Magpie Goose Anseranas Semipalmata Research Articles

Using dietary metabarcoding analyses to characterise waterbirds–agriculture interactions

Abstract Globally, the use of agricultural fields by waterbirds has increased, resulting in conflicts with farmers. Designing effective management strategies to resolve these conflicts requires understanding the species' resource use. Dietary analyses can shed light on the extent of consumption of agricultural crops and surrounding natural resources, as well as the potential relationship between diet and an individual's body condition and ultimately its fitness. We examined the dietary composition of the tropical magpie goose Anseranas semipalmata, seasonally utilising a mixed natural‐agricultural landscape of northern Australia. We used DNA metabarcoding of intestinal contents from hunted geese to reconstruct individual diets and evaluated body condition from morphometric measurements. We compared the relative contribution of agricultural and natural foods to dietary composition, and investigated how this contribution varied spatially, temporally and among individuals that differed in body condition. We found that geese consumed both agricultural and naturally occurring plants assigned to at least 35 taxa. The most frequent and abundant taxa belonged to three families: Poaceae (grasses), Cyperaceae (sedges) and Anacardiaceae (mangoes). Dietary composition varied substantially among sampling sites and over time but not with body condition of geese. Synthesis and applications. We used a novel approach to investigate the diet of a waterbird perceived as problematic across an agricultural landscape in tropical Australia. We showed that individuals forage opportunistically, and that agricultural crops, while eaten, may not represent an essential part of geese diet across the study region. The knowledge acquired provides new insights into the species' foraging ecology offering clear alternatives for mitigating goose–agriculture interactions. Providing disturbance‐free alternative foraging areas or minimising the attractiveness of targeted agricultural fields (e.g. shorter grass, alternative ground cover) may alleviate crop consumption while benefiting the species' long‐term conservation. While also highlighting the limitations of DNA metabarcoding, our dietary study emphasises the potential of this methodology to improve our understanding of crop damage by wildlife, allowing effective evaluation of management requirements.

Biogeographic models of gene flow in two waterfowl of the Australo-Papuan tropics

There are many large, easy-to-observe anseriform birds (ducks, geese, and swans) in northern Australia and New Guinea and they often gather in large numbers. Yet, the structure of their populations and their regional movements are poorly understood. Lack of understanding of population structure limits our capacity to understand source-sink dynamics relevant to their conservation or assess risks associated with avian-borne pathogens, in particular, avian influenza for which waterfowl are the main reservoir species. We set out to assess present-day genetic connectivity between populations of two widely distributed waterfowl in the Australo-Papuan tropics, magpie goose Anseranas semipalmata (Latham, 1798) and wandering whistling-duck Dendrocygna arcuata (Horsfield, 1824). Microsatellite data were obtained from 237 magpie geese and 64 wandering whistling-duck. Samples were collected across northern Australia, and at one site each in New Guinea and Timor Leste. In the wandering whistling-duck, genetic diversity was significantly apportioned by region and sampling location. For this species, the best model of population structure was New Guinea as the source population for all other populations. One remarkable result for this species was genetic separation of two flocks sampled contemporaneously on Cape York Peninsula only a few kilometers apart. In contrast, evidence for population structure was much weaker in the magpie goose, and Cape York as the source population provided the best fit to the observed structure. The fine scale genetic structure observed in wandering whistling-duck and magpie goose is consistent with earlier suggestions that the west-coast of Cape York Peninsula is a flyway for Australo-Papuan anseriforms between Australia and New Guinea across Torres Strait.

Wetland conservation and sustainable use under global change: a tropical Australian case study using magpie geese

Imminent shifts in environmental parameters due to climatic change might have profound ramifications for wetlands listed under the Ramsar convention. Although the exact mechanisms by which global change will affect these systems are not known, models that simulate component drivers, particularly at a broad spatial scale, can nevertheless allow for more informed conservation decision making. Such general inference is particularly needed for wetlands across the tropics, where less knowledge and fewer resources are available to mitigate the impacts on important conservation sites. Here we develop a case study of wetland loss to sea level rise across tropical north Australia (including Ramsar‐listed sites), and link these to a metapopulation model for a keystone endemic waterbird, the magpie goose Anseranas semipalmata. We projected published models on sea level rise through to the year 2400, and found a non‐linear trajectory of inundation up to 20 m above present levels. Digital elevation models were used to simulate sea level rise and the spatially differentiated loss of wetland habitat used by geese. Range retraction was linked to decline in ecological carrying capacity, and we coupled wetland‐specific habitat loss projections to a spatially explicit demographic metapopulation model. Additionally, we included alternate harvest strategies based on present‐day estimates of indigenous and non‐indigenous offtake of geese, and examined the synergy between wetland loss and hunting on extinction risk. Our results suggest that Australia's once‐abundant and widespread magpie goose will be reduced to a fragmented population of just a few thousand individuals within the next 200–300 yr. Harvest could continue for some time, up to a “tipping point” at around 5% loss of current wetland habitat, after which the decline of geese is rapid. Given the inexorable nature of sea level rise, short‐ to medium‐term conservation of waterbirds across Ramsar wetlands must prepare for adaptive wetland management, such as through buffer‐placement, and ongoing monitoring of harvest.

