NZ330900A - Poison bait dispenser activated by weight of animal and with an abrupt reset facility - Google Patents

Abstract

Provided is an animal trap. The trap includes a dispensing means to dispense poison or other population control substances and a time delay rest means. The time delay rest means allows for the abrupt resetting of the dispensing reservoir. This means that both the correct dosage of poison will be dispensed allowing for "kill" and that wastage or overdispensing of poison is kept to a minimum.

Description

NEW ZEALAND PATENTS ACT, 1953 No: 330900 Date: 6 July 1998 COMPLETE SPECIFICATION POISON BAIT DISPENSER We, THE HORTICULTURE AND FOOD RESEARCH INSTITUTE OF NEW ZEALAND LIMITED, a New Zealand company of Batchelar Research Centre, Highway 57, Palmerston North, New Zealand, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: TECHNICAL FIELD This invention relates to any field that may use devices for controlling populations of animals, in particular pest animals such as possums. The background and the invention will be described primarily with reference to control of possum populations in New Zealand, but the principles may also be applied to other animal pests, for example rats, deer, foxes, stoats and cats.

BACKGROUND ART Limitations of current possum control methods Trapping is an environmentally benign way of reducing animal pest populations. It can be very effective, but conventional traps need to be reset manually. They also restrain the captured animal if they fail to kill it, and animal welfare considerations require that traps be inspected daily to prevent undue distress to trapped animals. Daily inspection and manual resetting make trapping too costly to be a practical control method over large areas of land.

Poisoning is a widely-used method of controlling animal pest populations, but poisoning often fails to provide adequate control because it relies on voluntary ingestion of a poisoned substance by the animal. It is difficult to formulate a substance that is successful for this purpose, because a high concentration of poison is likely to lead to detection and avoidance by the animal, and may lead to human safety problems; and a low concentration is likely to lead to the animal ingesting a sub-lethal dose, and thereafter avoiding similar baits because of the associated unpleasant experience. Aerial broadcast poisoning raises serious environmental and political concerns, and meets strong public opposition. Poisoning can also be a danger to non-target animals.

Bait stations are relatively benign because poison is localised, but there is a high cost due to the need for several visits per year. Aversion often arises due to sublethal dosing as already explained, and there can be high bait cost due to possums consuming many times more than a lethal dose of the more expensive baits. Current baits last only a few weeks or months due to the need for the baits to be edible. Deterioration of the baits can also lead to sublethal dosing and subsequently avoidance of similar baits because of the associated unpleasant experience.

It is considered that all current forms of poison delivery fail to provide adequate control of possums.

Deterioration of bait 330900 Conventional baits last only a month or two before they degrade, even in bait stations, so the possum population soon starts to increase again, and repeat operations as often as every year are required to achieve effective control.

The short life of conventional pellet baits is inherent in the fact that the pellets need to be recognised as desirable feed material by possums, and so they are necessarily made of materials that degrade in the humid conditions of the bush. Even if degradation could be slowed, it is likely that within a few months the pellet dispenser would be colonised and disabled by insects and algae.

Deterioration of baits could play a significant part in the build-up of learned aversion that causes serious problems for conventional possum control. Since conventional bait formulations are generally only marginally lethal with a single pellet, oxidation, hydrolysis, leaching or fragmentation of the pellets will increase the probability that the possum will receive only a sublethal dose and develop a lasting aversion.

Protection against fouling Any device intended for long-term use in the bush without maintenance must be carefully designed to resist fouling. This may take many forms: growth of algae, bacteria or lichen; accumulation of windblown dust; corrosion of moving parts; intrusion of growing plants; lodging of fallen branches or leaves; nesting by insects or rats; actions of animals; vandalism by humans. Desirably, a pest control device will avoid debris from entering when the device is activated which might then prevent the device from resetting.

