Black Ducks Research Articles

Dispersal and mortality of juvenile American Black Ducks, Anas rubripes, on wetlands under different management strategies

Dispersal and mortality of juvenile American Black Ducks, Anas rubripes, on wetlands under different management strategies

Reproductive variables of American black ducks along the St. Lawrence estuary, 1963-1991

Reproductive variables of American black ducks along the St. Lawrence estuary, 1963-1991

Meller's duck: A threatened species receives recognition at last

Wetland areas of Madagascar, increasingly threatened by extensive habitat modification, contain many little known endemic species. One of these species, Meller's duck (Anas melleri), is restricted to the eastern slope of the central highlands but for many years was just considered a recent island isolate of the widespread common mallard (A. platyrhynchos) and, therefore, not worthy of protection. Phylogenetic analysis, based on mitochondrial d-loop DNA sequences, indicates that Meller's duck is distinct from the mallard and from its nearest geographical congener, the yellow-billed duck (A. undulata) and may have evolved from a non-dimorphic ancestor, the African black duck (A. sparsa). A decline in numbers of the Near-Threatened Meller's duck highlights the need for adequate protection for Madagascar's wetlands.

Dabbling Duck Behavior and Aircraft Activity in Coastal North Carolina

Requests to increase military aircraft activity in some training facilities in the United States have prompted the need to determine if waterfowl and other wildlife are adversely affected by aircraft disturbance. We quantified behavioral responses of wintering American black ducks (Anas rubripes), American wigeon (A. americana), gadwall (A. strepera), and American green-winged teal (A. crecca carolinensis) exposed to low-level flying military aircrafts at Piney and Cedar islands, North Carolina, in 1991 and 1992. Waterfowl spent ≤1.4% of their time responding to aircraft, which included flying, swimming, and alert behaviors. Mean duration of responses by species ranged from 10 to 40 sec. Costs to each species were deemed low because disruptions represented a low percentage of their time-activity budgets, only a small proportion of birds reacted 'to disturbance (13/672; 2%), and the likelihood of resuming the activity disrupted by an aircraft disturbance event was high (64% ). Recorded levels of aircraft disturbance (i.e., x = 85.1 dBA) were not adversely affecting the time-activity budgets of selected waterfowl species wintering at Piney and Cedar islands.

Perspectives on the diagnosis, epizootiology, and control of the 1973 duck plague epizootic in wild waterfowl at Lake Andes, South Dakota.

An epizootic of duck plague occurred in early 1973 in a population of 163,500 wild waterfowl, primarily mallards (Anas platyrhynchos), wintering on Lake Andes and the nearby Missouri River in southeastern South Dakota (USA). The diagnosis was based on pathologic lesions and confirmed by virus isolation. Control measures included quarantine, attempts to reduce virus contamination of the area, dispersal of waterfowl, and monitoring of wild waterfowl populations for mortality. The epizootic resulted in documented mortality of 18% and estimated mortality of 26% of the waterfowl at risk. Prompt implementation of control measures might have limited mortality to approximately 8%. Losses during the epizootic were equivalent to 0.12% of the annual mortality in the North American 1996 fall population of 80,000,000 wild ducks. The most likely sources of the infection were free-flying wild mallard or American black duck (Anas rubripes) carriers from the upper midwestern or northeastern United States. Duck plague serum neutralization antibodies were demonstrated in 31% of 395 apparently healthy mallards sampled prior to dispersal of the flock at Lake Andes, suggesting that tens of thousands of potential duck plague carriers entered the wild waterfowl populations of all four major flyways. Consequently, the absence of major epizootics of duck plague in wild waterfowl in the subsequent two decades is evidence that substantial numbers of duck plague carriers can occur in wild waterfowl populations without resulting in epizootic mortalities. The failure to isolate duck plague virus from apparently healthy mallards sampled during the epizootic raises questions concerning the validity of conclusions regarding the status of duck plague in wild waterfowl based upon negative results of random surveys conducted in the absence of epizootics.

