animal pests controlling

Some animals can pose problems in the environment and therefore need to be controlled. Any animal has the potential to become a pest when introduced to a new environment. In New Zealand, there are plenty of examples of animals that have become pests and the focus of large control programmes. Possums, rabbits and mustelids are major pests of the environment 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 can be used for animal control. This method is also used when it is not appropriate to use chemicals. Depending on the animal will depend on the type of trap used. Trapping is also a method of monitoring the pest population in an area and gives the residual trap catch rate.

There are many chemical methods used to control animals. Depending on the pest that you want to control will depend on the chemical used. Chemicals can affect animals in different ways therefore 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 another commonly used method of controlling animal pests. For possums and rabbits it is however labour intensive and not used as frequently as trapping and baiting. In the South Island of New Zealand the rabbit problem is so bad that there are annual rabbit shoots that can net tens of thousands of rabbits.

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, like possums were introduced to NZ in the 1800’s as part of a fur trade. They were even introduced multiple times before they flourished. Once they were flourishing it was soon apparent that people needed to think about how to control them as they quickly became a problem. Extensive feeding and burrowing in pasture destroys the grass and creates hazards for livestock in those paddocks.

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.