Rodents
In Australia, a number of rodent species are agricultural pests. Two species, the house mouse (Mus domesticus) and black rat (Rattus rattus), were introduced around the time of European settlement. House mice are found throughout agricultural cropping areas, and around sheds and houses. When conditions are favourable, their numbers can increase to plague levels. Black rats are found throughout temperate and tropical Australia in human-modified environments.
Several native rodent species may also be pests in some situations. The canefield rat (Rattus sordidus) and the grassland melomys (Melomys burtoni) have become serious pests of sugarcane in Queensland. The canefield rat also causes problems in grain crops in south-east Queensland. Another species, the pale field-rat (Rattus tunneyi), causes damage to young trees in hoop pine plantations. In the Ord River area of Western Australia, the long-haired rat (Rattus villosissimus) can cause crop damage when it is at plague densities.
More detailed information on rodent management is contained in the Bureau of Rural Sciences' publication 'Managing Vertebrate Pests: Rodents' - Caughley, J., Bomford, M., Parker, B., Sinclair, R., Griffiths, J. and Kelly, D. 1998 ($A24.95).
"Managing Vertebrate Pests: Rodents" might sound a bit dry and technical as a title, but this book actually contains information which could surprise many people.
For example
Although rats and mice have caused many millions of dollars of damage to Australia's farm exports through this century, at the time of writing the book only Western Australia, Victoria and the Northern Territory had passed laws to declare some rodents as pests. In other states and territories, there is still no legal requirement that they be controlled.
Australia's approach to this pest problem has tended to be "out of sight - out of mind". All too often, says the book, Australian land/resource managers still resort to "crisis management" of rats and mice when a plague occurs - acting only when populations of rodents are large enough to be causing obvious damage. This doesn't work. "Crisis management is generally unsuccessful in limiting further damage, since rodent numbers rapidly increase to pre-control levels due to immigration and breeding".
The main culprits are introduced species - the so-called "house mouse", and the "black rat". But in some areas of Australia, native species of rodents can be pests - for example, the canefield rat in north Queensland.
There is still plenty we don't know about how to control rats and mice. For instance, Australian land managers and resource scientists need to collect more information on how to link rodent numbers to the potential impact, or damage, they can do.
The book addresses this problem by outlining practical and effective ways for farmers and land managers to estimate rodent populations and the damage they cause.
It also outlines effective control techniques for rats and mice. These include poisoning, making the environment less sympathetic ("habitat modification"), trapping, and the best overall method of controlling rodents - a combination of various approaches. The control techniques are clearly illustrated by a number of case studies.
One of the control techniques mentioned is to encourage birds of prey (who feed on rats and mice) to live and breed on farms with a rodent problem.
Managing Vertebrate Pests: Rodents gives an up-to-date summary of the economic and environmental damage caused by rats and mice.
It estimates, for instance, that each year since 1900, mice have caused $13 million worth of damage to crops. Worse still, in the last 20 years, the annual damage figure is closer to $26 million. And these are "very approximate and conservative" figures, says the book.
In a graphic example of the damage and contamination caused by mice and black rats to stores of grain and other produce, these rodents consume about 10% of their body weight every day - which means that an adult rat eats about 30 grams every day, or ten kilograms of food a year. And an infestation of only ten black rats produces some 146,000 droppings and 54 litres of urine a year.
The book outlines nine problem areas where we need to take more action to control rodent pests. Concluding this chapter, the authors sound this warning: "Addressing these deficiencies is essential for achieving effective management of rodents and the damage they cause to agriculture and the environment".
Purchase the publication: Managing Vertebrate Pests: Rodents