A Technique for Dorsal Subcutaneous Implantation of Heart Rate Biotelemetry Transmitters in Black Ducks: Application in an Aircraft Noise Response Study

A technique for heart rate biotelemetry transmitter implantation was developed to monitor heart rate fluctuations of Black Ducks (Anas rubripes) in response to simulated aircraft noise in a large outdoor enclosure. A dorsal subcutaneous approach, with subcutaneous tunneling of lead wires, was employed for placement of the 32 g transmitters. A base-apex lead configuration, with leads anchored at the dorsal cervico-thoracic junction and the caudal keel, yielded the maximal ECG wave-form deflection for triggering the transmitter. Heart rates of six Black Ducks (three in each of two separate trials) were monitored for 3 days pre-noise to establish a baseline, and then for 4 days of simulated aircraft noise. The noise stimulus replicated an FB-111 military jet, and was played 48 times per day at a peak volume of 110 dB. Daily mean heart rates, used as indicators of metabolic rates, did not increase in response to noise. Recognizable acute heart rate increases corresponding with a noise event occurred with increased frequency during the first day of noise presentation, but on subsequent days the responses did not differ significantly from baseline. Acute heart rate responses to aircraft noise diminished rapidly, indicating the ability of Black Ducks to habituate to the auditory component of low altitude aircraft overflights.

Could the Blood Parasite Leucocytozoon Deter Mallard Range Expansion?

We investigated whether the blood parasite Leucocytozoon simondi could slow mallard (Anas platyrhynchos) population growth in the east that has been associated with American black duck (A. rubripes; hereafter black duck) population decline. Susceptibility to parasites was compared among F1 ducklings produced from crosses between mallard and black ducks from areas of Leucocytozoon endemicity (Ontario), and between mallards from an area free of Leucocytozoon (Saskatchewan). We produced 6 types of ducklings: Ontario black duck x Ontario black duck (OB x OB), Ontario black duck x Ontario mallard (OB x OM), Ontario black duck x Saskatchewan mallard (OB x SM), OM x OM, OM x SM, and SM x SM. We predicted that because of probable coevolution of black ducks and Leucocytozoon, black duck ducklings would have resistance to the parasite. We also predicted that Ontario genes would confer some resistance to ducklings because these ducklings' parents had survived exposure to Leucocytozoon. In contrast, we predicted that mallard and Saskatchewan genes would not confer resistance, i.e., OB x OB ducklings would have greatest resistance to Leucocytozoon, SM x SM ducklings would have least, and remaining duckling types would have intermediate resistance. Of 169 ducklings exposed in 2 years in 3 geographically separate locales, none died, showed noticeable symptoms, or otherwise behaved abnormally. Nonetheless, weekly blood smears indicated that 91% of ducklings became infected, and many developed intense parasitemias. However, infection intensities were not different among the 6 duckling types. In addition, hematocrits were not lowered by intense infections. These results suggest that the effects of Leucocytozoon on wild waterfowl populations have been overestimated, and that Leucocytozoon will not prevent further range expansion of mallards.

Habitat-related variation in movements and fledging success of American black duck broods in northeastern Nova Scotia

Female American black ducks (Anas rubripes) are known to move their broods from low- to high-nutrient rearing sites. We studied the extent of brood movement and fledging success in a northeastern Nova Scotia watershed. Annually, about half the broods moved either overland or along three rivers from small, widely dispersed oligotrophic–mesotrophic wetlands to a large hypertrophic tidal marsh. Mean brood size at fledging was 3.50 in the tidal marsh but 7.05 at the dispersed freshwater wetlands. Females that remained at dispersed sites fledged more ducklings than females that moved to the marsh. Attrition occurred predominantly in the marsh or in transit. Females fledged fewer young when they raised broods at the marsh than when the same females raised broods at inland sites. Females were as successful at nutrient-poor sites as at nutrient-rich sites. The study suggests that concentrating birds in nutrient-rich sites may be counterproductive in terms of female reproductive fitness and population recruitment.