Blockage Any device that involves release of a liquid will have to be resistant to blockage of the orifice by solidification of the liquid, which may remain undisturbed for many months once the initial high pest population has been reduced. Blockage might result from evaporation leading to crystallisation or formation of viscous plugs; polymerisation under ultraviolet light; growth of micro-organisms; or colonisation by ants.

Limiting the dispensed volume Unless a very rapid-acting poison is used, there will be serious wastage of poison bait due to overdosing of animals. Field observations have revealed that possums that are able to pump feed continuously will do so in most cases, often consuming 200 ml of sugar syrup in a continuous work effort lasting an hour or more.

INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 5 OCT 2000 Electro-mechanical timers are a ready technical solution, but are unlikely to be acceptable because of cost and reliability constraints. A lower-cost option is therefore required.

It is one object of the present invention to address the problems set out above while still aiming to meet the criteria for economics, protection against fouling and blockage, and limiting the dispensed volume and interval of delivery. An alternative object is to provide the public with a useful choice as to poison dispensing devices and methods of attracting or killing a target animal.

DISCLOSURE OF INVENTION In accordance with a first aspect of the present invention there is provided a device for population control of a target animal, the device including a dispensing means including dosage means to dispense a predetermined amount of a control substance and a time delay reset means to delay resetting of the dispensing means for a predetermined period of time, wherein the time delay reset means is operable such that, after the predetermined period of time, the reset occurs abruptly to minimise the chance of an amount less than the predetermined amount of the control substance being dispensed to a target animal.

Described herein is a device for population control of a target animal including: a first moveable platform portion and a second moveable platform portion; a dispensing means having triggering means which is normally actuable solely by the weight of a target animal on both platform portions, wherein the dispensing means is responsive to actuation of the triggering means to dispense a poisonous substance.

Preferably, a stop is also provided which limits the downward movement of one of the portions to ensure that both portions are not depressed in the event of weight being provided on only the one portion. The two platforms may be hingedly connected. Furthermore, the two platforms may be integrally constructed with a region of reduced thickness provided at the hinged connection.

INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 0 NOV 2000 received 330900 More specifically, the invention relates to a poison bait dispenser capable of long field life, comprising a dispenser for scent lure or liquid unpoisoned bait, a mechanism for dispensing poison only in the presence of an animal, a mechanism for making triggering by non-target animals very unlikely, a mechanism for delaying the reset of the dispenser to prevent overdosing of animals and wastage of bait, and a device for preventing inadvertent triggering by birds perching on the trigger. In some embodiments some of the above elements may not be present.

In one embodiment of the invention, the dispenser is a platform attached to a post. A lure attracts animals to the device. The platform is hinged close to the post, but prevented from dropping under the weight of an investigating animal by a trigger mechanism. Only when the animal has weight simultaneously on the platform and on the trigger will the platform drop. The dropping movement causes the release of a poisoned bait close to the animal's nose, providing a strong stimulus for the bait to be eaten. Excessive consumption of the bait by a single animal is prevented by a time delay latch that prevents resetting of the mechanism for a time sufficient to avoid a significant number of repeat triggerings by the same animal. Deterioration of the bait and the lure is minimised by holding both in reservoirs that prevent contact between the contents and air except at the point of discharge.

To prevent inadvertent poisoning of birds and humans, the main protection provided by a preferred embodiment is the two-stage triggering mechanism. Weight on the platform or pressure on the trigger separately do not cause the discharge of poison. Birds such as wood pigeons and keas cannot simultaneously activate both components of the trigger mechanism while landing, when their momentum gives them a greater effective weight. To guard against the danger that two heavy birds might activate the dispenser when one lands on the trigger while the other is perched on the platform, a guard bar can be provided that will discourage birds from landing on the trigger plate.

Humans will not be able to activate the dispensing device of the preferred embodiment, except by a deliberate two-handed action.

Also described herein is a poison dispensing device for population control of a target animal, the device including a poison dispensing means including dosage means to dispense a predetermined amount of poison and a time delay reset means to delay resetting of the poison dispensing means for a predetermined period of time.

