Natural-born killers wreak ecological havoc

According to the French Novelist, Victor Hugo, “God has made the cat to give man the pleasure of caressing the tiger”. It’s an apt description of these scaled-down apex predators. The fearsome toll they take on wildlife may come as a shock to many cat owners, but it’s well understood by ecologists, as I discussed in the Irish Examiner in April.

WHILE WE MAY think of them as cuddly and adorable, cats “both domestic and feral” are the ultimate natural-born killers, finely tuned by evolution with the agility, stealth and hunting instinct to wreak havoc on wildlife on a huge scale.

Globally, one in seven of all modern bird, mammal, and reptile extinctions are directly attributable to free-ranging cats on islands, according to the “Red List” of the International Union for Conservation of Nature.

A study in the United States estimated that cats kill between 1.4-4 billion birds annually, with two-thirds of these kills attributed to un-owned or feral cats. A recent UK report found cats responsible for killing between 160-270 million small animals a year, a quarter of which were birds, but these are likely to be significant underestimates.

A pandemic craze for buying cats, along with cat videos on social media has seen a significant increase in their overall numbers. It’s reckoned there are around 750,000 cats in Ireland and 12 million in Britain. And some owners who tired of their new cats after lockdown ended simply dumped them, leading to a rise in feral cat populations.

And, with the nesting season once again underway, this time of year young birds just learning to fledge offer easy pickings for cats.

There are few hard numbers on the likely toll taken by cats on Irish wildlife, but assuming the ratios are similar to Britain, they probably dispatch around 22 animals each annually, bringing the expected Irish death toll of birds and small mammals at the claws of cats to more than 16 million a year.

The State of the World’s Birds report published last year identified that 63% of Irish bird species are in serious decline, a figure significantly worse than the global average. Predation by cats is by no means the most serious threat they face, but it is especially acute in urban and suburban areas, where birds would otherwise escape from ongoing habitat loss, hedgerow clearances, and pesticide usage in many parts of rural Ireland.

A number of local authorities across Australia last year moved to introduce bans on cats being allowed to roam after dark. Cat owners face fines of $200 if their animals stray into council-owned bushland, but moves are also being considered to extend the ban to footpaths, roads, and verges, unless the cat is on a leash.

Australia has an acute problem with feral cats, with each one reckoned to kill on average 740 wild animals a year. Every day in Australia, domestic and feral cats kill around two million reptiles, three million mammals, and a million marsupials, as well as an unspecified number of birds.

While to their owners they can be a loving companion, once set loose, cats are a dangerous invasive species that need to be closely supervised. A program to trap and neuter feral cats (which are then released back into the wild) is also underway in Australia.

The kiwi, New Zealand’s famous flightless bird, is especially vulnerable to feral cats, rats, and weasels. The New Zealand government spends tens of millions of dollars annually clearing invasive species from its many small islands. Since Europeans first landed in both Australia and New Zealand, a wave of invasive species that accompanied them, from cats and rats to rabbits, have triggered waves of extinctions of vulnerable native species. Undoing even some of the damage is a Herculean task.

Last August the German town of Walldorf ordered all residents to lock their cats indoors throughout the summer for the next three years, in a last-gasp bid to save the ground-nesting crested lark, of which only three breeding pairs remain in the district. Owners face a €500 fine if their cat is caught outdoors; if it kills an endangered lark, the fine rises to a whopping €50,000.

While there are no indications as yet that Irish authorities are prepared to consider such draconian steps to curb killer kitties, there are some practical steps cat owners can take to greatly reduce the risks to wildlife:

The most effective is a dusk-till-dawn curfew, as both cats and birds are most active at these times of the day. The evidence on attaching a bell to your cat’s collar is inconclusive. An alternative is to fit your cat with a colourful bib, which will help alert birds to its presence.

Simply playing with your cat for at least 10 minutes a day has been shown in studies to reduce its urge to hunt. Some research also suggests feeding pet cats with a diet that includes meat-derived protein may help dampen the primal instincts of these pint-sized killing machines.

ThinkOrSwim is a blog by journalist John Gibbons focusing on the inter-related crises involving climate change, sustainability, resource depletion, energy and biodiversity loss
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