Suchergebnisse

Factors affecting the success rate of traps for catching feral pigs inhabiting a tropical habitat in the
Northern Territory, Australia, were identified by constructing a generalised linear model relating capture
rates of pigs to environmental variables. Capture rates were influenced most significantly by time of
year, being highest during the late dry season and lowest during the late wet season. The next-most
important variables were the presence of fresh pig-tracks at the trap site before construction, and
vegetation type, with capture rates higher in closed forest, open forest and woodland habitats than in
open woodland and low open woodland habitats. Other variables that significantly influenced capture
rates were whether pigs had previously eaten bait at the trap site, presence of rooting, bait type, and
distance from water. The model developed here provides a useful framework of planning and conducting
feral pig trapping programmes in the Northern Territory and other similar tropical habitats.

Employed mark-recapture techniques to monitor trends in the population density of feral pigs in a tropical woodland habitat containing cereal crops, and compared density indices in this habitat with other similar habitat not containing cereal crops. Over the duration of this study there was no significant trend for increase or decrease but population density fluctuated seasonally between 2.2 and 3.5 pigs kg-2 in the woodland site containing cereal crops. A numerical response model was developed relating observed exponential rate of increase of feral pigs to antecedent rainfall. The model estimated the maximum exponential rate of increase (rmax) of feral pigs to be 0.065 plus or minus 0.17 (s.e.) month-1 or 0.78 plus or minus 0.21 (s.e.) year-1. Comparison of indices of population density of feral pigs in woodland habitat with cereal crops and similar woodland habitat without cereal crops demonstrated that the presence of intensive cereal cropping increased population density of feral pigs almost 4-fold. Population density in the woodland habitat without cereal crops was estimated to be 0.8 pigs kg-2. The response to rainfall and the variation in density in response to an increase in the amount of available food is interpreted as evidence that feral pig populations are limited primarily by food availability.

The effectiveness of a small team of hunting dogs for removing feral pigs was examined in
relation to group size of feral pigs encountered and the population density of pigs being hunted.
Hunting dogs were successful on 88% of occasions of catching or cornering solitary pigs when
encountered. This rate of success rapidly declined as the group size of encountered pigs increased,
with the mean maximum number of pigs that could be caught or cornered in any one encounter
estimated to be about one pig per dog. The sex ratio of mature pigs obtained from a hunted
sample showed a significant bias ( X*2 = 4.3,d.f. = 1, P< 0.05) towards catching more males
(M: F = 1.6: 1.0). One team of hunting dogs removed 22 of an estimated 79 pigs inhabiting a
94-km*2 area at a rate of 0.6 pigs h-*1 in 35 h of hunting. It is concluded that hunting with dogs
is an effective way for removing residual pigs after densities have been reduced by other forms
of control.

Common brushtail possums (Trichosurus vulpecula) act as
a reservoir of bovine tuberculosis (Mycobacterium bovis)
in New Zealand and the simultaneous sharing of dens may result in the
transmission of Tb between possums. The effect of manipulating population
density on the per capita probability of simultaneous
den-sharing among possums was investigated at a site near Dunedin, New
Zealand. Den characteristics that could affect the probability of simultaneous
sharing were also investigated, though none were found to be significant. The
daily probability of a possum sharing a den was estimated to be 0.07 for
possums denning within uncontrolled areas of the study area. Den-sharing was
most common between female pairs, though sharing was also recorded between
male–female and male–male pairs. The highest number of possums
recorded sharing a single den was four. Reducing population density
significantly lowered the probability of possums simultaneously sharing dens
within the study area, with greater than 60% reductions estimated to
eliminate simultaneous den-sharing altogether. The relationship between the
contact rate arising from den-sharing and population density was convex-down,
rather than convex-up, as often hypothesised for animal–animal disease
contact processes. The implications of simultaneous den-sharing for the
transmission and control of bovine tuberculosis in brushtail possum
populations are discussed.