Also described herein is a device for population control of a target animal including: dispensing means for dispensing poison intended for the target animal; and attractant dispensing means for dispensing a substance to attract the target animal INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 5 OCT 2000 n p P I u P n 330900 Preferably, the attractant dispensing means is adapted to continuously dispense the attractant substance. On the other hand, the poison dispensing means may dispense poison only periodically. For example, the poison dispensing means may be activated by the target animal.

The attractant dispensing means may be adapted to dispense a liquid or a gaseous substance. For example, the attractant dispensing means may dispense a scent which is attractive to the target animal Where the attractant substance is a liquid, preferably the attractant dispensing means is adapted to dispense a viscous liquid. In this regard, the attractant dispensing means may be provided with flow rate control means. In a preferred embodiment, the flow rate control means is governed by the flow rate of water through a flow restrictor eg. a porous plug. Optionally, where the attractant substance is a liquid, the attractant dispensing means may operate under gravity flow.

Also described herein is a method of attracting a target animal to a device for eradicating target animals, the method including dispensing attractant fluid from the device.

The attractant fluid may be dispensed in a liquid or gaseous form. For example, the gas may comprise a scent which is attractive to the noxious animals. Preferably, the attractant fluid is dispensed continuously. The dispensing of the attractant fluid may be achieved by gravity. Preferably, the dispensing is conducted at a slow rate. In a preferred form of the invention, the attractant liquid may include insect repellant.

Also described herein is a method of killing a target animal including: attracting the target animal as outlined above; dispensing poison as well as dispensing a non-poisonous substance over the poison to mask the smell of the poison.

Also described herein is a method of poisoning a target animal by providing a device having poison dispensing means with a triggering means which is actuable by a target animal and dispensing poison from the poison dispensing means on actuation of the triggering means by the target animal.

INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 5 OCT 2000 rftfived 330900 Preferably the triggering means is actuable by the weight of the animal. Desirably, the poison is dispensed in discrete doses sufficient to kill the target animal. A predetermined time delay might be provided between subsequent doses.

The method might further include the step of dispensing an attractant substance to lure the animal. Preferably the target animal is a possum BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present invention will now become apparent from the ensuing description which is given by way of example only and with reference to the accompanying drawings in which: INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 5 OCT 2000 RECEIVED Figure 1 shows side and top diagrammatic views of a preferred embodiment of the present invention, in which a piston pump is used to dispense liquid bait, and Figure 2 shows side and top diagrammatic views of a preferred embodiment of the present invention, in which peristaltic compression of a plastic sachet is used to do the pumping, and Figure 3 shows side and top diagrammatic views of a preferred embodiment of the present invention, in which poison is dispensed from a metered-dose aerosol-type dispenser. The latching components are omitted from the top view for clarity. Figure 3 also shows a guard bar that diminishes the likelihood that birds will activate the dispenser.

Figure 4 shows a side view of a latch mechanism suitable for introducing a reset delay of the order of twenty minutes, and Figure 5 shows a mechanism for slow dispensing of a syrup such that variation in flow due to temperature variations is very small.

Figure 6 shows an alternative mechanism for triggering the device, with most other components omitted for clarity.

BEST MODES FOR CARRYING OUT THE INVENTION The ensuing description is given by way of example only.

In Fig 1, a platform 1 which is about 400 mm long by 120 mm wide has flexible hinges at points 2 and 3. A sturdy bracket 4 allows the device to be fixed to a tree with nails. The bracket will be adjustable to accommodate a range of trunk angles, and will be removable for compact stacking during transport. A bottom platform 5 is rigidly attached to the bracket. The bottom platform holds poison sachet 6 and attractant sachet 7, which are made of flexible plastic impermeable to atmospheric oxygen and moisture. The attractant sachet is lightly pressurised with a leaf spring (not shown) and discharges continuously to the air at a very low rate.

