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Alternatives to killing

The killing methods used on feral animals involve suffering, often to all affected animals, as with traps and poisons, or else to at least some of them, as with shooting. Many methods affect species other than those being targeted. Killing methods leave the breeding capacity of survivors unaffected, so unless killing is carried out year after year, the population will regenerate.

There are two basic humane approaches to animals causing problems:

• prevent them causing damage through deterrents and barriers;
• control their breeding to reduce the population.

Deterrents and barriers

Fencing

Animals can be kept out of areas where they can cause damage through appropriate fencing. For example, in South Australia strands of electrified wire have been placed alongside the netting dog fence, which is intended to keep dingoes out of sheep grazing areas. Not only is it successfully keeping dingoes on the right side of the fence, it is also preventing damage to the fence by wombats and kangaroos which then allows dingoes to get through (1). In Victoria a grazier has incorporated electrified wire within his existing fences and almost eliminated kangaroo and dingo/dog intrusions into his paddocks (2).

Sprays

If animals are causing damage to grass areas, such as golfing or bowling greens, there are non-toxic, biodegradable sprays that make the grass very unpleasant to eat. Animals will quickly leave and feed elsewhere. For an example of such a spray see ReJeX-iT.

To protect tree seedlings from rabbits and wallabies, the Victorian Institute of Animal Science has developed two non-toxic sprays (3).

WR-1 is sprayed onto the seedlings and a hard grit is then sprinkled over them. Rabbits and wallabies who try to eat the seedlings will find it very uncomfortable to chew grit, and will learn not to eat treated plants. The protection lasts for 10 months, enough time for the seedlings to become established.

AD-3 is a paste applied to the stakes next to seedlings. It very effectively repels rabbits for at least 10 months.

Scare devices

Scare guns and artificial hawks have been used for a long time to frighten animals, especially birds, away from crops. The problem is that the animals become accustomed to them and they lose their effect.

An Australian designed product is more effective at keeping birds and flying foxes away from orchards and vineyards in particular. Here's how it works:

• The approach of animals is detected by radar. Unlike scare guns, the alarm in the system only goes off when birds enter the area.
• When the alarm is triggered, it plays pre-recorded distress and alarm calls of the species that is causing problems. Social animals are frightened off when they hear such calls from one of their species - it signals danger.
• Each time the alarm goes off, the sequence of calls is changed so that animals don't keep hearing the same call. This makes sure the animals don't become accustomed to the same call.

Animals learn not to approach an area that is protected in this way, and crop damage is negligible. For more information see BirdDeter .

Fertility control

Methods of killing animals are not only cruel, they are also ineffective. Myxomatosis was a very lethal virus when first released and it decimated the rabbit population. However the survivors still managed to breed up to a population of 300 million by 1995. Donkey shooting in WA reduced the population by 83,000 but because it did not continue year after year, the population returned to where it was before shooting started. The best and most humane long-term option to reduce populations is fertility control to stop breeding.

Desex and return

There are many colonies of unowned cats around human settlements. Cats are very prolific breeders and these populations can expand to the point where the animals are unhealthy and a nuisance. People in the area can be disturbed by the fighting, spraying and caterwauling of the undesexed colonies. Authorities then try to eradicate the cats, sometimes by cruel methods. However, it is very unlikely that every single cat will be removed, and it only takes one breeding pair to re-establish the population. In addition, when an area is vacant, other cats will move in to claim the territory. The killing has to start all over again, ad nauseam.

Sarah Hartwell, of the Feline Advisory Bureau, gives a good example of how killing is not effective from Marion Island, a small island off South Africa:

" In 1949 , a group of scientists left the island, leaving behind 5 unneutered cats. By 1975 there were 2,500 cats on the island preying on ground-nesting seabirds. Deliberate infection with feline enteritis killed around 65% of the cats. Between 1986 and 1989 further surviving cats were exterminated by hunting. Finally poison was used to eliminate the remaining cats. It took 16 years of crude and cruel methods to eradicate 2,500 cats in a small, isolated area so how can eradication work where cats from outside can recolonise cleared areas? "

You can read the rest of Sarah's article "Why Feral Eradication Won't Work" .

A more humane and effective approach is to cage-trap cats, desex them, and return all healthy animals to the colony. A few caring residents ensure that they are well fed. The neutered cats are much healthier and in better condition without the stress of fighting and pregnancy. The problems of fighting, spraying, caterwauling and overpopulation are gone. The desexed cats defend a territory and keep out undesexed intruders.

For example, sister Sheila Young kept 3 desexed cats at Middlesex Hospital for 9 years. When a new administrator insisted they be removed, undesexed cats moved into the territory, and within 18 months there were 60 cats in the hospital grounds (4).

In Adelaide (SA) the organisation C.A.T.S. has desexed and returned many cat colonies. There are an increasing number of local councils that give C.A.T.S. annual grants for this purpose because they realise that cat problems are more effectively solved by this method than by killing (4).

In one well-known colony, cats were living in the rocks at West Beach. While not desexed, their numbers increased to 50. Since they were desexed 7 years ago, their number has fallen to 12 by natural attrition. They have kept undesexed cats out of the area (4).

For more information on this approach and examples of its success, see "A Report of Trap/Alter/Release Programs".

There are also suggestions on implementing the method:
Progressive Animal Welfare Society
Doris Day Animal League

Immuno-contraception

Australian scientists are leading the way in using an animal's own immune system to make it infertile. The immune system, in particular the B-lymphocyte blood cells, produce antibodies against any foreign protein to neutralise it. This is why we produce antibodies against viruses and bacteria, and also why foreign organs and blood are rejected when transplanted. Immuno-contraception involves tricking the body into thinking that some of the proteins in the outer coating of the egg or sperm are foreign. The body then mounts an antibody attack against these proteins. If the response is strong enough, fertilisation is prevented and no pregnancy will result.

