The introduction of the domestic cat, Felis catus, to new continents and islands has created a major global conservation problem. As a non-native invasive species, the cat’s predatory actions have been a direct or contributing factor in the permanent loss of numerous vertebrate species. The severity of this issue is often misunderstood because it is largely driven by feral populations and concentrated in vulnerable ecosystems. Understanding the scale of this impact requires looking beyond the house pet to the ecological damage caused by wild-living cat populations.
Verifying the Extinction Count and Identifying Key Victims
The figure of 33 species driven to extinction by cats is a widely cited number that is specific and geographically focused. This number refers specifically to endemic bird, mammal, and reptile species on islands whose extinctions were caused or contributed to by introduced feral cats. The total global impact is much higher, with cats implicated in the extinction of at least 63 species worldwide.
The true scale of the problem is evident in regions like Australia and New Zealand, where native fauna evolved without similar mammalian predators. In Australia, cats have contributed significantly to the extinction of over 20 endemic mammal species since European settlement, including small marsupials like the Lesser Bilby (Macrotis leucura) and the pig-footed bandicoots (Chaeropus ecaudatus). The most famous example is the Stephens Island Wren (Traversia lyalli) of New Zealand, a small, flightless songbird entirely wiped out by a burgeoning feral cat population in the late 19th century.
The Mechanics of Feline Predation and Ecological Impact
The feline hunting mechanism is destructive to native wildlife because it is driven by instinct rather than hunger. Domestic cats are opportunistic predators, often engaging in “surplus killing,” meaning they will continue to hunt and kill prey even when fully fed and satiated. This behavior results in a chronic, low-level predation pressure that is continuous and highly damaging to populations that already have limited numbers.
Feral cat populations exacerbate this ecological pressure through their high reproductive capacity. Female cats can become fertile as early as five months and can produce an average of two or three litters each year. This accelerated breeding leads to rapid population growth, dramatically increasing the number of predators on the landscape. This constant threat ultimately causes population decline and collapse in vulnerable species.
Feral Cats and Island Biogeography
The primary drivers of extinction are feral cats, which are the descendants of abandoned or lost domestic pets that have reverted to a wild, unsocialized state. Unlike owned pets, these feral populations sustain themselves entirely by hunting and scavenging, often reaching high densities where human subsidies are present. They are now established across nearly 99% of the Australian continent and many of the world’s islands.
Island ecosystems are disproportionately affected due to a phenomenon known as the “island syndrome.” Native island species, having evolved for millennia in isolation without ground-dwelling mammalian predators, often exhibit “predator naiveté,” meaning they lack the instinctual defensive behaviors like fleeing or hiding. Furthermore, many island birds evolved to be flightless or ground-nesting because flight was energetically costly and unnecessary in the absence of danger. This combination of small population sizes, specialized niches, and a complete lack of co-evolutionary defenses makes island fauna exceptionally susceptible to the intense predatory pressure from introduced cats.
Conservation Strategies for Native Wildlife
To combat the pervasive threat of feral cats, conservation efforts focus on creating and maintaining predator-free safe havens for native species. Exclusion fencing, which involves constructing large, cat-proof enclosures on the mainland, has proven highly effective, allowing threatened mammals like the Bilby to recover within these protected zones. Australia also manages a network of offshore islands from which cats have been successfully eradicated, enabling the successful reintroduction of native species like the Western Barred Bandicoot.
Targeted removal programs are implemented using advanced, humane methods like species-specific baits and remote-sensing technologies. Community education plays a significant role by promoting responsible pet ownership, including desexing, and encouraging the containment of domestic cats indoors or in secure outdoor enclosures. These combined strategies are aimed at reducing the source of the problem and protecting the most vulnerable populations.