The top platform 1 is held up by the support column 8. This is preferably a close-wound coil spring, loosely attached at the ends to moulded pins 9 that are integral with the top and bottom platforms.

When an animal approaches the device and puts some weight on the top platform, the support column provides rigid support and the top platform will feel stable to the animal, encouraging it to commit itself to the platform in order to investigate the source of attractant odour at release point 10, and/or a visual lure suspended from the end of the top platform (not shown).

When the animal approaches the end of the platform and puts weight on the trigger plate 11, the middle of the support column is pushed sideways by the push bar 12 and buckles, allowing an abrupt collapse of the top platform under the weight of the animal. The weight is substantially greater than is necessary to fully depress the piston of the pump 13, which ejects approximately 2 ml of liquid onto the top platform. The liquid is in a semi-gelled form so that it will lie on the platform in a compact blob and be easily consumed completely by the animal.

While the animal remains on the platform no further liquid will be pumped. When the animal leaves the platform, a spring 15 lifts the top platform to its original position. In preferred embodiments a reset delay latch 16 ensures that the platform does not return to the reset position for perhaps 20 minutes. Otherwise the animal might return immediately and dispense itself a wasteful quantity of bait.

Freedom from fouling points The external parts of the device include no pinch points which can be fouled by debris, and no pivots or bearings that can become corroded or jammed. Hinges 2 and 3 may be provided by a rubber top layer or by flexible-plastic sections of the platform moulding, or they may protected by flexible seals.

The entire mechanism of the device is enclosed in a protective container 17, which has no apertures to allow the entry of insects that might colonise the interior. The flexible inserts 18 and 19 accommodate the movement of the internal parts without significant resistance.

The buckling spring support column was chosen over other ways of achieving the sudden drop of the top platform, because by this means the entire device is free of pivots, bearings, or precision components susceptible to fouling or corrosion.

Protection of birds and humans In normal operation the trigger plate 11 causes the support column 8 to start buckling, but the weight of the animal on the top platform is what causes the subsequent collapse of the support column. This provides a built-in protection against species other than possums.

If a bird lands on the top platform without pressing on the trigger plate, the platform support will remain rigid and nothing will happen. If a bird lands on the trigger plate, it might do so with sufficient impact to depress the trigger and displace the support column. However, with less than about 1 kg on the platform the column will not buckle.

An animal whose weight is insufficient to fully depress platform 1 is unlikely to be able to overcome the force required to move the trigger plate.

With continued heavy pressure on the trigger plate 11, it would be possible to drag down the whole platform 1 and dispense bait, if it were not for the stop defined by the engagement between a projection on the push bar 12 and an upright 20. This prevents further movement of the trigger plate 11 just after it has travelled sufficiently to buckle the support column 8. The support column 8 does not collapse, because there is no weight on the platform 1, and the stop prevents the downward force on the trigger plate 11 being transmitted to the platform 1.

In an alternative embodiment, illustrated in Fig 6, an equivalent function is provided by different means. In this illustration the support column 70 is displaced by push bar 71 when the trigger plate 72 is depressed and moves arm 77 about pivot point 78. Flexible seal 79 prevents ingress of dust, moisture and insects. If there is insufficient weight on the platform 73, the push bar 71 comes to rest on the plane 74 of stop 75. The angle of this plane 74 is chosen such that pressure on trigger plate 72 will not result in the push bar 71 sliding down the face of the stop 75, and platform 73 will not move significantly downward. However, if there is sufficient weight on platform 73, the column 70 will collapse further when it is buckled by pressure from push bar 71, and the push bar 71 will strike the stop 75 on plane 76. The angle of this plane 76 is chosen such that the push bar 71 will slide down it, allowing the collapse of platform 73".

These trigger mechanisms also prevent careless discharge by humans, who could thereby endanger birds (which would then have access to the poison) or themselves. A human can still cause a discharge, but only by using two hands on the device, which will normally be above head height.

