A lot of people ask, if I get another pet will it get along with my cat? The corollary to this question, if I get a cat will it get along with my existing pets, is also of interest to some folk. There is no simple answer to these two questions, but there are some facts to consider that might help forecast the results of such interspecies interactions:
While there can be some very harmonious marriages of species, sometimes the result of the mix can be damaging – or even lethal – to one or both animals.
Cats and Pocket Pets
Mice, rats, and other small varmints should only be kept in a home with cats if you can guarantee to provide for their welfare. However interested and benevolent your cat may appear to be toward the rodent or rabbit, don't believe it. Cats tell wicked lies about such things and just can't help themselves. Nature has programmed cats to chase after and pounce on small animals that run rapidly. If you do want to have mice or rats in the same house as a cat you have to make sure that:
It is said that rats over 500 grams weight can take care of themselves when it comes to cats, but I wouldn't trust it.
I have rats that grew up with cats. The rats love the cats (of course), and run to see them, even throw food out of their cage for the cats. The cats show great interest in the rats, too, but their interest is reminiscent of the Big Bad Wolf's interest in Little Red Riding Hood. One false move and the rats would be gone.
Cats, Birds, and Fish
Pretty much everything I have said about pocket pets applies to birds and fish, too. The birdcage or fish tank should be firmly secured, and small havens should be well out of harms way. Fish and cats are not too bad a combination as long as you (literally) keep a lid on things – but cats and birds are a more tentative mix.
The problem is that while fish usually remain untroubled by the periodic, riveted attention they receive from the cats, birds are not immune to their predatory onlookers stares and can be really quite troubled. Also, it's a little easier for a cat to tip over a birdcage than to heave over a fish tank. Larger birds, like Macaws, may not be so intimidated by cats, and may even give cats some reasons for concern, but small birds, like parakeets, are definitely at risk of intimidation, and even injury or death. And they usually know it. Not a very nice predicament for the caged ones and one to be avoided at all costs.
Cats and Snakes, Reptiles, and Chelonians
There is no possibility of social harmony between cats and the above species. Reptiles should be housed alone and cats should be protected from them. Larger constrictor snakes can easily kill cats. Reptiles, like iguanas, have sharp teeth and can be very aggressive. Tortoises can look after themselves in ways for which they are famous, but why allow them to be hassled by a probing cat who takes perverse pleasure in seeing the chelonian's head go shooting back under the shell.