Domestic cats are highly motivated and skilled predators. They possess very strong hunting instincts, and will actively hunt and kill prey regardless of how well they are fed. The role they play in the decline and even extinction of many species of native wildlife is often underestimated. They prey on small vertebrates such as birds, mammals, amphibians and reptiles. Feral and free roaming cats are known to kill billions of animals annually across continents like Australia and the United States of America.
One study from the Smithsonian found that cats likely kill between 1.3 and 4 billion birds per year in the US alone. Their impact on wildlife in Europe is probably predictably similar, although fewer studies have been conducted. With nearly a quarter of a million households in Ireland reported to own a cat, not to mention free roaming farm cats and feral cats, their impact on Irish wildlife is something that requires further investigation.
Cats are the primary extinction driver of at least 33 vertebrate species and are known to be responsible for the demise of many more species across the world; examples include the endangered black stilt in New Zealand, Okinawa woodpecker in Japan and nestling red-tailed black cockatoos in Australia. In Ireland, cats are known to prey on protected species such as the pygmy shrew and the threatened ground-nesting corncrake.
It is difficult to put an exact number on the amount of wildlife killed by cats. Nonetheless, estimates by the Australian Wildlife Conservancy in their summer report of 2012/2013 put it between five and 30 animals a day. Multiply that by the number of feral cats worldwide and that is potentially tens of billions of native animals killed every year. This has a real impact on native wildlife, which are quite often already under stress from habitat destruction, climate change and pollution to name just a few. The number of native animals killed by cats in Ireland may not be in the billions, but it is still probably staggeringly high given the popularity of cats in this country.
Compounding the issue of wildlife decimation is the fact that cats are prolific breeders. They have no set breeding season, can have multiple litters each year and are sexually mature from six months old. This results in escalating numbers of cats, playing a critical role in the decline of native fauna. Trap neuter and release (TNR) programs are hugely popular in Ireland with the assumption that they reduce cat numbers. However, studies show that given the high intrinsic growth rate of cat populations TNR programs have little impact on free roaming or feral cat populations. Given this information stronger measures should be considered for reducing cat populations and research into alternative approaches should be encouraged.
Other countries are waking up to the destructive nature of cats and have introduced various control measures. There are entire suburbs that are pet cat free. There are feral cat-free zones where large predator-proof tracts of land have been fenced and people are attempting to eradicate cats from off-shore islands to protect susceptible prey species. These feral cat-free zones may be the last hope of many endangered animals. Other options to reduce the impact of cats include traditional baiting, trapping and shooting. These methods come with their own difficulties as cats are notoriously elusive, and hard to track and hunt.
The issue of cat control, particularly using traditional methods is as complex as it is controversial. They are a much loved and popular pet that have featured greatly in our history since their domestication in Egypt thousands of years ago. This results in the need for innovative approaches. In Ireland, farm cats are seen in a positive light as they prey on mice and rats. Cat control in Ireland could therefore include encouraging the presence of barn owls in rural settings as an alternative to cats. Barn owls are a native predator and are known to prey almost exclusively on rodents. According to biologist Mark Browning, one family of barn owls can take 3000 rodents in one breeding season alone.
In addition to these active control measures, education surrounding responsible cat ownership is needed to reduce the impact of pet cats. Cats that are kept indoors or are only allowed in contained outdoor runs pose little threat to wildlife. It is the free roaming cats and feral cats that are destructive. Keeping your cat indoors will also likely cause them to live significantly longer, since the risk of being killed by cars or wild animals is eliminated. Indoor cats are also far less likely to contract diseases like feline immunodeficiency virus (FIV). Education surrounding the impact all cats have on wildlife may be the key to lessening their damage. Here in Ireland more research is needed to explore the impact cats have on Irish wildlife, and if necessary to find suitable long-term solutions.
Natasha Ballard – Science Writer