Climate Change Enhances the Potential Impact of Infectious Disease and Harvest on Tropical Waterfowl

ABSTRACTGlobal warming exacerbates threats to biodiversity as ecological systems shift in response to altered climatic conditions. Yet the long‐term survival of populations at direct risk from climate change may also be undermined by local factors such as infectious disease or anthropogenic harvest, which leave smaller and more isolated populations increasingly vulnerable to the rapid pace of global change. We review current and future threats to an exemplar tropical waterfowl species, magpie geese Anseranas semipalmata, and focus on the potential synergies between infectious diseases, harvest, and climate change. We outline viral, bacterial, and fungal pathogens likely to cause disease in geese, and give mention to parasites. Further, we elaborate on a previously developed, spatially explicit population viability model to simulate demographic responses to hunting and novel or enhanced disease outbreaks due to climate change. With no harvest, the simulated disease epizootics only threatened metapopulation viability when both mortality rate was high and outbreaks were regular (a threshold response). However, when contemporary site‐specific harvest is included as an additive impact, the response to disease severity and probability was linear. We recommend field research to test these hypotheses linking drivers of waterfowl population decline to disease–climate change interactions.

An Oligo-Miocene magpie goose (Aves: Anseranatidae) from Riversleigh, northwestern Queensland, Australia

ABSTRACT The magpie goose Anseranas semipalmata (Aves: Anseranatidae), the sole modern representative of the family, is endemic to Australia. The fossil record of Anseranatidae in Australia was until now restricted to Pliocene and younger sediments. Here we describe an anseranatid from the Oligo-Miocene Carl Creek Limestone in the Riversleigh World Heritage Property, Boodjamulla (Lawn Hill) National Park, in northwestern Queensland, as a new species and genus, based on a coracoid and two scapulae. These fossils extend the known age of the Anseranatidae lineage in Australia to about 25 million years ago. The fossil distribution of Anseranatidae now includes the Paleocene in North America, Eocene and Late Oligocene of Europe, and the Late Oligocene to earliest Miocene in Australia, indicating a globally widespread distribution of the family during the early-mid Tertiary.

Nesting phenology of magpie geese (Anseranas semipalmata) in monsoonal northern Australia: responses to antecedent rainfall

AbstractThe density of nests of the magpie goose Anseranas semipalmata on the Mary River floodplain fluctuated markedly during 1988–93, failing almost completely in unfavourable (El Niño) years. Nest density and timing of nesting were strongly correlated with variations in the time of onset of the wet season, but were much less sensitive to rainfall quanta in the mid‐ to late wet season. Nest densities were higher and nesting was initiated earlier in breeding seasons preceded by sustained rainfalls during the transition from dry to wet seasons. Clutch sizes were slightly larger in years of early wet‐season onset. Within seasons, later clutches contained fewer eggs and the eggs were smaller, probably as a consequence of later nesting by younger birds. Second clutches from a small sample of marked re‐nesting birds and a pulse of nesting after flooding losses, contained similar numbers of eggs to first clutches, but the eggs were larger. Dependence of nesting on events occurring months before clutch initiation, when birds are using habitats distant from nesting colonies, illustrates the importance of integrated management of floodplain systems to meet year‐round habitat needs, and the risks posed by homogenization of wetlands by improvement of pasture for grazing.

Aspects of the Nesting Biology of the Magpie Goose Anseranas semipalmata: Incubation Period, Hatching Synchrony and Patterns of Nest Attendance and Defence

SummaryThe period between clutch initiation and departure of family groups from successful Magpie Goose nests ranged from 31 to 33 d. Incubation period was 25 days and family groups remained at the nest up to 4 d after the first egg hatched. Hatching was poorly synchronised relative to many other waterfowl, probably due to variable but often elevated egg temperatures (up to 36.6°C) during the 5–10 d laying period. During daytime visits by observers in a motorised airboat, many birds performed displays of various kinds including elaborate decoys, threat postures involving approach to the observer, and less frequently attacks with bill, wings and feet. Males were more often encountered at nests than females. Males more often engaged in aggressive, presumably higher-risk behaviours. Responses involving close approach to the observer were more frequently observed during later phases of incubation, when birds that did not display also permitted closer approach and retreated shorter distances. Females were more likely to be encountered at the nest during the laying period and again around the time of hatching. Consistent with the patterns of daytime encounter, continuous remotely logged (radio telemetry) observations of nest attendance of two birds suggest that males incubate principally during daylight and females nocturnally, but this temporal segregation weakens near hatching. No significant association was found between frequency of nest protecting behaviours (decoy, threat or attack) among attending birds and ultimate nest success. A number of observations at nests attended by marked birds indicated that some nests were incubated or defended by more than one male, confirming observations in semi-captive flocks.

