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Refining Operational Practice for Controlling Introduced European Rabbits on Agricultural Lands in New Zealand.

Latham AD, Latham MC, Nugent G, Smith J, Warburton B - PLoS ONE (2016)

Bottom Line: In each case, experimental sowing via strip patterns using 10-15 kg of bait per hectare was compared with the current best practice of aerial broadcast sowing at 30-35 kg/ha.We project that strip-sowing could reduce by two thirds the amount of active 1080 applied per hectare in aerial control operations against rabbits, both reducing the non-target poisoning risk and promoting cost savings to farming operations.These results indicate that, similarly to the recently-highlighted benefits of adopting strip-sowing for poison control of introduced brushtail possums (Trichosurus vulpecula) in New Zealand, aerial strip-sowing of toxic bait could also be considered a best practice method for rabbit control in pest control policy.

View Article: PubMed Central - PubMed

Affiliation: Wildlife Ecology & Management, Landcare Research, P.O. Box 69040, Lincoln 7640, New Zealand.

ABSTRACT
European rabbits (Oryctolagus cuniculus) pose a major threat to agricultural production and conservation values in several countries. In New Zealand, population control via poisoning is a frontline method for limiting rabbit damage, with large areas commonly treated using the metabolic toxin sodium fluoroacetate ('1080') delivered in bait via aerial dispersal. However, this method is expensive and the high application rates of the active ingredient cause public antipathy towards it. To guide reductions in cost and toxin usage, we evaluated the economics and efficacy of rabbit control using an experimental approach of sowing 1080-bait in strips instead of the commonly-used broadcast sowing method (i.e. complete coverage). Over a 4-year period we studied aerial delivery of 0.02% 1080 on diced carrot bait over ~3500 ha of rabbit-prone land in the North and South islands. In each case, experimental sowing via strip patterns using 10-15 kg of bait per hectare was compared with the current best practice of aerial broadcast sowing at 30-35 kg/ha. Operational kill rates exceeded 87% in all but one case and averaged 93-94% across a total of 19 treatment replicates under comparable conditions; there was no statistical difference in overall efficacy observed between the two sowing methods. We project that strip-sowing could reduce by two thirds the amount of active 1080 applied per hectare in aerial control operations against rabbits, both reducing the non-target poisoning risk and promoting cost savings to farming operations. These results indicate that, similarly to the recently-highlighted benefits of adopting strip-sowing for poison control of introduced brushtail possums (Trichosurus vulpecula) in New Zealand, aerial strip-sowing of toxic bait could also be considered a best practice method for rabbit control in pest control policy.

No MeSH data available.


Related in: MedlinePlus

Schematic diagram of two methods of aerially-sowing 1080-covered carrot baits to control rabbits within 100 ha experimental plots in semi-arid regions in New Zealand.Broadcast baiting (a) entails complete coverage of the area with carrot baits at a density of 0.5/m2. Using a fixed-wing aircraft, this pattern was achieved by deploying strips of baits every 25 m (i.e. the flight path spacing; FPS), with each delivery of bait having a swath width of 25 m (c). This treatment leaves no unbaited gaps. Strip-sowing (b) entails partial coverage of the area with carrot baits at a target density of 1.25/m2 within the baited strips. This was achieved by deploying strips of baits every 75 m (i.e. the FPS), with each strip having a target swath width of 10 m (d). This treatment leaves unbaited gaps of 65 m in width between the outer extremities of swaths of bait.
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pone.0158078.g002: Schematic diagram of two methods of aerially-sowing 1080-covered carrot baits to control rabbits within 100 ha experimental plots in semi-arid regions in New Zealand.Broadcast baiting (a) entails complete coverage of the area with carrot baits at a density of 0.5/m2. Using a fixed-wing aircraft, this pattern was achieved by deploying strips of baits every 25 m (i.e. the flight path spacing; FPS), with each delivery of bait having a swath width of 25 m (c). This treatment leaves no unbaited gaps. Strip-sowing (b) entails partial coverage of the area with carrot baits at a target density of 1.25/m2 within the baited strips. This was achieved by deploying strips of baits every 75 m (i.e. the FPS), with each strip having a target swath width of 10 m (d). This treatment leaves unbaited gaps of 65 m in width between the outer extremities of swaths of bait.