First of all, scientists have to identify proteins:

• that are involved in the egg and sperm being able to attach to each other during fertilisation;
• that are specific to a particular species;
• that produce a strong antibody response.

The next step is to identify the DNA that codes for these proteins. For every protein produced by the body there is part of the DNA that contains the "recipe".

Finally, the relevant section of DNA is inserted into a virus or bacterium. When a animal is infected it will mount an antibody attack against the micro-organism's proteins which, because of the genetic engineering, include sperm or egg proteins as well.

Immuno-contraception, unlike hormonal contraception and surgical castration/spaying, is not supposed to alter the behaviour of the animals. They should mate normally and maintain their normal social structure. This is because in rabbit and fox groups, the dominant females suppress breeding in subordinate females. If dominant females were sterilised and couldn't defend their top position, then other females could take over the breeding and benefits would be lost. To be effective, the social structure has to remain the same after animals become infertile.

Rabbits

The idea of immuno-contraception was first applied to rabbits because of their phenomenal breeding capacity. Female rabbits (called does) can become pregnant when they are only 3 to 4 months old (5). Each pregnancy lasts only 30 days, after which the doe quickly comes into season again. There are usually 4 to 5 young in each litter. A doe produces between 1 and 5 litters a year, depending on environmental conditions, but she can produce a maximum of 8 litters a year. What this means is that an average breeding doe produces around 11 young a year in marginal habitats and around 25 young a year when conditions are more favourable (5). Of course the offspring of this doe will also start breeding if they can defend a territory when they are sexually mature, so many more that 11 to 25 rabbits may be produced in this one year.

Under good conditions, starting from a single pair, there were 130 rabbits after 15 months (6). This phenomenal breeding capacity is the main reason why all the killing methods that have been used on rabbits have failed to exterminate them. It is also one reason why rabbit control has to be based on fertility control rather than killing.

In rabbits, the obvious vehicle for fertility control is the myxoma virus because it is already in the wild population and it is specific to rabbits. To be effective, the chosen stain of virus has to be highly infectious, but not highly lethal, otherwise it won't be spread to many rabbits. Around 80% of rabbits will have to be infertile to ensure that the population goes down (7-8). The virus will be spread in the usual way by mosquitoes and fleas.

The good aspect of this approach is that it won't affect other species, but the bad aspect is that even weaker strains of the myxoma virus will make rabbits sick to some extent.

Mice

Mice breed even more quickly than rabbits. They can become pregnant when only 6 weeks old, and after 3 weeks produce 6 or more young. When conditions are good, they can quickly breed to plague levels. Millions of mice can decimate grain crops and anything else in their path.

Effective immuno-contraception has already been demonstrated in mice under laboratory conditions.. DNA coding for protein ZP3 from the outer layer of the egg was inserted into the ectromelia (mousepox) virus, which was then injected into the mice. In this group, 9 of 13 produced no young at all after mating, while the remaining 4 produced only 2 each. The unsterilised control group produced at least 6 pups each (7).

The sterilising effect lasts for 28 weeks, which should be long enough to prevent the development of plagues when conditions are good (CSIRO media release).

The ectromelia virus doesn't exist in the wild population, and wouldn't be released. It does show, though, that immuno-contraception can work. A virus that could be used in the field is the cytomegalovirus (CMV). It is specific to mice, is already in the wild populations, is highly infectious, and is a herpes virus spread by direct contact (Vertebrate Biocontrol CRC: The Mouse).

Foxes

No virus has yet been identified as a vehicle for immuno-contraception. Viruses which exist in the wild populations are not specific to foxes and could affect other animals, such as dogs.

Researchers therefore are testing the method used in France to vaccinate wild foxes against rabies, namely placing the vaccine in a bait. A dose is delivered orally, like the Sabine polio vaccine in humans.

The researchers have identified a number of proteins from fox sperm and inserted the relevant DNA sequence into Salmonella bacteria. The bacteria are added to a bait, and the foxes eat the genetically engineered bacteria with the bait.

The sperm proteins produce a response from what is called the mucosal immune system, lymph tissues within the mucous membrane of the digestive tract, but also the reproductive tract (9). So, when sperm enters the reproductive tract, the female's immune system will recognise it as foreign and mount an antibody attack. Of 8 females vaccinated with the sperm proteins, 5 failed to get pregnant (Vertebrate Biocontrol CRC: The Fox).

The Salmonella bacteria are a mutant strain that won't live long in the wild. They won't live long enough for foxes to infect each other. However, foxes only breed once a year, so if baiting is done before the breeding season, it should sterilise the young from the previous year who would now be ready to breed.

Researchers are still looking for a suitable virus to spread through the fox population and to carry the sperm protein DNA.

Immuno-contraception is not simple - there are still many unanswered questions and difficulties to overcome. However, it has great potential to be a more humane way to reduce and control the populations of feral animals.

The following online information on this topic is useful:
Vertebrate Biocontrol CRC: an Overview
Diagram of immunocontraception
Vertebrate Biocontrol CRC: the Mouse
Vertebrate Biocontrol CRC: the Fox
CSIRO Media Release 24/4/97

I would like to go to other documents on feral animals:
Feral animals in Australia: introduction
Poisons
Introduced diseases
Mustering for slaughter and export
Other methods (shooting, warren ripping, dogging)
Alternatives to killing

References