Scanning and Tail-Flicking in the Australian Dusky Moorhen (Gallinula tenebrosa)

Scanning and Tail-Flicking in the Australian Dusky Moorhen (Gallinula tenebrosa)

Correlates of behavioural dominance in mallards and American black ducks

American black duck, Anas rubripes, populations are thought to be in decline largely because of competitive exclusion by mallards, A. platyrhynchos , and/or introgressive hybridization. Mallard males reportedly are behaviourally dominant to black duck males, which may allow mallards to acquire black duck females as mates and/or exclude black ducks from high-quality breeding sites. The purpose of this study was to examine the influence of body size, body mass, degree of body symmetry and testosterone levels on dominance interactions between these two species, while controlling for effects of previous experience. Thirty dominance trials were performed in the winter and spring with groups of six males (three mallard and three black duck). Surprisingly, mallards were not generally dominant to black ducks. General linear model analyses revealed that morphological and hormonal variables were not consistently correlated with dominance, but place of origin and home pen dominance were. Pre-trial plasma testosterone concentration and change in testosterone concentration were significant effects in the winter trials, but in the opposite direction to that predicted. Size-adjusted body mass was correlated with dominance between Ontario mallards and wild-source black ducks in the spring. Dominance relationships between these two species are more complex than was originally thought.

Exposure of wild waterfowl to Mycoplasma anatis.

We developed an ELISA procedure to assess the presence of M. anatis-specific serum antibody in ducks. Sera from exposed and unexposed Pekin ducks (Anas platyrhynchos) were used to standardize the ELISA and to establish reference ranges to classify ELISA results as exposed or not exposed. We conducted serological surveys of female waterfowl in the central and eastern United States between 1988 and 1992 to assess the frequency of exposure in wild waterfowl. Adult breeding mallards (Anas platyrhynchos), wintering mallards, and black ducks (Anas rubripes) had high prevalences of exposure to M. anatis (25% to > 80%). In comparison, none of the breeding adult canvasbacks (Aythya valisineria) had serum antibody levels indicating exposure. Approximately 50% of the juvenile mallards and black ducks were exposed to M. anatis by 8 months of age, indicating high transmission rates among wild birds.

The diet of insectivorous ducklings and the acidification of small Ontario lakes

We examined the diet of insectivorous ducklings of four species of waterfowl, Common Goldeneye (Bucephala clangula), Ring-necked Duck (Aythya collaris), Hooded Merganser (Lophodytes cucullatus), and American Black Duck (Anas rubripes), collected from small lakes covering a range of acidity in northeastern Ontario. The numbers of Odonata larvae, aquatic Hemiptera, aquatic Coleoptera, and Trichoptera larvae eaten by the ducklings were estimated from combined esophageal and gizzard contents and analysed with respect to differences in lake acidity and fish presence. Ducklings of all species, especially Common Goldeneye and Hooded Merganser, ate significantly more nektonic prey, especially Notonectidae (Hemiptera) and Dytiscidae (Coleoptera), from lakes without fish than from lakes with fish. Ducklings of species other than American Black Duck ate more Anisoptera larvae on acidic lakes. American Black Duck ducklings ate more teneral Odonata on acidic lakes. There was a tendency for more Trichoptera larvae to be eaten on non-acidic lakes than on acidic lakes. All four species adjusted, to some extent, for the absence of acid-sensitive prey in acidified lakes by feeding on prey that are most abundant under acidic, Ashless conditions. Differences in diet among species were related to differences in diving and foraging behaviour, and to hatch date.

Wetland Availability and Use by Breeding Waterfowl in Southern Ontario

Studies have documented breeding waterfowl use of habitat in the Prairie Pothole Region; however, the difficulty in surveying forested areas has inhibited large scale studies of use of habitat in eastern Canada. We examined waterfowl use of 15 wetland habitats in 132,000 km 2 of southern Ontario, Canada. We obtained data from plots that were surveyed by the Canadian Wildlife Service during 1981 and 1987. Open water lakes accounted for 47% of available habitat in the study area; however, they were avoided (P < 0.001) by blue-winged teal (Anas discors), mallards (A. platyrhynchos), and wood ducks (Aix sponsa). Beaver (Castor canadensis) ponds accounted for 25% of the wetland area and were preferred (P < 0.001) by wood ducks and were used by mallards, black ducks (A. rubripes blue-winged teal, and ring-necked ducks (Aythya collaris). Other habitats composed 0-6% of available wetlands and accounted for 0-10% of waterfowl use on study plots in southern Ontario. The percentage of wetlands occupied by breeding waterfowl varied from 11% for bogs and seasonal basins to 50% for deciduous swamps. The more common breeding species in southern Ontario (mallard, wood duck, blue-winged teal) exploited many habitats. Management efforts should focus on emergent or wooded habitats, especially beaver ponds, that provide habitat for many breeding waterfowl.

