Copyright 2004-2012, Sarah Hartwell

Every so often I am asked about "super-cat size" ferals by people who have heard stories that high-protein diets are causing feral cats to grow to huge dimensions. For a full explanation of why cats don't grow to giant sizes (and for the hoax giant cat "Snowball" picture), see Giant Cats. Gigantic ferals are entirely mythical. Stories of a race of large feral cats are often fuelled by anti-cat individuals or organisations in attempts to further vilify the already much maligned feral cat.

Unlike dogs, cats lack the genetic plasticity to breed to huge sizes. In dogs, a single mutant gene could explain the range of sizes, according to a study published in 2007 (Elaine Ostrander, National Human Genome Research Institute, Bethesda, US; Dr Carlos Bustamante, a member of the research team from Cornell University, Ithaca, US; Science journal). Researchers found that small dogs had the same mutation in a gene that influences size. The mutant gene is absent from most large dog breeds. The small breeds studied shared a mutant form of the insulin-like growth factor 1 (IGF-1) gene known to influence size in mice and humans. The mutant gene is present in some larger dogs; in those cases some other genetic factor must somehow override the mutant IGF-1 gene. The mutant form of IGF-1 probably arose more than 10,000 years ago.

A report of five foot long wildcats is to be found in "A General History of Quadrupeds" by Thomas Berwick (1790), but should be treated with caution. Berwick wrote: "Some Wild Cats have been taken in this kingdom of a most enormous size. We recollect one having been killed in the county of Cumberland, which measured, from its nose to the end of its tail, upwards of five feet." As well as Berwick's information being secondhand at best, animal sizes (lengths and weights) were routinely exaggerated by hunters and by farmers in order to make their kills/livestock seem more impressive.

In August 2012, Stephen Harris, Professor of Environmental Sciences at Bristol University, suggested that feral cats in Britain are growing to large sizes to fill the "large predator" niche once occupied by wolves. He claimed domestic cats can be as long as 4ft from nose to tail-tip in Britain and that he had seen domestic cats exceeding 5ft in Australia. In Britain, their size is assessed by analysing indistinct photos rather than by shooting and measuring the animals themselves. There is no scientifically verifiable evidence supporting the Australian claims as the carcases of purported "giant ferals" shot in Australia have tended to disappear. Forced perspective and photographic angle gives the impression that animals are larger than they really are.

The genes for huge size simply don't exist in cats, and regardless of improved diet, cats have stayed pretty much the same size since they were first domesticated. The largest breeds of domestic cat are the Maine Coon and the Ragdoll, though these are generally under 20 lbs - hardly gigantic - and are bred for mellow temperaments. Even crossing domestic cats with a larger wild species such as the serval or jungle cat has only slightly increased the size. A number of F1 and F2 hybrids reach impressive sizes, but the need to back-cross to domestic cats to preserve the domestic temperament also proves a limiting factor on size.

There have been a few reports of giant, but not obese, domestic cats including a 30lb cat with a low voice (suggesting pituitary giantism). Rare abnormalities such as Klinefelter syndrome or acromegaly (pituitary giantism) can also result in over-sized individuals. Pituitary giantism brings with it a host of health problems including deformity, joint problems and shortened life expectancy; it does not create huge ravening felines. Far from being more effective predators, affected individuals would have a hard time surviving in the wild due to the harmful effects of these conditions.

Another claim is that high protein diets are causing feral cats to grow larger. Firstly, where are the feral cats getting these high protein diets? Most are hunting the same prey and getting the same levels of protein as their predecessors. Some are being fed by cat lovers, but they are eating the same balanced cat foods that domestic cats eat with the same level of protein that we feed to our normal-size pet cats. Many of the ferals living on handouts have also been neutered as part of the deal, so they won't be breeding kittens of any size. Others are living on scraps and restaurant leftovers; these scraps are probably high in fats and carbohydrates, rather than high in protein.

The idea that high-protein diets have caused successive generations of feral cats to grow huge is also erroneous. Cats metabolise fats and proteins, but not carbohydrates. Their diet must be high in protein in order for them to reach a normal size; restricting their diet or eating poor quality foods stunts normal growth. We are seeing feral cats reaching normal cat-size rather than seeing stunted cats; but we are certainly not seeing an emerging race of super-ferals.

