High rat populations will prevent forest covenants reaching their potential. Uncontrolled forests may have seven or more rats per hectare, each eating seeds, eggs, chicks, geckos, skinks and invertebrates. They are hard to spot but the lack of birds may well be an obvious sign of high rat numbers.
Trapping can be used in smaller areas (less than one hectare), but is not recommended for larger covenants as the amount of traps needed and the time required to check them is unworkable. For large areas, set bait stations on trees at eye height. Use a grid formation with stations spaced 100 metres apart to ensure adequate coverage.
Full time control takes up more time and toxin than seasonal control but will keep rat numbers low year round. Bait stations need to be constantly filled with a suitable toxin. Bait stations can be topped up monthly once you have achieved a significant reduction in rat numbers.
Seasonal control is when bait stations are only used just prior to the breeding time for birds, reptiles and invertebrates. Generally speaking, baiting should start mid to late September so that numbers are very low by the beginning of November. Having low rat numbers at this time allows the vast majority of birds and other native species to have a successful breeding season. Rat numbers will build up again but seasonal control suppresses their numbers when native species are at their most vulnerable.
Results can often be achieved with only two or three bait station fills of approximately 200 gms of toxin - less effort and toxin, and big biodiversity gains.
For effective rat control, possums numbers need to be at low levels otherwise they, rather than the rats, will take the toxin. If possum numbers are high, deal to them first, using a broadificoum-based toxin, or, if possible, by trapping. Once possum control is done, a lower toxicity bait with minimum secondary poisoning risk (such as Possum pindone) can be used to deal with the rats.