Suchergebnisse

The effectiveness of a baiting campaign against red foxes
(Vulpes vulpes) was investigated in a rangeland area
near Carnarvon, Western Australia. An area of 3180 km2
was aerially baited with dried meat baits containing 3 mg 1080 poison (5 baits
km–2) in August 1995. All 45 radio-collared foxes
monitored in the area were killed by baits. More than half the radio-collared
foxes died within 3 days of baits being laid; the last surviving
radio-collared fox died 44 days after baits were laid. The overall population
reduction was estimated to be >95%. Further implications of this
high level of bait uptake are discussed in relation to immunocontraceptive
control of foxes, as well as for population reduction or vaccination of foxes
to control rabies.
Reinvasion of the baited area occurred mainly in autumn, when juvenile foxes
were dispersing. The relevance of this result is discussed in relation to
developing more effective baiting strategies. As part of another experiment,
outer sections of the baited area were periodically re-baited as a buffer zone
to reduce immigration by foxes into the central baited area; the buffer
baiting proved to be very effective in preventing recolonisation of the entire
baited area.

Intensive destructive sampling of a population of red foxes
(Vulpes vulpes) was undertaken over an area of 200
km2. A total of 204 foxes, estimated to be 94% of
the total population on the site, was collected. Population density was
0.46–0.52 adult foxes km–2. Sampling was
carried out in December, when young of the year were present and when data on
female productivity could be obtained from counts of placental scars.
Life-table analysis for vixens revealed that mortality was greatest for those
aged 0–16 months and those older than 3 years. Average mortality of
adult vixens was 39%. Adult vixens (n =
47) had an average (s.e.) of 3.7 0.3 placental scars; 8.5% of vixens
failed to breed. The number of placental scars did not vary significantly with
age. Various hypothetical scenarios were used to identify which social
system(s) may have been operating in the area. Predictions of vixen
productivity and cub mortality were compared with observed reproductive data
and the actual number of cubs collected. The scenario that best matched the
observations was a simple mated pair system. Pure dominance hierarchies were
unlikely to have occurred. The implications of the findings are discussed in
relation to the ability of foxes to overcome natural or artificially-imposed
population reduction. It was estimated that under a fertility control regime,
>45% of vixens would need to be sterilised before the fox population
would begin to decline.

The acceptability of three types of non-toxic predator baits to a variety of indigenous non-target species was determined in the laboratory. The bait-types tested were: Dried Meat Bait (DMB), Probait and two sizes of FoxOffTM baits (30 g and 60 g). The potential poisoning risk, if the baits had been toxic, was calculated for each species from their consumption of non-toxic bait and their sensitivity to 1080. Three species consistently sampled baits; Dasyurus geoffroii, Trichosurus vulpecula and Rattus fuscipes. Where species have had exposure to fluoroacetate-bearing vegetation, their consumption of bait and their level of tolerance to 1080 was such that only 2 of 15, 4 of 15, and 3 of 6 species were considered to be potentially at some risk from toxic DMBs, Probait, and FoxOffTM baits, respectively. In contrast, and mainly because of their lower tolerance to 1080, the theoretical risk for those species without evolutionary exposure to fluoroacetate-bearing vegetation was such that 6 of 12, 8 of 12, and 8 of 9 species theoretically face a high or moderate risk from 3-mg DMBs, Probait, and FoxOffTM baits, respectively. We emphasise, however, that theoretical risk does not necessarily equate to a practical risk, and these results are best used to determine which non-target species should be monitored at the population level during predator-control operations. Factors affecting the potential risk to non-target indigenous animals, and some cautions when extrapolating data from laboratory-based studies to the field situation, are discussed.