Suchergebnisse

The breeding of black swans on two nearby lakes, 18 km apart, was documented over a 5-year period.
The lakes differed in physiography and in botanical features. The numbers of swans breeding and the
timing of breeding differed markedly between the lakes and coincided with gross differences and changes
in observed abundance in aquatic plants known to be important as food for swans. Important factors
affecting the selection of nest sites were social factors, security, the presence of an adequate substrate and
of materials to construct a nest, and ease of access to water. Within each breeding season the timing of
laying often differed among nesting colonies on the one lake, apparently reflecting an influence from
social factors in synchronizing breeding within a colony. Breeding success was poor, due evidently to
failure of cygnets to survive in the first weeks after hatching and to desertion of eggs in nests. Failure of
food supplies may be the main cause. The reproductive strategy of the black swan appears to be
essentially opportunistic; the female is capable of laying repeatedly over an extended period, so that eggs
are often produced at times that do not necessarily predict suitable conditions for either the survival of
cygnets or even the completion of incubation.

Aspects of the biology of the black swan were obtained mainly from studies of captive birds. Details
are given on colour and plumage; the distinctive juvenile and adult plumages are described; in adults
iris colour differs between the sexes and is related to weight in both sexes and sexual condition in
males Growth rates vary significantly according to environment. Fledging was at 108-141 days for
captive cygnets but was estimated to extend to 170 days in wild birds. Young birds usually moulted
into adult plumage between August and November at ages of 8-26 months. Replacement of the wing
plumage requires 38-51 days. Periods of 7-36 months elapse between moults of the wing plumage,
the period decreasing significantly wlth age. There is no fixed temporal relationship between breeding
and moulting, though adults often moult within six months of laying, so that they are flightless during
the pre-fledging period of cygnets. Breeding birds tend to moult later in the year and more frequently
than birds not breeding. Birds usually attain sexual maturity and breed at ages of 18-24 or 33-36
months, within 1-2 years of attainment of adult plumage. Captive swans bred in all months of the
year except December and January, with most in June-August. Frequency of laying was variable and
highly dependent on the particular circumstances of captivity. Most swans commenced two or more
clutches annually in at least one year of captivity. Within less than 12 months, a single female was
capable of commencing eight clutches or rearing three broods.

Aspects of behaviour and social organization in the black swan are outlined and discussed. There
is a high degree of flexibility and individualism in social relationships during breeding, which is considered
to be of significance in the ecology of the species.

Statistics are given for egg dimensions, clutch size, laying rate and incubation period in black swans nesting at Lake George and Lake Bathurst, N.S.W., and compared with data from other studies.

Methods of determining clutch size and incubation dates are given and examined. Emphasis is placed on the importance of the method of assessment of clutch size in comparisons within and between studies.

There was evidence of two size classes of eggs, possibly related to factors of age or breeding experience, the smaller class being laid in summer breeding, during an exceptional abundance of food, but not in winter when food may have been limiting. Egg size varied significantly, according to sequence in the clutch. The adaptive significance of egg size is discussed; moisture loss may be
important in the evolution of egg size.

Clutch size varied significantly according to the location and date of nesting. The reasons for the variation were, possibly, both in the nutritional value of the food available and in its relative temporal and physical availability and the swans' abllity to metabolize it. Possible evolutionary determinants of average clutch size in the black swan are considered. Moisture losses from the egg may again he important.

The laying rate was simdar to that reported elsewhere. The mean incubation period was 40.45 days and most clutches ranged from 39 to 43 days.

Clutches laid in autumn and winter took marginally longer to hatch than clutches laid in spring and summer, possibly due to effects of ambient temperature; the difference was probably not of particular adaptive significance.

The first week of the duck shooting season provided the highest rate (33 %) of band recoveries of mountain duck; the rate in subsequent weeks varied between 4.8 and 10.4%.

More birds were recovered on Saturdays (48%) and Wednesdays (16.5%) than on other days of the week.

Two samples of mountain ducks totalling 1001 birds were trapped and banded at Lake George,N.S.W. A highly significant difference in age structure between the two samples, taken in January 1965 and in February 1970, may be related to major differences in rainfall for the year preceding each sample. The sex ratio was markedly biased in favour of females.

Recoveries of birds were nearly all to the south and west and 300-700 km from the banding site.

Fully 99 % of recoveries were in States other than New South Wales.
Examination of one sample of 679 mountain ducks for moult of primary and secondary wing feathers showed that approximately one-third of the adults were moulting. It was concluded that the birds were possibly normal residents of the region in which most recoveries occurred, and that they make an annual moult migration to Lake George.

Regular counts over an 18-month period were made of the water birds of the Alice Springs sewage farm.

Thirty-four species were recorded; the frequency of observation of each species, in terms of percentage of total visits observed, was significantly related to species population size. The counts indicated that the sewage farm probably provided only temporary refuge during movements for most individuals of all species.

