parts of southern Queensland. Numbers of most waterbirds were highest on the coast from late summer to the end of winter. Their seasonal abundance patterns conform with the results of some previous studies but differ somewhat from others.

Response by Waterfowl to Hunting Pressure: A Preliminary Study

The movements of ducks to refuges in response to hunting pressure were investigated during the opening of the 1981 duck season. Grey teal, Pacific black duck, hardhead and Australasian shoveler actively sought refuge whilst pink-eared duck did not. Some implications for management are discussed.

Rates of Recovery of Bands, Harvest Patterns and Estimates for Black Duck, Chestnut Teal, Grey Teal and Mountain Duck Shot during Victorian Open Seasons, 1953-1977

The temporal distribution of recoveries of bands from black duck Anas superciliosa, chestnut teal A. castanea, grey teal A. gibberifrons and mountain duck Tadorna tadornoides shot in Victoria during open seasons on waterfowl between 1953 and 1977 is examined. Recoveries were higher on the opening day and during the opening week of each season; recoveries on Saturdays exceeded those on other 'days', and Sunday recovery totals were minimal. No increase or long-term trend in weekday recoveries, and hence shooting, was evident during the study period. Speculative harvest estimates are provided for 1972-77, but such figures must be refined and related to data concerning specific population sizes and distribution before implications for management can be formulated.

Food of the Black Duck and Grey Teal in Coastal Northern New South Wales.

The study area of 500 km2 was humid and subtropical, on flood plain near Coraki, New South Wales. Gut contents were examined and the percentage by volume of different food items is tabulated for black duck (Anas superciliosa) and grey teal (A. gibberifrons). Black duck fed on flooded meadow-grass flats in autumn, moving when the flats dried to seasonal swamps, and when those also dried, to lagoons. Diet varied with place. Seeds of grasses, swamp plants and lagoon plants were eaten, with water snails and water beetle adults and larvae, water spiders and ostracods, and terrestrial invertebrates being eaten when the dry flats became flooded. They ate also waste maize grain from harvested fields before ploughing. Grey teal fed in the seasonal swamps in winter and then left the area almost completely; they ate almost the same items as black duck but fed by the muddy edges of seasonal swamps more than the black duck did. It was known that black duck strip seed from the growing plant and grey teal pick up the fallen seed.

Status, mortality, and movements of grey teal(Anas gibberifrons)in New Zealand

Grey teal (Anas gibberifrons gracilis Buller, 1869) are widely distributed in New Zealand, the greatest concentrations occurring in the South Auckland, Waikato, Hawke's Bay, and Otago districts. Their preferred habitat is shallow freshwater lakes, lagoons, and swamps with extensive marginal cover. The New Zealand population is estimated to be less than 20 000. Grey teal disperse widely in all directions, in some instances for long distances. The composition of flocks changes continually, and pair‐bonds are apparently retained from season to season. There is an almost complete turnover of the population every 4 years. The survival of juveniles in the post‐fledging period is higher for heavier than for light‐weight young. Mortality from hunting is probably additional to the mortality from other causes.

Waterfowl in an inland swamp in New South Wales. 2. Food

The food of nine species of waterfowl has been studied in a drought refuge during a period of moderately severe drought. The species involved were the black swan, freckled duck, black duck, grey teal, shoveler, pink-eared duck, hardhead, musk duck, and blue-billed duck. In all, 3697 gizzards were examined. Although the black swan had certain food plants in common with most other species, particularly during periods of drought, and although the black duck and grey teal had nearly identical food requirements, serious competition between these species was considered unlikely for various reasons. Otherwise, the species were well separated in their feeding places, depths of water utilized, and food collected. The value of cumbungi swamps as drought refuges is discussed and the adaptations of the waterfowl in utilizing these swamps are examined.

Movements and mortality rates of the Black Duck and Grey teal in South-eastern Australia

The movement pattern, mortality, and survival of the black duck are analysed and compared with those of the grey teal. The black duck is more sedentary than the grey teal, although at times extensive movements are undertaken. A regular north-south movement exists in addition to more irregular random dispersal. The mortality rates are shown to be greater and the expectation of further life less for the grey teal than the black duck, the more sedentary species.

