Confining domestic cats indoors to protect wildlife, as some campaigners are calling for, will have a major impact on the animals’ own welfare, according to experts at the Katten Kenniscentrum Nederland in a new report.

There are more than three million cats in the Netherlands which, together with an unknown number of feral cats, are said to kill millions of birds, rodents and small invertebrates each year. And, campaigners say, keeping the cats inside is the best way of reducing their impact.

However, the report, which will be presented to MPs later this week, says domestic cats will suffer chronic stress and boredom if confined indoors, particularly if more than one cat lives in the same home, Trouw said on Monday.

Cats, by instinct solitary hunters, need to be able to go out to let off steam, the KKN experts say.

Nevertheless, the KKN backs compulsory microchips, which may be introduced in 2026, and says castration for cats who go outside should also be on the agenda.

This is because allowing domestic cats to reproduce will increase the feral cat population, particularly in the countryside, and feral cats make the best hunters.

Research on the Wadden Island of Schiermonnikoog, for example, indicates that the estimated 50 feral cats kill some 6,000 birds a year.

Cat owners can also fit their animals with brightly coloured collars which, the organisation says, are better than collars with bells. There is no evidence that the bells warn birds of the cat’s presence, but the loud noise is an irritant to the cats themselves.

Protect species

Tilburg University researchers said in 2019 that cats are a risk to 370 protected species and that this means their owners are breaking the law by allowing their pets to go outside.

Others have called for cats to be kept in at night, particularly during the breeding season.

The centre earlier carried out a fact check on reports that cats in the Netherlands kill 18 million birds a year and found no direct evidence for the claim. It said the figure seems to be based on estimates, the number of feral cats and research abroad.

Nevertheless, with approximately 3.16 million cats in the Netherlands, there are too many, the centre’s Maggie Ruitenberg told the AD on Monday. “In 2013 we had around two million,” she said. “And we cannot deny that cats can be a problem.”