Animal Control
Any animal has the potential to become a pest when introduced to a new environment. Those animals then need to be controlled. There are a number of ways that people use to reduce the pest population. There are plenty of examples of animals that have become pests in New Zealand and the focus of large control programmes. Possums, rabbits and mustelids are major pests in New Zealand, that affect native flora and fauna as well as farmland productivity.
Problems with animals are numerous. Rabbits affect pasture quality and livestock due to their extensive feeding and burrowing habits. Possums consume thousands of tonnes of vegetation a night in New Zealand as well as being a vector of Bovine tuberculosis. Mustelids attack bird species, particularly ground dwelling birds, which in many cases are highly endangered.
Trapping is a common method for animal control. This method is used when it is not appropriate to use chemicals. Trapping is also a method of monitoring the pest population in an area. This gives a residual trap catch rate.
There are many chemical methods used to control animal pests. Poisons can affect animals in different ways. If you are controlling a number of pests there may be a variety of bait stations and baits laid which need to be monitored and replenished at different times and rates.
Shooting is an effective method of controlling pests like possums and rabbits. It is however labour intensive and not used as frequently as trapping and baiting. In places like the South Island of New Zealand there are annual rabbit shoots that can net tens of thousands of rabbits – such is the size of the problem.
Possums were introduced for the fur trade in New Zealand but what a disaster. Endangered in Australia the reverse is true in New Zealand. The New Zealand climate is ideal and they can breed up to twice a year. There are no natural predators in New Zealand for these animals. In New Zealand the plants have never had to develop defence mechanisms, so all are palatable to the hungry possum. This means that native trees like the rata and pohutukawa are threatened by the possums eating behaviours. They can also vector a disease of cattle – bovine tuberculosis which is a significant disease for farmers to be faced with.
Rabbits were introduced to NZ in the 1800’s as part of the fur trade. They needed to be introduced several times before they established. Once established in the environment they soon became a problem. Extensive feeding and burrowing in pasture destroys the grass and creates hazards for livestock in those paddocks. Rapid breeding increases the population and the problems. They have developed immunity to diseases like Rabbit Calicivirus which for a brief time managed to reduce the populations in the South Island.
Three types of mustelids were introduced to New Zealand as a way of controlling rabbits. They have become as much of a problem as the animal they were introduced to control. Ferrets, weasels and stoats feed on the eggs and chicks of birds. In New Zealand, many birds like the kiwi are ground dwelling which makes them easy targets for these predators.
About the author: Bevan Jones is biosecurity, plant control and animal control expert in Auckland, New Zealand.