(1) Aerial survey methods for estimating
population size of feral water buffalo in northern
Australia were examined.
(2) Line transect models underestimated population
size. Of six models tested the most accurate
underestimated by nearly half. The models give
biased estimates most probably because not all
animals on the survey line were sighted .
(3) Aerial strip transect surveys were also
negatively biased. The extent of this bias was
estimated in index-removal experiments.
Experiments were carried out on two populations in
areas of differing obstructive canopy cover.
(4) In woodland habitat with a canopy cover of 30-
60%, a correction factor of 3.2 was required to
take account of animals not seen. In forest
habitat with a canopy cover of 60-100%, a
correction factor of 4.9 was required.
(5) Using these results, the population size of
feral buffalo, cattle and horses in Kakadu National
Park was estimated by aerial survey at the end of
each year over 6 years. Annual rates of increase
for three regions of the Park were estimated,
taking into account known removals from the
population. The effects of dry season rainfall and
population density in the preceding year on rate of
increase were examined for each species.
(6) The mean annual exponential rate of increase
for each species was 0.10 yr-1 for buffalo, 0.23
yr-1 for cattle and -0.14 yr-1 for horses.
(7) The annual rates of increase varied greatly
between years within all species and were highly
correlated with dry season rainfall in the year of
survey for buffalo and cattle but not for horses.
(8) No significant effect of preceding density on
rate of increase was found for any species. A
large reduction in buffalo populations did not
correspond with an increase in unharvested
populations of horses, suggesting the two species
do not compete for food or other resources.
(9) A campaign to control populations of feral
water buffalo in Kakadu National Park was assessed.
Between 1979 and 1988, approximately 79,000 animals
were removed, 54% by commercial live-capture, 35%
by shooting from helicopters and 10% by shooting
from the ground.
(10) In the period 1983-1988 when population
estimates from aerial survey are available, mean
buffalo population density was reduced from
5.60 km-2 to 1.17 km-2 over the surveyed area of
the Park.
(11) The costs of removal by shooting from
helicopters, capturing animals alive and shooting
from the ground were compared. The mean costs per
animal in 1988 were $24.13, $74.53, and $86.02
respectively.
(12) The effects of initial density and time spent
shooting on number of animals removed by shooting
from helicopters were examined. One linear and two
curvilinear models were fitted to data from four
different removal exercises. The relationship
between time spent shooting and number removed was
best described by a curvilinear (Ivlev) function.
This model was used to estimate costs of control to
a specified density.
(13) Model regression coefficients differed
between removal exercises, suggesting that the
number removed may be affected by variables other
than time spent shooting and initial density. Data
from the range of conditions encountered during
removal is thus likely to be required for robust
estimation of removal costs.
| Identifer | oai:union.ndltd.org:ADTP/219335 |
| Date | January 1990 |
| Creators | Skeat, Andrew, n/a |
| Publisher | University of Canberra. Applied Science |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Andrew Skeat |
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