An experimental study of the impact of feral swamp buffalo Bubalus bubalis on the breeding habitat and nesting success of magpie geese Anseranas semipalmata in Kakadu National Park

The impact of buffalo Bubalus bubalis grazing and trampling on magpie goose Anseranas semipalmata breeding habitat and nest numbers was studied over nine wet seasons (1980–1988) at Kapalga within Kakadu National Park. Aerial photographs provided data to compare nest densities within six vegetation types in an area where buffalo grazed throughout the study with an area where buffalo were removed midway through. Buffalo had no significant effect on the abundance or distribution of vegetation types important to geese for breeding. However, high densities of buffalo suppressed the growth of several other species, particularly the grass Hymenachne acutigluma which increasingly displaced the deep water spike-rush Eleocharis sphacelata after buffalo were removed. The annual number of nests fluctuated between 7 and 2028, apparently in response to rain. Most nests were built in the spike-rush/wildrice Eleocharis spp./ Oryza rufipogon association (71%) and in E. sphacelata (20%). Buffalo trampling and grazing influenced the location of nests but not number. After buffalo were removed, more nests were built in deep water areas at the forest edge of the floodplain.

Sex and Age Related Variation in Foraging Strategies of Magpie GeeseAnseranas semipalmata

The Magpie Goose Anseranas semipalmata shows substantial sexual dimorphism in body size, with males being 34% heavier. In at least one habitat (homogeneous sedge swamps) this dimorphism appears to be associated with slight divergence in foraging niche. The size distribution of Eleocharis dulcis tubers ingested by Magpie Geese is similar to their availability in swamp sediments, but there are substantial differences between sexes and suggestions of variation between age groups. Males take more of the larger tubers than females, and juvenile (first-year) birds may ingest a greater proportion of small tubers than birds more than one year old. We suggest that this divergence arises through a mix of size, social and behavioural factors. Within family groups larger males may gain prior access to undisturbed foraging sites, and be better able to exploit cues to tuber size that may be associated with deeper-rooted larger plants. Juveniles accustomed to foraging for seeds in breeding areas may be slow to adopt their parents' foraging strategies after moving to dry season habitat.

Patterns of Egg Laying and Variation in Egg Size in the Magpie Goose Anseranas semipalmata: Evidence for Intra-specific Nest Parasitism

The precocial Magpie Goose Anseranas semipalmata nests colonially on seasonally inundated floodplains, producing a large conspicuous nest. As predicted from the hypotheses of Rohwer & Freeman (1989) regarding the ecological correlates of intraspecific nest parasitism, nests are parasitised by conspecifics. Criteria based on laying rates and sequences classed 35% (n = 22) of closely monitored nests (n = 63) as parasitised. Criteria were conservative, but interpretation is complicated by variable mating arrangements including a preponderance of trios comprising one male and two females. Parasitism rates may have been increased by rising water levels which resulted in flooding of most nests after about one third of the incubation period. Mean clutch size in nests classified as parasitised (10.9 ± 2.3 [s.d.]) was significantly greater than apparently unparasitised nests (8.5 ± 3.1). Parasitic eggs were similar in size and shape to other eggs in parasitised clutches. Clutch size, within-clutch variation in egg dimensions and degree of staining are unlikely to identify parasitism reliably. Improved assessment of the incidence and ecological importance of intra-specific nest parasitism in the Magpie Goose requires further study employing a combination of biochemical and observational techniques.

Lead-Poisoning in Magpie Geese Anseranas-Semipalmata From Ingested Lead Pellet at Bool-Lagoon-Game-Reserve (South-Australia)

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Polygyny in Barrow's Goldeneye

Polygyny in Barrow's Goldeneye

THE ORIENTATION OF PECKING IN VERY YOUNG MAGPIE GEESE ANSERANAS SEMIPALMATA

SummaryThe goslings of the Magpie Goose Anseranas semipalmata make co‐ordinated pecks about 40 min. after hatching. The intensity of pecking is greater by day than by night and also increases with increasing age in unfed goslings. In a series of experiments goslings tended to orientate their pecks towards high, light, green and yellow objects rather than low, dark, blue or red ones, but did not discriminate between rough and smooth objects. It is suggested that these generalized orientation tendencies suffice to direct the goslings' pecks towards potential food, the seed heads of swamp plants. A more precise innate orientation, such as is found in some gull chicks, would not confer greater protection from predation than the shelter of the breeding swamp itself provides, and might prevent the goslings from exploiting some of the available food.