Slow dispensers for attractant Dispensing a chemical or food attractant over a period of years can be achieved by providing a slow but continuous flow of a liquid foodstuff (e.g. a sugar syrup) through a small orifice, or by volatilisation of an attractant chemical.

An advantage of a high-viscosity liquid bait (which will be referred to as a syrup, but which may be some other liquid) is that it can form a bulky trail down a tree, and the trail will tend to lead a possum from the ground up to a poison dispenser. This would gain the attention of the possum on the ground, where they appear to locate objects more readily than in trees, but still provide the safety and species discrimination of a tree mounted dispenser. The syrup trail should also act like a prefeed in getting the animal accustomed to (and enthusiastic about) the taste of that syrup before being presented with the same syrup containing a poison. A thin fluid is likely to be absorbed by the tree and provide a less satisfying experience for the animal.

A problem with dispensing a high viscosity syrup is to find a system that will maintain an acceptable dispensing rate in the face of the large viscosity change exhibited by most syrups over the necessary temperature range (up to 10:1 over the range 5-25C). Such a viscosity change makes simple gravity or pressurised flow through a restriction (e.g. a very small orifice) unsuitable in many circumstances, because an orifice which gives adequate flow in winter will give excessive flow in summer and cause premature exhaustion of the bait. In one embodiment of the invention we have added a thickening agent to the syrup, resulting in almost no significant variation in syrup viscosity over this temperature range.

In another embodiment, the effect of viscosity variation on bait flow is made insignificant by using a second fluid with negligible viscosity variation, for example water, to displace the syrup from its container. The restriction that limits the flow of syrup is then not the orifice through which the syrup flows, but the restrictor through which the second fluid flows. In a preferred embodiment purified water under gravity or light spring pressure permeates through a porous plug, for example made of ceramic. The flow rate is virtually constant because water viscosity only changes slightly over the likely environmental temperature range. The disadvantage of such a water displacement mechanism is that the weight of water to be carried roughly equals that of the bait.

Because the syrup flows continuously from the dispenser, if the orifice is small diameter (typically less than 1 mm) the speed of flow through the orifice will be sufficient to prevent entry of micro-organisms or blockage of the orifice through crystallisation of the syrup.

Since the syrup trail is unpoisoned it is not directly a threat to non-target organisms. However, bees, wasps and ants are likely to be significant in removing the trail, and compounds such as isovaleric acid have been identified as candidate insect repellents.

The inventions described in this application, provide a means of dispensing 0.5 ml per day at a substantially constant rate without limitation to reservoir volume.

Scents that do not contain sugar or food are relatively easily dispensed from a reservoir of liquid, using pressure-driven diffusion of liquid through a porous plug to determine the rate of release. Using the liquid flow as the limiting factor is better than using wick or impregnated-matrix systems, because in these the rate of release is determined by the rate of evaporation, which is of course much higher at high temperatures, and the bulk of the scent would be wasted by release during the day when possums are not active.

Pump mechanism In Fig 1 the pump is a standard piston pump. It is very cheap yet reliable, has a suitable discharge volume, and is designed for the semi-gelled liquids of similar viscosity to the formulations preferred as poison bait.

The weakest part of a low-cost piston pump is the integrity of the non-return valves. However, possible leaky valves are not of concern in this design. The poison-bait container 6 is placed above the bottom of the piston, so that the liquid cannot drain back and cause a partial dose to be discharged at the next triggering. The poison-bait container is also placed below the discharge point on the top platform, so that poison will not leak out.

Blockage prevention To allow a five year life, prevention of blockage at the discharge point is critical. The invention may include one or more methods of preventing blockage: Keeping the part of the discharge tube 21 that is exposed to air as short as possible, so that pressure generated during discharge has a better chance of clearing any blockage that might form.

• Making the discharge tube 21 very flexible, so that it can deform under pressure to dislodge a blockage.