What happens if cats are given very high levels of protein? If the diet contains high levels of protein but is deficient in other essentials, we end up with unhealthy cats with vitamin and mineral deficiencies or overdoses. Too much or too little of certain vitamins can be lethal. Too little calcium, usually from eating nothing but muscle meat, causes bone problems. Too much liver causes Hypervitaminosis A and skeletal problems. Too little vitamin D causes rickets. Cats need balanced diets, not just protein. Cats generally regulate their food intake (pet cats overeat through boredom) and feral cats expend much of their energy intake in hunting and foraging activities. A feral cat that gets a high protein diet will probably regulate its intake by hunting less often for food. It may be fitter, less scrawny and not stunted, but it won't be super-cat sized and nor will its offspring be super-cat sized. Abundance of food means they may breed more successfully and more kittens may survived, but the increase will be an increase of numbers, not an increase of individual dimensions.

In short, a high-protein diet is not going to lead to gradual increase in stature to create super-cat size animals. The effect of too much good food and the feline inclination to conserve energy can be seen in the overweight housecats of Britain and America. A few ferals living on handouts rather than actively hunting might become overweight. As with humans, obesity can cause reproductive problems.

To summarise: while well-fed feral cats will not be scrawny like their hungrier relatives, they do not have the genes to allow them to grow into a race of huge size cats. However, it suits organisations that would prefer to see feral cats exterminated (and see pet cats severely restricted) to perpetuate the myth of feral monster moggies able to dispatch brown hares and even lambs and preying on domestic pets. Some of the damage attributed to supposedly over-sized feral cats is actually caused by stray and feral dogs; many people prefer to ignore the fact that "man's best friend" is still a wolf at heart.

Tales of feral cats attaining giant sizes have been spread in Australia, where there is a vociferous anti-cat lobby, in the USA (where an ill-advised book portrayed feral cats as huge and dangerous) and in Britain. A few years ago, a faked photo of a man holding a supposedly giant cat ("Snowball") did the rounds accompanied by a story that the cat was due to the effects of mutagens on feral cats. The photo is known to be a hoax and story of the photo and its originator is reported on numerous websites.


Although Australian feral domestic cats are sometimes described as twice the size of normal domestic cats, feral domestic cats in Australia are within the normal domestic cat size range. As with many species, a few exceptional individuals occur, but are not representative of the typical feral cat. Giant domestic cats sometimes occur due to genetic abnormalities (which often cause sterility) or pituitary abnormalities. There have been reports of Australian feral cats shot by farmers that reach 1.1 metres from nose to tail and suggestions that the cats are breeding fast enough that they are evolving into super-cats.

A supposed big cat ("black panther") in Dargo, Gippsland, Australia was shot by a Melbourne deer hunter named Kurt Engel who claimed the 1.5 metre (6 ft), 35 kilo cat had charged him. As with many photos, the cat is in the foreground and perspective makes it appear larger in proportion to the hunter. The body was photographed and disposed of, but the apparently 600 mm (26 inch) tail was sent for DNA testing at Monash University and shown to be a feral domestic cat. The tail was sent without vertebrae and could have included extra fur from the back which makes accurate size estimations difficult. A cat's tail is normally 30 cm (12 inches).

The partially decomposed carcass was examined by a Rural Lands Protections Board vet, Dr Keith Hart, in 2006. The body was 34" (just under 3 ft) and the tail 14" (48" total length). Even considering the state of decomposition, this is substantially smaller than the size claimed by Engel. Although the measured size is within the size range of the smallest subspecies of leopard (Pantera pardus nanopardus of Somalia), the occurrence of an abnormally sized individual does not indicate that Australian feral cats are mutating into giants. For comparison, a Maine Coon has been recorded as reaching 49 in (121cm) total length (equalling the Gippsland specimen's size) and tails of 13" - 14" have been recorded in domestic cats.

The problem with Engel's photographs is the same as that with "Hogzilla" the giant wild pig shot in the USA. Use of perspective and the absence of a body allowed the hunter to exaggerate the pig's size. When the body was exhumed, it was found to be abnormally large, but not as large as claimed by the hunter.

Big cat researcher Mike Williams claimed it was extraordinary that Australia has produced a domestic cat mutation the size of a leopard. There is currently no evidence that this is a size mutation and not the result of a medical condition in a single individual. Karyotyping would be required to rule out chromosomal abnormalities that lead to abnormally large domestic cats while giantism due to a tumour of the pituitary gland is another possibility.

Although this individual cat may be an abnormally large individual, without the whole corpse, any claims of leopard-size are hyperbole as leopard subspecies are variable in size ranging from Somalia's relatively small "nanopardus" through to the more familiar large leopards. To be meaningful, suchs claims should be accompanied with reference to the leopard subspecies. Scientists claim this abnormally large cat is proof that Australia feral cats grow to enormous proportions and present a significant threat to small wallabies.