Mentions: To produce bait, a Reliance bait cutter fitted with a 29 mm grill [36] and a 19 mm drum screener were used to produce average 6 g dices of carrot. Toxin-loading was achieved by coating carrots with 1080 (aqueous form) to a final concentration of 0.02% wt/wt 1080:carrot [17]. Toxic bait was sown 5–7 days following the second pre-feed. In Central Otago, 1080-carrot bait was broadcast-sown at 30 kg/ha as per recommended best practice for rabbit populations at the modified McLean Scale of 5–6 (Table 1; [18]). For strip-sowing in the same area, 1080-carrot bait was applied at 10 kg/ha by using GPS-guidance to deploy bait in strips aiming to be 10 m-wide with a flight path spacing (FPS) of 75 m between the strips (Table 1, Fig 2). In Hawkes Bay, the same procedures were followed but with elevated sowing rates to 35 kg/ha and 15 kg/ha for broadcast- and strip-sowing, respectively, to account for the higher estimated rabbit densities. We used a fixed-wing aircraft (Walter turbine-powered Fletcher) to sow bait in 11 treatment blocks in Central Otago. Where there was no nearby airstrip or other restrictions applied, we instead used a Bell 206 helicopter fitted with either of two buckets, namely one with a conventional bait spinner for broadcasting [27] or one set up to trickle-feed bait for strip sowing in ~10 m swaths. Although the mechanisms by which baits were sown from a helicopter differed slightly, they achieved similar patterns of bait for broadcast and strip-sown treatments as a fixed-wing aircraft (Table 1): in total, 8 blocks in Central Otago were sown via helicopter and 3 in Hawkes Bay. Prior to trial commencement, practice-runs were performed over flat fields and the distribution pattern and size of bait deployed by each aircraft type was determined by hand-collecting baits from the ground.


Refining Operational Practice for Controlling Introduced European Rabbits on Agricultural Lands in New Zealand.

Latham AD, Latham MC, Nugent G, Smith J, Warburton B - PLoS ONE (2016)

Schematic diagram of two methods of aerially-sowing 1080-covered carrot baits to control rabbits within 100 ha experimental plots in semi-arid regions in New Zealand.Broadcast baiting (a) entails complete coverage of the area with carrot baits at a density of 0.5/m2. Using a fixed-wing aircraft, this pattern was achieved by deploying strips of baits every 25 m (i.e. the flight path spacing; FPS), with each delivery of bait having a swath width of 25 m (c). This treatment leaves no unbaited gaps. Strip-sowing (b) entails partial coverage of the area with carrot baits at a target density of 1.25/m2 within the baited strips. This was achieved by deploying strips of baits every 75 m (i.e. the FPS), with each strip having a target swath width of 10 m (d). This treatment leaves unbaited gaps of 65 m in width between the outer extremities of swaths of bait.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4920370&req=5