EFFECT OF EXOGENOUS ADRENOCORTICOTROPIC HORMONE ADMINISTRATION ON PLASMA CORTICOSTERONE CONCENTRATIONS IN AMERICAN BLACK DUCKS (ANAS RUBRIPES)

A protocol for the adrenocorticotropic (ACTH) stimulation test in American black ducks (Anas rubripes) was established with synthetic ACTH, cosyntropin (Cortrosyn); ACTH stimulation testing was conducted on 31 adult ducks (14 males, 17 females) in September 1993. Plasma corticosterone concentrations were measured on heparinized blood samples collected 30 min, and 1, 2, and 4 hr post-injection. In comparison with saline controls, cosyntropin (0.25 mg/duck) produced a two- to three-fold increase in corticosterone 30 min after administration. Maximal concentrations ranged from 132 to 312 ng/ml and occurred between 1 and 2 hr post-injection. Corticosterone concentrations declined to basal, pre-injection values after 4 hr. Endogenous ACTH release in response to handling stress was evident in control ducks after saline injection but did not interfere with interpretation of the stimulation test. Recommendations for the ACTH stimulation test in black ducks include a 30 min acclimatization period for recently captured or relocated ducks and determination of plasma corticosterone concentration 1 to 2 hr following intramuscular injection with 0.25 mg cosyntropin.

The occurrence of mycoplasmas in selected wild North American waterfowl.

We determined the prevalence of mycoplasma infection in breeding mallard (Anas platyrhynchos) and canvasback (Aythya valisineria) hens and their broods from the central United States (1988 to 1990); and wintering American black duck (Anas rubripes) and mallard hens from the eastern United States (1990 to 1993). Mycoplasmas were isolated by culturing tracheal swabs from 656 live birds and tissue samples from 112 dead waterfowl. Nine (18%) of 51 mycoplasma isolates were identified as Mycoplasma anatis; M. anatis was recovered from four mallards, a black duck, and a gadwall (Anas strepera) duckling. Nineteen (37%) of 51 mycoplasma isolates were identified as Mycoplasma cloacale; these isolates were obtained from mallard, canvasback, and black duck adults, and from a mallard duckling. Additional unspeciated mycoplasmas were isolated from mallards, black ducks, and one canvasback.

Influence of low-level cadmium and reduced calcium intake on tissue Cd concentrations and behaviour of American black ducks

Populations of American black ducks have declined and it has been hypothesized that wetland acidification, which can alter food quality by increasing availability of cadmium and decreasing that of calcium, may have contributed. We tested whether low-level cadmium and reduced calcium intake affect tissue cadmium concentrations and behaviour of captive black ducks. Adults received diets that mimicked cadmium and calcium concentrations in invertebrate prey from acid and from circumneutral wetlands for three spring and summer months in 1991 and 1992. Behaviours were monitored both when birds were fed experimental diets and control (commercial) diets. Cadmium in kidneys and liver differed significantly among groups and low calcium facilitated cadmium uptake. After two breeding seasons, levels of accumulated Cd were not lethal. However, birds that received Cd were significantly more active than control birds. Increased activity may have implications for survival of birds in the wild.

Lead Contamination of Waterfowl in Tasmania by Ingestion of Shotgun Pellets From Duck Shooting.

Shallow-water sediments in duck-shooting areas were sampled to assess availability of shot pellets to foraging waterbirds by determining pellet densities and relating settlement behaviour to particle size composition. Sediments dominated by smaller particle sizes were found to inhibit pellet settlement below the surface layer. Blood samples were obtained from black swans (Cygnus atrata) and more than 17% had elevated lead concentrations. A small number of gizzards from Pacific black ducks (Anas superciliosa) held no pellets, but approximately 50% of livers and bones examined showed elevated lead concentrations. Alternative sources of lead pollution were considered and water and sediment sampling was carried out near the closest highway, but lead concentrations were very 1~w. The lead residues found in birds, and pellet densities in sediments, were broadly similar to those reported for areas with documented lead pellet contamination problems outside Tasmania. This indicates the existence of a lead pellet problem requiring remedial action. Options for this are briefly considered, as is the likelihood of other species being contaminated by direct ingestion of pellets, or indirectly by predation.