Movements of the grey teal, Anas gibberifrons Muller (Anatidae)

The distribution of the habitat of grey teal in eastern Australia is summarized. It is shown that the most important breeding grounds are in the Murray–Darling Drainage Basin; the most important refuge areas are in south-eastern coastal districts. Teal movements are explosive random dispersal and individual birds show very little tendency to return to their point of origin. Despite the random nature of the dispersal regular movements occur to the coast, particularly the southern coast. The numbers of teal in eastern Australia fluctuate greatly. In times of drought irruptions occur and massive mortality follows. It is concluded that the ultimate factor determining the movements and numbers of teal in Australia is rainfall.

The ecology of wild ducks in inland New South Wales. II. Movements

Observational and banding data show that during 1957, a year of drought, a great movement of wild ducks from inland Australia to the coast took place. With continuing drought many of the coastal concentrations again dispersed, the birds flying widely over the interior of the continent, apparently in a search for a suitable habitat. It is shown that the grey teal, Anas gibberifrons Miiller, was very much more mobile than the black duck, Anus superciliosa Gmelin, and that the wood-duck, Chenonetta jubata (Latham), Tvas rather local in its habits. The ecological significance of the different mobility of those species is discussed.

The ecology of wild ducks in inland New South Wales. III. Food habits

The food habits of the wood-duck (Chenonetta jubata (Latham)), black duck (Anas superciliosa Gmelin), grey teal (A. gibberifrons Muller), blue-winged shoveler (A. rhynchotis Latham), pink-eared duck (-Malacorhynchus membranaceus (Latham)), and white-eyed duck (Aythya australis (Eyton)), are discussed and compared. These six species are the most common, and economically the most important, wild ducks occurring in inland Australia. It is shown that the numbers of different food items are relatively small, and that all the species studied eat the same materials but in varying proportions.

The ecology of wild ducks in inland New South Wales. IV. Breeding

The breeding of the black duck, Anas superciliosa Gmelin, the grey teal, A. gibberifrons Muller, and the pink-eared duck, lialacorhynchus membranaceus (Latham) has been studied. The breeding of the grey teal is timed to coincide with increasing water level, and that of the pink-eared duck with declining water level following flooding. Both species may breed at any time of the year when the appropriate water conditions occur. The emergence of ducklings in each species coincides with a great increase in the animal food available to them. That increase in animal food is initiated by the original alteration in water level. The black duck has a more regular breeding season than the other species, and some birds breed even though the season is adverse. Out-of-season breeding may occur, however, whenever exceptionally favourable conditions are present. It is concluded that, although environmental factors are of prime importance in regulating sexual activity in wild ducks, the influence of fixed annual factors (including long-term photoperiodism) on some species cannot be entirely ignored.

Relationship between some coastal fauna and arthropod-borne fevers of North Queensland.

FOLLOWING on an outbreak of dengue fever in Townsville, North Queensland, in the early months of 1954, O'Connor et al. 1 found that the sera of some members of species of flying foxes (genus Pteropus) gave positive protection tests against the dengue type 1 (Hawaiian) strain. At the same time sera were collected from locally migratory birds, the black duck (Anas superciliosa) and grey teal (Querquedula gibberifrons), which mainly frequent the inland swamps, and also from wading birds (Charadriiformes) along the sea shore. These latter are found on the mudflats and sandpits, which are often in close proximity to the mangrove swamps where the flying foxes camp during daylight hours.

Wild ducks and the rice industry in New South Wales

The ecology and economics of wild ducks in the irrigated rice-growing areas of New South Wales have been investigated. Grey teal and black duck periodically cause some damage to crops; but only a small part of the population is involved, and the attacks are usually confined to those areas in the crops where growth is unsatisfactory for other reasons. The wood duck is capable of causing more serious damage to rice, and on some occasions does appreciable damage to isolated or neglected crops. The amount of damage caused by ducks is correlated with climatic conditions; and it is concluded that wild ducks are, on the whole, a very minor pest to the rice-growing industry. The value of shooting and the importance of cultivation practices in relation to the duck problem are discussed.