Combining both of these factors by squeezing the end of a flexible discharge tube 21 shut with a light flat spring, close to the tip.

Using an aerosol-type pressure can to provide the discharge, thereby taking advantage of the self-clearing properties of aerosol designs.

Incorporating anti-microbial substances in the liquid to prevent bacterial and fungal growth. Considering that the bait is poisoned, these can be allowed to be quite toxic, so there is a wide variety to choose from.

Instead of a sugar-based syrup, using a bait that is not subject to solidification. This may be done by using an effectively non-solidifying liquid such as propylene glycol or an oil. A low-solids (for example 3% dry matter) bait based on artificial thickeners, sweeteners or appetite enhancers may solidify but would form a very fragile blockage that would be easily dislodged.

Peristaltic version In the embodiment shown in Fig 2, the pump 13 of Fig 1 is replaced by a peristaltic system, which has potential to allow the whole unit to be made more compact and lower in cost.

When platform 1 drops, the spongy pad 30 first closes off a section of the poison sachet 31. Further movement of pad 30 squeezes out a volume of perhaps 2 ml of fluid through orifice 32. This orifice is simply the lips of the extension of sachet 31, which are normally held pressed together by the light leaf spring 33.

When the platform resets, orifice 32 acts as a one-way valve, and the emptied section of the sachet refills from the larger part of the sachet.

Scent is delivered from sachet 34.

Pressure-can version In the embodiment shown in Fig 3, the pump 13 of Fig 1 is replaced by a pressurised can 39 of the "aerosol" type, preferably one which incorporates a mechanism for delivering a viscous liquid with a limited discharge volume (preferably in the range 0.5 to 3 ml) on each depression of the discharge valve. These are commercially available.

When platform 1 drops, the compression of the discharge valve 40 causes the contents of the metering compartment within the can 39 to be delivered through tube 41. The reset delay latch 16 prevents the platform 1 from lifting, which in turn prevents valve 40 from returning to its normal closed position until latch 16 releases. While valve 40 is thus held open, the metering compartment within the can is not recharged with liquid bait. Recharging of this compartment occurs within a few seconds when the latch 16 releases and valve 40 closes. By this means release of poison in a quantum that is less than a lethal dose is made extremely unlikely.

Guard bar In Fig 3 there is shown a guard bar 42 which may in some embodiments be placed beside and above the trigger plate 11, and is attached to the top platform 1. Birds landing on the device will prefer to perch on the guard bar rather than on the trigger plate, and this largely eliminates the risk that two birds between them can trigger the mechanism. A baffle plate 43 may be provided to encourage possums or other target animals to put weight on the trigger plate in order to more closely investigate the source of the attractant odour, which is discharged underneath the baffle plate at release point 10. The attractant odour is delivered from sachet 44 through tube 45, which will preferably run through the inside of guard bar 42, which may be a hollow tube.

Enrobing of the poison In some embodiments the single poison container (6 in Figs 1 and 2, 39 in Fig 3) is replaced by dual containers. One contains poisoned bait, and the other contains unpoisoned bait. The discharge orifices of the containers are arranged such that on triggering of the invention liquid is discharged from both containers such that the unpoisoned liquid will flow over and cover the poisoned liquid, thus providing an enrobing effect which will prevent the animal from detecting the odour of the poison.

Reset delay latch The introduction of a 30-minute delay between leaving the platform and resetting the pump almost completely defeats repeat feeding.

To prevent a possum from gaining excessive bait by leaving the dispenser then immediately returning, which appears to occur too often to be tolerated, it will be necessary to delay the reset of the device by probably 20 minutes or more. The reset has to be abrupt, because a slow return to a fully reset position carries a risk that a second possum will approach the device while the poison dispenser reservoir is only partially replenished, and thereby receive a sub-lethal dose. This risk is high since possums are commonly seen waiting in the vicinity of a feeding possum, and move in to the feeder as soon as the first possum has moved on.