Rainfall appeared a major factor affecting the number of species and total population present.

The buildup of mallard and mallard-black duck hybrid populations in Australia has caused concern for the conservation of the black duck.

Mallard populations are shown to be restricted in size and distribution in comparison to those of the black duck. Hybrids could not be confidently identified, other than those that showed obvious plumage characteristics of both species.

Limited field studies in the Sydney district showed the stability of mallard and hybrid populations in comparison to those of the black duck, and there was evidence of restriction of pairing to intraspecific or intrahybrid matings and of poor hybrid breeding success.

At present mallard hybridization per se does not pose a conservation threat to the black duck in Australia. This assessment might not apply under large-scale increase and perhaps husbandry of the feral mallard. In sufficient numbers mallard might threaten populations of the black duck by a different means, competition for refuge in times of drought.

The sexual cycles of two genera of frugivorous rain-forest pigeons, Ducula and Ptilinopus, and two ground-feeding pigeons of the open woodland, Geopelia humeralis and G. striata, have been studied at latitude 9D 29'S. in New Guinea.

In P, iozonus, P. magnificus, G. humevalis and G. striata some males were sexually active and some females had enlarged follicles in each month of the year and so some individuals, at all times, were capable of breeding; there was an indication that this situation was general in the two genera.

In the rain-forest species more birds had enlarged gonads in the late dry season and wet season than at other times. Both sexes of G. stviata had peak gonad size in the late wet and early dry seasons; G. humevalis maintained peak activity throughout the dry season; both species had small gonads in the late dry season.

The cycles of gonad size of fruit pigeons and ground-feeding pigeons corresponded to the
probable cycle of food abundance in the two habitats. There was no evidence of an effect of
photoperiod in Geopelia but it could not be excluded in males of Ptilinopus.

Data collected during clear felling are collated and presented on the distribution of arboreal marsupials in 16 forest vegetation types (FVT) in 7 FVT groups. Eight species were included in the study: Petaurus breviceps, P. australis, P. norfolcensis, Petauroides volans, Acrobates pygmaeus, Trichosurus vulpecula, Pseudocheirus peregrinus and Cercartetus nanus. Most of the individuals reported were in the following 6 FVTs: swamp gum (characterized by Eucalyptus ovata); mountain gum (E. dalrympleana)/manna gum (E. viminalis); peppermint (E. radiata or E. dives); southern blue gum (E. maidenii, E. cypellocarpa or E. nitens); brown barrel (E. fastigata); and brown barrel/gum (E. cypellocarpa, E. nitens, E. maidenii, E. viminalis or E. dalrympleana). The results are discussed in relation to present forest management and forest clearing procedures in the Eden region. Forests about to be cleared for Pinus radiata plantations or for farmland on private property adjacent to State Forests are predominantly of types identified as of high value as wildlife habitat.

[See FA 45, 478-479] Felling crews provided information on the species and number of animals displaced during logging operations in 5010 ha of forest clear felled between May 1980 and Sept. 1981. Overall, 898 individuals of 8 species of glider and opossum were recorded. Geological data were also collected. The data were analysed together with published information on tree species within 22 recognizable communities and NPK concn. in Eucalptus foliage. The fauna tended to be concentrated in communities with Eucalyptus spp. with high nutrient concn. in their foliage. These communities occurred mostly on soils of one geological formation (Devonian intrusives) recognized in the district for the production of highly fertile soils.

Populations of waterfowl of three game species, the Pacific black duck Anus superciliosa, grey teal
A. gibberifrons, and maned duck Chenonetta jubata, were assessed by aerial survey in October 1983
within a survey region of 2 697 000 km2 of eastern Australia. The numbers of each species were
assessed on all surface waters of over 1 ha, and on a sample of smaller surface waters within 10 survey
bands each 30 km wide and spaced at intervals of 2� latitude from 20�30' to 38�30'S. The area within
the survey bands was 324 120 km2, which gave a sampling intensity of 12.0% of the land surface area.
The area of features shown as wetlands or water impoundments within the survey bands on 1 : 2 500 000
topographic maps was 19 200 km2 or 11.2% of the total area of these features in the survey region.
The area of surface waters surveyed was assessed at 465 300 ha. Assessments of populations of each species
were tallied for wetlands by grid cells of 6 min of 1� longitude along the survey bands (258-309 km2
depending on latitude). Distributions were then mapped, with log*10 indices of populations in each cell.
Distributions of the black duck and grey teal showed a pattern of intense aggregation in limited numbers
of cells, that of the maned duck was more evenly distributed. The major concentrations of the Pacific black
duck were recorded in northern New South Wales and the south-eastern, western, central eastern and
central coastal regions of Queensland; those of the grey teal were in south-western, western and northern
New South Wales and central-eastern Queensland; the maned duck was broadly distributed over inland
New South Wales with the exception of the far west, inland southern Queensland, and central northern
Victoria.