Dog owners need pooper scoopers, while cat owners have it a little easier: Their pets are fastidious creatures that will cover their waste either in the litter tray or out in the garden. This is an instinctive behavior for cats, and no training is required.
Cats in the Wild
Feral cats will cover their poo to prevent its scent from attracting unwanted attention from predators and competitors. Females with young kittens are particularly fastidious. When colonies of feral cats live together, it is common for the dominant cat to sometimes leave his waste uncovered to advertise his presence and dominant position. Cats are territorial; he is letting others know that this territory belongs to him.
In the wild, mother cats never go to the toilet close to where they keep their kittens, but the kittens automatically dig holes for their own poo. Domesticated kittens may learn to use the litter box by watching their mother, but even young kittens will automatically dig in kitty litter or sand if you place them there after eating. They are quite fussy about covering it up afterwards and often do far more moving of litter than is necessary.
Cats in the Home
Domesticated cats know there are no predators in the home, but they still cover their poo -- regardless of whether they are indoors-only cats with litter boxes or cats that are let outdoors and dig in the garden soil. It may be that the cat regards the owner as the dominant member of the household; in homes with several cats, the dominant one will sometimes leave his waste uncovered.
Cats Not Covering Poo
Macho tomcats will sometimes leave uncovered poo as an advertisement for the ladies. Sometimes a cat will not cover its waste because of health problems or stress. Stress can arise if there are drastic changes to the living environment, such as introducing a new cat to the household, changing household routines or moving the litter box to a place that is not as quiet as the old one. If you do not keep the litter tray clean, a cat might not only leave poo uncovered but leave it on the floor instead of the tray.