Rodenticides are toxic chemicals used for the control of rats, mice and other pest species of rodents. Poisoned baits are the most generally effective and widely used means of formulating rodenticides, but some are used as 'contact' poisons (such as dusts, foams and gels), where the toxicant adheres to the fur of the animal and is ingested during subsequent grooming, while a few are applied as fumigants to burrows or infested premises. To respond to the development of resistance to acute toxic poisons, these have been replaced by slower acting chemicals, such as anticoagulants, that cause rodents to bleed to death. These second-generation rodenticides have helped control pest numbers since their introduction in the 1980s, but their potential for bioaccumulation means that they have become concentrated in the bodies of rodent predators. Serious declines in populations of predators would curb the rate of natural control of rodents, requiring even more use of rodenticides.