A mechanism which performs the function required of the reset delay latch 16 is shown in Fig 4. A suction cup 50 that is preferably made of a rubber-like resilient material is able to move within a cylinder 51. The cylinder contains a fluid 52. The device will work with air as the working fluid, but an oil is preferred because it allows the use of less precise manufacturing techniques for the components.

Shaft 53 is attached to platform 1 (shown in Figs 1-3), and the cylinder 51 is attached to bottom platform 5 (shown in Figs 1-3). When platform 1 drops, fluid is displaced around the edges of cup 50, and the cup is compressed against the bottom of cylinder 51. In preferred embodiments the clearance between cup 50 and cylinder 51 is generous so that platform can fall rapidly, but in some circumstances the clearance may be made small so that the fall of platform is substantially slowed by the fluid.

When the animal leaves platform 1, the suction between cup 50 and the cylinder 51 prevents platform 1 from rising more than a few millimetres, which is insufficient to allow any recharging of the poison delivery system in any of the versions shown in Figs 1-3.

However, fluid is allowed to leak into the gap between cup and cylinder through a small orifice such as the hole 54. This orifice may take other forms, for example it may be a groove in the bottom of cylinder 51. After a period which in the preferred embodiment is about 20 minutes, sufficient fluid will flow through the orifice to allow cup 50 to detach from cylinder 51. Fluid rapidly flows under the edges of the cup and shaft 53 and hence platform 1 can rise abruptly. The latch mechanism is then in its reset position.

Fluid spillage is prevented by means of flexible boot 55.

Attractant dispenser With reference to Fig 5, a liquid 60 (for example, a viscous syrup) is dispensed from a flexible and substantially gas-impermeable container 61 through an orifice 62. The rate of outflow of liquid 60 is determined by the expansion of flexible container 63, due to an ingress of liquid 64 (for example water) from flexible container 65. Containers 61 and 63 are constrained by a rigid structure as exemplified by rigid plates 66, so that expansion of container 63 forces a diminution in volume of container 61.

Liquid 64 is forced from container 65 by a source of substantially constant pressure, for example springs 67 acting on moveable plate 69, but which might also be the force of gravity or a gas-charged device similar to an aerosol can. The rate of egress of Uquid 64 is determined by the flow restrictor 68. This may be a porous plug (for example made of ceramic material), a porous or semi-permeable membrane, or a fine tube or orifice. Although the rate of flow will be influenced by the viscosity of liquid 64, the liquid can be selected such that the viscosity variation over the temperature range required for the device's operation (typically 5-25°C) will be insignificant to the proper functioning of the device.

Orifice 62 is of large enough diameter that it does not significantly limit the rate of flow of liquid 60, but small enough that the outward flow of liquid prevents any inward migration of microorganisms or crystallisation interfaces that might block the orifice or cause the liquid 60 to deteriorate.

In another embodiment of the invention, the attractant is a volatile liquid with little viscosity variation due to temperature changes in the expected range. In this case the dispenser may consist simply of the volatile liquid in container 65, pressure source 67 and flow restrictor 68.

In yet another embodiment of the invention, an attractant is provided that has a long attractive range, so that the number of poison dispensers per unit area can be lower, and the acceptable cost of each dispenser is higher. Under these circumstances an electronic timer and flow-control element may be used to allow emission of the attractant only at times of maximum effectiveness, for example at dusk or in autumn.

The advantages which are realised by one or more of the preferred embodiments set out above are as follows: A life of several years in the field without attention, thus reducing the high labour costs of maintaining bait stations and conventional traps Small size and weight to make back-packing to remote areas practical Virtually certain lethality, thus avoiding generation of learned bait-shyness High efficiency of use of expensive poisons, through reduced over-consumption Poisons to be inaccessible to birds, dogs and children Effective pest control at low population density.