Morphometric similarity of Mallards and American Black Ducks

Morphometric data were collected from 347 American Black Ducks (Anas rubripes), and 1466 Mallards (Anas platyrhynchos) taken by hunters in the Lake St. Clair and Lake Erie regions of southwestern Ontario during autumn 1986 and from 511 American Black Ducks shot throughout the province of New Brunswick during the 1988 and 1989 hunting seasons. Discriminant function analyses based on eight external morphometric variables (wing chord, tarsus length, middle toe length, hind toe length, culmen, head length, naris width, and bill width) did not accurately distinguish Black Ducks from Mallards. Discriminant function analyses produced correct classification rates that, averaged over the four age–sex classes, were 61% for Mallards and 71% for Black Ducks. The highest classification rates were from the discriminant function analyses of Ontario Black Ducks and New Brunswick Black Ducks that, averaged over the four age–sex classes, were 74% for Ontario Black Ducks and 80% for New Brunswick Black Ducks. Although our morphometric analyses did not incorporate all morphometric characteristics of Black Ducks and Mallards, they do show that Black Ducks and Mallards collected in eastern Canada are morphometrically very similar.

Habitat use and movements of postfledging American black ducks (Anas rubripes) in the St. Lawrence estuary, Quebec

We used radiotelemetry to determine habitat use and movements of 38 female juvenile American black ducks (Anas rubripes) on the north shore of the St. Lawrence estuary, Quebec, from 28 August to 15 November 1991. Ducks separated into three groups based on habitat use: inland, estuarine, and those using a mixture of habitats. Ducks using mixed habitats used the greatest variety of habitat types, flew the greatest distances and most often between night roosts and day foraging areas, and were unlikely to be shot. The mean distance flown between night-use and day-use areas for all ducks increased nearly 50% after the hunting season began (overall mean = 6104 m, range 1500 – 26 384 m). Mean home range size was 27.6 ± 6.5 (SE) km2. Ducks exhibited stronger fidelity to wetlands used at night than to those used during the day. Ducks that were shot spent a high percentage of their time on the estuary (90.1 ± 7.4%) and exhibited high fidelity to a day-use area before the hunting season (73 ± 7.3%).

Mitochondrial Analysis of Gene Flow between New Zealand Mallards (Anas platyrhynchos) and Grey Ducks (A. superciliosa)

ABSTP,CT.--One of the more well-known examples of hybridization in birds is the frequently documented occurrence between sexually dimorphic Mallards (Anas platyrhynchos) and several closely related nondimorphic species in the mallard complex. In New Zealand, the Grey Duck (Anas superciliosa superciliosa) is the indigenous, nondimorphic Mallardlike species, and extensive hybridization with introduced Mallards has been implicated in the population decline of Grey Ducks. Individuals from throughout the country were classified phenotypically as parentals or hybrids based on variation in plumage, bill color, and leg color. We confirmed species-specific mitochondrial DNA haplotypes by comparing restrictionenzyme fragment patterns in Grey Ducks and New Zealand Mallards to those of Pacific Black Ducks (A. superciliosa rogersi) from Australia and Mallards from North America, respectively. Our data indicate that hybridization has led not only to introgression of Grey Duck mtDNA into Mallard populations (the predicted direction of gene flow), but also to significant introgression of Mallard mtDNA into Grey Duck populations. Thus, the contention that hybridization between Mallards and nondimorphic species involves primarily Mallard males with females of the other species is not upheld for this example from New Zealand. The speciation process appears to be undergoing reversal. Received I April 1993, accepted 2 July 1993. THE INCIDENCE OF interspecific and intergeneric hybridization in the order Anseriformes is higher than in any other order of birds, reaching 30 to 40% by some estimates (Grant and Grant 1992). In addition, a substantial proportion of interspecific hybrids (20%) in this order have been reported to be fertile (Scherer and Hilsberg 1982), so there is potential for extensive gene flow and introgression between some species. Among the more well-known examples is the frequently documented incidence of hybridization between sexually dimorphic Mallards (Anas platyrhynchos) and several closely related, nondimorphic species. For instance, in North America, hybridization with Mallards has been implicated as one factor in the population decline of American Black Ducks (A. rubripes; Johnsgard 1967, Heusmann 1974, Ankney et al. 1987), Hawaiian Ducks (A. wyvilliana; Griffin et al. 1989), and Mexican Ducks (A. platyrhynchos diazi; Hubbard 1977). Increasing numbers of