Here’s a guessing game. Name this animal.
The International Union for Conservation of Nature (IUCN) lists it among the world’s worst invasive species. It kills 60 million birds in Canada every year; in the US, it’s an estimated 2.4 billion birds and 12 billion mammals – that’s more than cars, windows and wind turbines combined. A 2023 global assessment found it preys on more than 2,000 species, one in six of which are of conservation concern. It has driven 73 species to extinction and now threatens 433 more.
Killing is the headline; its presence alone changes how wild animals behave, feed and reproduce. It’s also a carrier of parasites that cause toxoplasmosis, and is a reservoir for bartonellosis and salmonellosis.
Got it yet?
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I had one once. An orange one called Gumbie. I enjoyed him, though it was a non-negotiable asymmetrical relationship – when he wanted affection, it was his decision, never mine. After a good feed, he’d sit on my lap and purr so hard the vibrations reached my chest. And then, without warning, he’d jump off and disappear outside into the night.
A few weeks ago, on Harper’s Island Wetlands in Cork Harbour, a regular visitor sitting in a bird hide watched in horror as a domestic, pink-collared cat climbed up a hand-built nesting wall and pushed its face and paws into the holes.
Inside those holes were sand martins who had just paired up and begun to lay eggs. To get to this moment, they had flown a mammoth 4,000 kilometres from West Africa, where they spend their winters before coming to Ireland to breed. The journey is unrelenting and covers some of the harshest terrain on earth – the Sahel, across Senegal, Niger, Chad and Mali.
Arriving here around March, they’re already under human-made pressure: chemicals we spray on farms, gardens and urban streets nuke the insects on which they depend for food; the sandy riverbanks where they burrow their nests are disappearing through erosion and dredging. Increasingly, they rely on man-made artificial nesting walls to have any chance at all of breeding.
Harper’s Island is exactly the right kind of place for birds like these. The 30-hectare wetland in the northern part of Cork Harbour is owned by Cork County Council and run by a heroic team of dedicated volunteers. They construct hides, create shallow ponds and build nature trails. The place is home to some of our rarest species – golden plover, dunlin, redshank, black-tailed godwit, lapwing, curlew, whimbrel and oystercatcher.
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In 2022, noticing sand martins feeding over the water, volunteers built a nesting wall with 24 tunnels. Every hole was filled with breeding sand martins within the year. So they built a second wall to make 48 nesting sites. It’s a hard-won victory in a nature crisis that’s rapidly running out of them.
The domestic cat, with its pink collar, nearly ended its life in an afternoon. Predator pressure at a nest during laying can trigger immediate fear and abandonment, which makes evolutionary sense; there is no point in investing energy in rearing a nest of chicks when predators are freely roaming.
Think of what those sand martins have been through: a marathon migration, arrival in Cork, a nest site ready to go, a wetland with enough insects to rear a family, and females about to lay an egg. And then, someone’s cat was let out after breakfast.
There’s no gentle or subtle way of saying this, so I won’t bother. When it comes to endangered species, cats are a scourge. They’re among the most destructive invasive predators in the natural world, and we have somehow granted ourselves permission not only to allow it, but to stop any discussion of the fact that we need to decide how better to regulate cats and their owners.
I loved Gumbie. I never gave any serious thought to where he went when he disappeared into the dark. Yes, cats are companions – as I well know, comforting ones. But they’re also killers.
Back when wildlife was more abundant than it is now, the argument for leniency perhaps made more sense. Today, it’s reckless. In Ireland, we’re watching as species disappear in real time – not from the Amazon, or from the Congo rainforests, or from the Scottish Highlands, but from our local fields, wetlands and bogs, our nature reserves, urban parks and gardens.
What would accountability look like? In parts of Australia, cat curfews are legally enforced, and owners face fines for free-roaming pets. New Zealand is debating mandatory microchipping – which is what we have here for dogs, but not cats – and restricted roaming in ecologically sensitive areas. Some US regions require licensing. None of this is radical or unduly restrictive – it’s sensible, responsible and vital.
We license dogs and hold dog owners legally liable for attacks. When it comes to their impact on wildlife, cats are far more damaging, and there is no coherent argument for treating them differently. Sand martins that survive some of the toughest journeys on earth deserve better than to meet their end at the paw of a well-fed cat.
Around Ireland, this year’s sand martins are feeding their chicks. In a few months, they’ll leave for West Africa, and whether they’ll come back to a safe nest next spring depends partly on luck and partly whether someone remembers to keep their cat inside.
When he chose to be, Gumbie was a charming, affectionate cat. But while he was out of the house, I’ve no idea how many frogs, sparrows, starlings, wrens or baby robins he killed during his long life. We changed how we treated dogs and how we viewed dog ownership. We can – and must – do the same for the pet that poses a much greater and more immediate threat to wildlife: cats.