Claims (25)

WHAT WE CLAIM IS: -17-

1. A device for population control of a target animal, the device including a dispensing means including dosage means to dispense a predetermined amount of a control substance and a time delay reset means to delay resetting of the dispensing means for a predetermined period of time, wherein the time delay reset means is operable such that, after the predetermined period of time, the reset occurs abruptly to minimise the chance of an amount less than the predetermined amount of the control substance being dispensed to a target animal.

2. The device as claimed in claim 1 wherein the time delay reset means includes a container having a working fluid therein, and a suction cup movably located in the working fluid, wherein the suction cup is attachable by suction to a first inner surface of the container, and wherein an orifice is provided which enables working fluid to enter between the suction cup and the first inner surface.

3. The device as claimed in claim 2 wherein the container defines a second inner surface or surfaces past which the suction cup moves in its reset action, with generous clearance being provided between the suction cup and the second inner surface(s).

4. The device as claimed in claim 2 or 3 wherein the orifice comprises a hole in the suction cup.

5. The device as claimed in claim 2 or 3 wherein the orifice comprises a groove in the first inner surface.

6. The device as claimed in any one of claims 2-5 wherein the working fluid is air.

7. The device as claimed in any one of claims 2-5 wherein the working fluid is oil.

8. The device as claimed in any one of the preceding claims, further including: a triggering means to trigger the dispensing means, the triggering mpans inr.lnriing; INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 0 NOV 2000 RECEIVED 330900 a first moveable platform portion and a second moveable platform portion; wherein the triggering means is only operable by the weight of a target animal on both platform portions, with the first platform portion being mechanically linked to the dispensing means such that once the dispensing means is triggered, the weight of the target animal on the first platform portion causes dispensing of the population control substance.

9. The device as claimed in claim 8 wherein the first platform portion is supported by a support column which is capable of buckling under an axial load applied thereto as a consequence of weight on the first platform portion and a side load applied thereto as a consequence of weight on the second platform portion.

10. The device as claimed in claim 9 wherein the support column comprises a coil spring.

11. The device as claimed in any one of claims 8-10 wherein a stop is further provided to limit movement of the second portion beyond a predetermined point in the absence of weight on the first portion.

12. The device as claimed in any one of claims 8-11 wherein the two platform portions are hingedly connected.

13. The device as claimed in claim 12 wherein the two platform portions are integrally constructed from plastics material with a region of reduced thickness providing the hinged connection.

14. The device as claimed in any one of the preceding claims wherein the dispensing means comprises a piston pump.

15. The device as claimed in any one of claims 1-13 wherein the dispensing means comprises an aerosol container. INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 5 OCT 2000 RECEIVED 3309 -19-

16. The device as claimed in any one of claims 1-13 wherein the dispensing means comprises a peristaltic pump.

17. The device as claimed in any one of claims 14-16 including a further dispensing means for dispensing unpoisoned bait, wherein the population control substance dispensing means and the further dispensing means are operable to dispense the unpoisoned bait over the population control substance.

18. The device as claimed in any one of the preceding claims further including lure means to attract the target animal.

19. The device as claimed in claim 18 wherein the lure means is in the form of an attractant dispensing means to dispense an attractant substance.

20. The device as claimed in claim 19 wherein the attractant dispensing means is adapted to continuously dispense the attractant substance.

21. The device as claimed in claim 20 wherein the attractant dispensing means is provided with flow rate control means.

22. The device as claimed in claim 21 wherein the flow rate control means is governed by the flow rate of water through a flow restrictor.

23. The device as claimed in any one of claims 8-22 wherein a guard bar extends over the second platform portion.

24. The device as claimed in claim 23 when dependent on any one of claims 19-22 wherein the attractant dispensing means is operable to dispense attractant to a delivery site between the guard bar and the second platform portion. INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 5 OCT 2000 RECEIVED 3 J 0900

25. The device substantially as hereinbefore described with reference to the accompanying figures. By the authorised agents A. J. PARK f Pef(^\vdW^-- INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 5 OCT 2000 received