pone.0158078.g002: Schematic diagram of two methods of aerially-sowing 1080-covered carrot baits to control rabbits within 100 ha experimental plots in semi-arid regions in New Zealand.Broadcast baiting (a) entails complete coverage of the area with carrot baits at a density of 0.5/m2. Using a fixed-wing aircraft, this pattern was achieved by deploying strips of baits every 25 m (i.e. the flight path spacing; FPS), with each delivery of bait having a swath width of 25 m (c). This treatment leaves no unbaited gaps. Strip-sowing (b) entails partial coverage of the area with carrot baits at a target density of 1.25/m2 within the baited strips. This was achieved by deploying strips of baits every 75 m (i.e. the FPS), with each strip having a target swath width of 10 m (d). This treatment leaves unbaited gaps of 65 m in width between the outer extremities of swaths of bait.
Mentions: To produce bait, a Reliance bait cutter fitted with a 29 mm grill [36] and a 19 mm drum screener were used to produce average 6 g dices of carrot. Toxin-loading was achieved by coating carrots with 1080 (aqueous form) to a final concentration of 0.02% wt/wt 1080:carrot [17]. Toxic bait was sown 5–7 days following the second pre-feed. In Central Otago, 1080-carrot bait was broadcast-sown at 30 kg/ha as per recommended best practice for rabbit populations at the modified McLean Scale of 5–6 (Table 1; [18]). For strip-sowing in the same area, 1080-carrot bait was applied at 10 kg/ha by using GPS-guidance to deploy bait in strips aiming to be 10 m-wide with a flight path spacing (FPS) of 75 m between the strips (Table 1, Fig 2). In Hawkes Bay, the same procedures were followed but with elevated sowing rates to 35 kg/ha and 15 kg/ha for broadcast- and strip-sowing, respectively, to account for the higher estimated rabbit densities. We used a fixed-wing aircraft (Walter turbine-powered Fletcher) to sow bait in 11 treatment blocks in Central Otago. Where there was no nearby airstrip or other restrictions applied, we instead used a Bell 206 helicopter fitted with either of two buckets, namely one with a conventional bait spinner for broadcasting [27] or one set up to trickle-feed bait for strip sowing in ~10 m swaths. Although the mechanisms by which baits were sown from a helicopter differed slightly, they achieved similar patterns of bait for broadcast and strip-sown treatments as a fixed-wing aircraft (Table 1): in total, 8 blocks in Central Otago were sown via helicopter and 3 in Hawkes Bay. Prior to trial commencement, practice-runs were performed over flat fields and the distribution pattern and size of bait deployed by each aircraft type was determined by hand-collecting baits from the ground.

Bottom Line: In each case, experimental sowing via strip patterns using 10-15 kg of bait per hectare was compared with the current best practice of aerial broadcast sowing at 30-35 kg/ha.We project that strip-sowing could reduce by two thirds the amount of active 1080 applied per hectare in aerial control operations against rabbits, both reducing the non-target poisoning risk and promoting cost savings to farming operations.These results indicate that, similarly to the recently-highlighted benefits of adopting strip-sowing for poison control of introduced brushtail possums (Trichosurus vulpecula) in New Zealand, aerial strip-sowing of toxic bait could also be considered a best practice method for rabbit control in pest control policy.

View Article: PubMed Central - PubMed

Affiliation: Wildlife Ecology & Management, Landcare Research, P.O. Box 69040, Lincoln 7640, New Zealand.

ABSTRACT
European rabbits (Oryctolagus cuniculus) pose a major threat to agricultural production and conservation values in several countries. In New Zealand, population control via poisoning is a frontline method for limiting rabbit damage, with large areas commonly treated using the metabolic toxin sodium fluoroacetate ('1080') delivered in bait via aerial dispersal. However, this method is expensive and the high application rates of the active ingredient cause public antipathy towards it. To guide reductions in cost and toxin usage, we evaluated the economics and efficacy of rabbit control using an experimental approach of sowing 1080-bait in strips instead of the commonly-used broadcast sowing method (i.e. complete coverage). Over a 4-year period we studied aerial delivery of 0.02% 1080 on diced carrot bait over ~3500 ha of rabbit-prone land in the North and South islands. In each case, experimental sowing via strip patterns using 10-15 kg of bait per hectare was compared with the current best practice of aerial broadcast sowing at 30-35 kg/ha. Operational kill rates exceeded 87% in all but one case and averaged 93-94% across a total of 19 treatment replicates under comparable conditions; there was no statistical difference in overall efficacy observed between the two sowing methods. We project that strip-sowing could reduce by two thirds the amount of active 1080 applied per hectare in aerial control operations against rabbits, both reducing the non-target poisoning risk and promoting cost savings to farming operations. These results indicate that, similarly to the recently-highlighted benefits of adopting strip-sowing for poison control of introduced brushtail possums (Trichosurus vulpecula) in New Zealand, aerial strip-sowing of toxic bait could also be considered a best practice method for rabbit control in pest control policy.

No MeSH data available.


Related in: MedlinePlus