Poisons
Sodium monofluoroacetate (1080)
The report of the Feral Animal Search Conference (2) concluded that there wasn't enough evidence to decide whether 1080 was humane or not. However, descriptions of how animals die make it hard to believe they are not suffering. For example, here is how rabbits die (3):
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All affected rabbits exhibited increased sensitivity to noise or disturbance. Thereafter some recovered while the remainder experienced one or more convulsions, during which they coughed and squeaked, kicked with their hind legs and struggled for breath. Most convulsing rabbits eventually died, but a few recovered
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It is hard to believe that these rabbits were not suffering as they convulsed and struggled for breath. It took them between 3 and 44 hours to die after poisoning. Baits laced with 1080 can of course also be eaten by native animals; it has been estimated that baits laid for rabbits threaten 50 - 62 species, baits for dingoes 2 species, and baits for pigs 14 species (1).The kangaroo species, especially small ones, brush-tail possums and wombats are most at risk (1). This is a description of the death of Bennett's wallabies (3). Again it is hard to believe they were not suffering.
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Affected Bennett's wallabies were sometimes observed sitting hunched up, with heads held shakily just above the ground. Generally they appeared non-alert and 'sick', with shivering or shaking forelimbs and unsteady balance. Most individuals then eventually experienced convulsions, falling to the ground and lying on their backs and sides, kicking and making running motions with their hind legs before dying. Many individuals also ejaculated shortly before death, and, with others, exuded a white froth from their nostrils and mouth
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Not all species were affected in the same way; red-bellied pademelons did not convulse or froth, but both species died of gradual heart failure.
In carnivores such as dingoes, foxes, cats, as well as native carnivores, the central nervous system is involved. They become very agitated, tremble, convulse and vomit. The list of symptoms includes (4):
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...restlessness; increasing hyperexcitability or response to stimuli; bouts of trembling; rapid, shallow breathing; incontinence or diarrhoea; excessive salivation; twitching of the facial muscles; nystagmus (involuntary eyeball movement exposing the whites) or bulging eyes with large (dilated) pupils and rapid blinking (plus, in domestic cats, discharge of mucus from the eyes); slight lack of coordination or balance; abrupt bouts of vocalization; and finally, sudden bursts of violent activity such as racing around the cage, or biting the cage mesh or other objects.
All affected animals then fall to the ground in a tetanic seizure, with hind limbs or all four limbs and sometimes the tail extended rigidly from their arched bodies. At other times the front feet are clasped together, clenched or used to scratch frantically at the cage walls. This tonic phase is then followed by a clonic phase in which the animals lie and kick or 'paddle' with the front legs and sometimes squeal, crawl around and bite at objects. During this phase the tongue and penis may be extruded, they eyes rolled back so that only the whites show and the teeth ground together. Breathing is rapid but laboured, with some animals partly choking on their saliva. Finally such individuals begin to relax, breathing more slowly and shallowly and lying quietly with the hind legs still extended but apparently semiparalysed (paresis)
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The cats took 20-21 hours to die, the dingoes 5-10 hours. Apart from baits, carnivores can also be poisoned by eating prey containing 1080, for example, poisoned rabbits or wallabies.
From the descriptions given, 1080 does not seem to be a humane way to kill animals. With all poisons there is also the danger of killing animals other than those intended, as a CSIRO journal points out (5):
In the process of fumigation, poisonous gas is released into rabbit warrens. The report of the Feral Animal Search Conference (2) mentions 2 gases, namely phosphine and chloropicrin (tear gas). The report concludes that tear gas is not humane, but did not have enough evidence to make a decision about phosphine. The report said: "
Death from fumigation is not instantaneous and there is little or no data on the degree of suffering associated with it
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Phosphine (aluminium phosphide) is recommended by the SA Department of Agriculture in its fact sheet "Rabbit control" (Agdex 671). Pellets of aluminium phosphide are placed into warren entrances. They give off the poisonous gas phosphine when they get wet. The rabbits die underground, so no-one witnesses their degree of suffering. However, humans accidentally poisoned with aluminium phosphide had gastric pain and vomiting, followed by mental confusion and difficulty in breathing, and eventually heart failure (6). If the effect in rabbits is similar, this doesn't sound like a humane death!
During the 1992 mouse plague in South Australia, strychnine was used. This poison is also used against foxes and on traps set for dingoes. It is very cruel, and the Feral Animal Search Conference clearly considered it inhumane (2). It produces violent convulsions and painful muscle spasms. The Feral Animal Search Conference recommended that its sale and use be banned (2).
Victoria and South Australia now intend to use zinc phosphide (ZP) to kill mice in grain growing areas. The mice take up to 3 days to die, with the following symptoms (7):
Dogs who accidentally ate zinc phosphide showed symptoms including vomiting, aimless running and howling, and convulsions (8). It is certainly not a humane poison.
CSSP and warfarin are used to kill pigs. CSSP is 4% yellow phosphorus dissolved in carbon disulphide in molasses. It is popular in NSW and Queensland because it is cheap and readily available through stock and station agents. It is a powerful irritant that destroys the pig's gut and liver. Pigs take 2-4 days to die, so this is clearly not a humane poison. It can also kill animals who eat the carcase of poisoned pigs.
Warfarin is an anticoagulant. In humans excessive doses cause bleeding of internal tissues and organs. Pigs take 5-9 days to die. After 3 days they become lame, depressed and lethargic (9).
Poisons are a cruel way to kill animals. They also kill animals other than those intended, both directly through those animals eating baits, or indirectly by those animals eating the corpses of poison victims.
Feral animals in Australia: introduction
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Spreading vegetable baits laced with 1080 poison will always be of limited utility, since there is a constant danger that non-target species (especially those native animals already under pressure from competition by rabbits) will be destroyed
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Fumigation
Other poisons
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Damage caused by ZP poisoning includes central nervous system depression, irritation of the lungs, and damage to the liver and other organs. Symptoms include vomiting, diarrhoea, restlessness and fever, nausea, shock, weak heartbeat, low blood pressure, and loss of consciousness. Death may occur as a result of heart failure and pulmonary oedema
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Trapping
Introduced diseases
Mustering for slaughter and export
Other methods (shooting, warren ripping, dogging)
Alternatives to killing
References