Suchergebnisse

The extent of organochlorine pesticide contamination in 3 species of predatory birds from the central regions of South Australia was investigated. Residues in both eggs and tissue, as well as measurements of shell thickness, were obtained for Falco peregrinus (peregrine falcon), Pandion haliaetus (osprey) and Haliaeetus leucogaster (white-bellied sea eagle). Organochlorine residues in some prey species were also measured. Residues of DDE and DDT in the predatory birds were found to be low to moderate. Concn of total DDT were greatest in F. peregrinus (mean 1.82 mg/kg), followed by the H. leucogaster and P.haliaetus (mean 1.07 and 0.11 mg/kg, resp.). A comparison of F. peregrinus eggs collected before and after 1947 showed significant eggshell thinning (mean 16%). DDT residue levels of concern were recorded for several prey species commonly found in the diet of H. leucogaster and F. peregrinus, particularly in Columbia livia (feral pigeons) (37.46 mg/kg) and Larus novaehollandiae (silver gulls) (3.06 mg/kg). These concn were well above those known to cause reproductive failure in falcons. DDT was also found at high concn in eggs of Pelecanus conspicillatus (pelican) (mean 2.04 mg/kg). Dieldrin was present in most samples, but at low concn. The degree of pesticide contamination detected was considered sufficient to interfere with the reproduction of F. peregrinus in South Australia.

The diet of nestling rainbow bee-eaters, Merops ornatus, was determined by analysis of droppings and
regurgitated pellets collected at one site on Rottnest I., W.A. in the summer of 1982/83, and five sites
in the summer of 1983/84. In total, 2187 insects from 10 families were identified. These comprised:
Hymenoptera (95%), including Scoliidae (14%), Tiphiidae (38%), Sphecidae (l8.5%), Apoidea (1%),
Formicoidea (7.5%) and undetermined Hymenoptera (16%); Coleoptera, Buprestidae (1.5%); Diptera,
Muscidae (<1%); Hemiptera (3%); Odonata (<1%); and Orthoptera (<1%). The relative proportions
of the different prey types varied significantly between sites and between different sampling times at
the same site. There were also site-related differences in the mean length of nestling prey and at three
sites nestlings were fed different sizes of prep during their development. Estimates of prey length based
on wing remains were significantly smaller than those based on head remains at four of the six sites,
and shapes of prey length distributions based on wings and heads were significantly different at all
six sites.

The effect of rabbit control methods on rabbit populations and subsequent changes in vegetation were
assessed over 2 years on a calcareous shrubby grassland in central Australia. Warren ripping and
fumigating decreased mean population levels to four rabbits per kilometre of spotlight transect, and
1080 poisoning decreased mean levels to 9 km-1, compared to the untreated levels of 20 km-l. Release
of European rabbit fleas did not have any significant effect on rabbit populations. In the untreated rabbit
populations, 68% of the fluctuation in numbers was accounted for by total rainfalls in the previous
summer and the previous winter, and by a forage greenness rating. Experimental control of rabbits
combined with exclosures indicated that grazing by high numbers of rabbits reduced the frequency of
Enneapogon spp. at one site whereas levels rose in all other sites during the two years of good rainfall.
The frequency of several species, such as Chenopodium cristatum, Phyllanthus rhytidospermus and
Portulaca oleracea, was highly correlated with rabbit density in the previous year, suggesting that rabbit
grazing promotes their increase. Grazing'by rabbits alone depressed standing biomass in the following
season by 300 kg ha-1 from a maximum 1200 kg ha-1 within the exclosures. Cattle grazing further
decreased biomass by 150 kg ha-1. Seedlings of Acacia kempeana were almost absent in those areas
open to rabbit grazing, but they were reasonably dense where rabbits were excluded. However, the
vegetation response over the 2 years of experiment was due mainly to seasonal changes rather than
rabbit control, and does not justify the expense of rabbit control at this stage. Substantial improvement
in vegetation composition over the longer term may alter this conclusion.

Nine wild dogs, Canis f. familiaris, radio-tracked over periods of 28-61 days in Kosciusko National Park,
N.S.W., occupied home ranges of 220-5420 ha (mean 2193 ha). These home ranges were similar in size
to those observed for dingoes, C. f. dingo, in other areas of south-eastern Australia. The maximum
distance that any of the nine dogs moved between successive daily locations was 11.2 km. On the basis
of this information and that obtained by others, we suggest that the control of wild dogs on Crown
Land in south-eastern Australia should be confined to those areas adjacent to private grazing land.
Furthermore, a control zone 12-20 km wide should be adequate.
Two successive trail-baiting campaigns with 1080 poison in March and April 1982 killed only two
(22%) of the nine wild dogs carrying radio transmitters. Traps, in comparison, caught 15 out of 27 (56%)
of the dogs known to be in the area. The main factors which reduced the success of the poisoning
campaign were the rapid loss of toxicity of the baits after their distribution, the rapid rate at which
they were removed by other animals, particularly foxes Vulpes vulpes and birds, and the dogs' apparent
preference for natural prey.