Suchergebnisse

We can use aerial surveys of waterbirds to identify high-conservation-value wetlands, estimate species' abundance and track changes in wetland condition. Two major approaches prevail. Transects to estimate a few species (1–20, often ducks) are predominantly used in North America and counts of entire waterbird assemblages on discrete wetlands are favoured in Australia. Such differences reflect wetland type, discrete (whole count) and continuous (transect) sampling, different objectives and history. There are few continuous large-scale aerial surveys of waterbirds, despite cost efficiencies and effectiveness. We review the eastern Australian waterbird survey that samples about one-third of the continent (2.697 million km2). Each October, during 1983–2007, all waterbirds were estimated on an average of 811 wetlands, within ten 30-km-wide survey bands, separately extending across latitudes from the east coast to central Australia. The survey has demonstrated the importance of arid wetlands for waterbirds and provided management data on distribution, abundance and breeding of waterbirds. Most significantly, long-term temporal data for individual wetlands provided strong evidence for the impacts of water resource development (dam building, diversion of water). These data have influenced wildlife management, river rehabilitation and restoration policies at a national scale.

Abstract
We compared diets of marabou storks Leptoptilos crumenifer foraging from urban landfills and natural areas in northern Botswana using stable isotope analyses and inductively coupled plasma mass spectrometry on moulted feathers. There were significant differences in the diet of marabous foraging from natural areas compared to urban waste sites, reflected by lower δ13C and less enriched δ15N concentrations in those feeding at landfills, suggesting a shift in trophic niche. Feathers from birds foraging at landfills also had significantly higher concentrations of chromium, lead, nickel, and zinc and lower levels of cadmium and potassium than feathers sampled from natural areas. We also analysed marabou regurgitant (42 kg, naturally expelled indigestible food resources) from the Kasane landfill site. More than half was plastic, with single regurgitants weighing up to 125 g. Urban waste stored in open air landfills is altering some marabou diets, affecting their natural trophic niche, resulting in the consumption (and regurgitation) of large amounts of plastic, and exposing marabou to potentially chronic levels of trace metals. Despite the marabou's apparent resilience to this behavioural shift, it could have long-term effects on the population of the marabou stork, particularly considering Botswana has some of the few regular marabou breeding colonies in southern Africa.

We examined the relationships between abundance of 16 species of waterbirds
and the rainfall in eastern Australia, the rainfall west of this region, the
annual Southern Oscillation index (SOI), the wetland area, and hunting in
eastern Australia for the period 1983–92. Data were collected during
aerial surveys of eastern Australia. For most explanatory variables, lags of
up to five years before aerial surveys were also investigated during these
analyses. The analyses covered all nine game species (plumed whistling-duck,
Australian shelduck, Australian wood duck, pink-eared duck, grey teal,
chestnut teal, Pacific black duck, Australasian shoveler, hardhead) and seven
non-game species (Australian pelican, white-faced heron, yellow-billed
spoonbill, freckled duck, black swan, black-winged stilt, red-necked avocet).
Regression models were developed for all species apart from Australian
pelicans. Rainfall and climate indices generally were most correlated with the
species' abundance. Bonferroni adjustments to significance levels meant
that there were significant variables in regression models for seven of the 16
species. Abundance indices for plumed whistling-duck, chestnut teal, hardhead,
black swan and black-winged stilt were related to the climate variables
(rainfall, SOI) and wetland area, whereas abundance of pink-eared duck and
red-necked avocets were negatively related. Abundance of chestnut teal was
positively related to numbers of hunting licences sold. The results are
equivocal about the role of hunting in determining waterfowl abundance, which
is probably a reflection of few data points and numbers of variables included.
In general, abundance indices of waterbirds appear to have decreased between
1983 and 1992, which may correspond to other factors not modelled