Baiting with sodium monofluoroacetate (1080) to protect lambs (Ovis aries)
from red foxes (Vulpes vulpes L.) has become more frequent in NSW and other parts
of Australia during the last 10 years despite the lack of reported evidence evaluating
the effects of fox baiting on lamb survival. NSW Agriculture has developed fox
control recommendations aimed at minimising impact, but these guidelines have not
been tested experimentally. Defining the extent of a pest problem and the
effectiveness of pest control are key components of a strategic approach to vertebrate
pest management as it is the damage of pests that justifies their control.
This thesis describes an experimental evaluation of the recommended practice
of fox control in NSW. The effects of three levels of fox control were tested in the
experiment; no treatment, baiting once a year before lambing (the recommended
practice) and baiting three times a year (thought to be the maximum farmers would
instigate). Each treatment had two replicates. No previous manipulative experiment
using synchronous controls and matched replicates has been undertaken to test the
effects. The study quantifies the level of fox predation on healthy lambs and the level
of predation on lambs that had other causes including illness and mismothering
contributing to this fox predation. It also examines the response of the fox
population, lamb predation and lambing outcomes to different levels of fox control.
The cost effectiveness of fox control is examined in relation to lamb predation and an
investigation of the optimum level of fox control is begun. The experiment also
provides the first chance to consider the examination of multiple response variables
and the scale of field ecology experiments required to recognise a significant response
and avoid a Type II error due to between replicate variability even with tightly
controlled site selection criteria to standardise experimental sites, and with the
synchrony of experimental control and treatment surveys.
The study occurred on five sheep properties near Boorowa (34°28'S,
148°32'E) and Murringo (34°18'S, 148°3 1'E) in south-eastern Australia. The terrain
was undulating to hilly with a maximum elevation of 660 m above sea level. The main
agricultural enterprises in the district are Merino wool, fat lamb and beef cattle
production and winter cereal cropping. The native vegetation of Eucalyptus
woodland has been mostly cleared, though remnant patches occur. Most of the area
is now sown with pasture of Phalaris tuberosa, Lolium spp. and clover Trifolium
spp.. The experimental properties grazed self-replacing Merino flocks, primarily for
wool production, so lamb survival was vital to the economic operation of the farm.
Over 50 selection criteria including lamb survival rates, ewe fertility and bloodline,
sheep management practices, climate and habitat features that affect lamb survival,
past fox control practices and prey species were used to select sites Sites were
representative of most sheep farming properties in the region, but were also extremely
similar in factors that affected fox abundance and ewe and lamb survival, thus
minimising variation between replicate sites.
The manufactured meat baits used to poison foxes contained 3 mg of sodium monofluoroacetate (compound 1080). A replacement baiting program was carried
out in 1995 and 1996. Fox control programs were carried out over the experimental
units and adjacent buffer zones covering approximately two fox territories,
approximately 6km2, around the lambing paddock under study. The recommended fox
control practices described by NSW Agriculture also included neighbouring farmers
taking part in an extended group baiting program. In all the area baited at varying
intensities totalled 3400 km2. Synchronised lambing with neighbours was a further
recommended practice to reduce fox predation and was carried out on these sites.
Lambing occurred during a six to eight week period in late winter on all sites, a
practice known as 'spring lambing', and on many surrounding properties so a surplus
of lambs was available to foxes over a relatively short time.
The benefits of fox control were measured directly as enhanced lamb survival
derived from differences in lamb marking rates between ultrasounded flocks of
approximately 1000 ewes and the predation of lambs was measured from over 2000
lamb carcases post-mortemed in 1994, 1995 and 1996. A mean of 138 lambs were
expected at ultrasounding from 100 ewes and 113 lambs per 100 ewes were alive at
lamb marking.
There was no significant (P>0.05) effect of fox control on lambing
performance (the number of lambs per 100 ewes that lambed) Fox predation was
inferred as the cause of lamb death in a minimum of 0.8% and a maximum of 5.3% of
lamb carcases during 1995 and 1996. There was a significant (P<0 05) effect of fox
control on the minimum possible percentage of lamb carcases classified as healthy
lambs killed by foxes, with the percentage declining from 1.50% (no fox control), to
0.90% (fox control once per year) to 0.25% (fox control three times per year). There
was also a significant (P<0.005) effect of fox control on the maximum possible
percentage of lamb carcases classified as healthy lambs killed by foxes with the
percentage declining from 10.25% (no fox control), to 6.50% (fox control once per
year) to 3.75% (fox control three times per year). The observed results were used to
estimate the number of treatment replicates needed to be confident of detecting an
effect of predator control on lamb marking performance. The estimated numbers
were very high if small effects were to be detected. No significant correlation
between the fox density and the minimum and maximum possible number of lambs
carcases classified as killed by foxes was found. Bait uptake was monitored as were
the costs of fox control.
| Identifer | oai:union.ndltd.org:ADTP/218970 |
| Date | January 2000 |
| Creators | Greentree, Carolyn, n/a |
| Publisher | University of Canberra. Science &Design |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Carolyn Greentree |
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