The active ingredient in these products is brodifacoum or bromadiolone. For some species, particularly mice and voles, enough active ingredient to cause death can be eaten at one feeding. Resistance to second-generation anticoagulants is not widespread. However, at least one group of resistant House Mice has been found in Toronto. Bait shyness or avoidance Hazards to non-target species Baits Palatability, in terms of the preferred grain carrier and the placement of baits, are specific to the species.
Palatability is discussed in some detail in the technical pages for each class of rodenticide below.
However, there are a number of general points concerning the palatability of baits that can be made here. Rodents have highly developed senses of taste and smell, and both play a role in the acceptance of baits. Baits that taste or smell unusual may be rejected or rodents may feed only sparingly on them, with the result that a less than lethal dose is eaten. Similarly, volatile chemicals such as herbicides, insecticides, fertilizers, and paint thinners can create off-flavours or odours to baits if they are stored in close proximity. Odours that cause rodents to reject baits may well not be detectable by humans.