Recently, despite the presence of numerous feral/stray cats in Singapore, there have been many rat infestations including a prominent and highly visible one near Bukit Batok MRT.
The domestic cat was originally kept for pest control purposes: that is, in order to hunt mice and rats. Cats have a natural hunting instinct, which makes them also highly efficient predators of many other small animals including birds and other wildlife.
So why are these ruthless predators not doing anything to the rats?
The obvious problem is with people who are feeding, and in many cases over-feeding, the cats (see also http://lifebesiderunning.blogspot.sg/2014/12/of-rats-cats-and-dogs.html).
In my neighbourhood, some cats are fed TWICE a day. Another idiot gives cats a full human-sized bowl’s worth of cat food (weight of human: >50kg, weight of cat: <5kg, do the math). Yet other idiots try to feed cats rice, which is inevitably ignored and then eaten by pigeons, mynahs or rats (cats are obligate carnivores, they can’t digest plant foods).
Members of the cat family from lions to domestic cats are all heavy sleepers and layabouts; they don’t move much unless absolutely necessary. If cats are well-fed, they have no incentive to hunt, and just spend their days sleeping and sitting around waiting for the next meal to be delivered to their doorstep (whereas humans actually have to work to support themselves).
So for biological control to be effective, and for cats to return to their natural and original lifestyle of hunting and eating rodents, feeding should only be treated as a supplement and incentive for the cats. Therefore, cats should be fed at most one meal per week, with the remaining diet composed of rodents and birds (plenty of inexperienced young mynahs around).
This would not only reduce the rat problem, but also increase the value of cats as biological pest controllers, rather than cats being just another pest problem.