Amsterdam is planning to ask cat owners to hang a bell or collar around their pets’ necks when they go outside, to warn birds and other wildlife about their presence.

The proposal is contained in a plan for ensuring the capital remains an “animal-friendly” city that is currently being discussed by officials. 

The cat, officials say, is one of the few animals that is allowed to roam the city unsupervised despite posing a danger to birds in particular. According to researchers at Wageningen University, domestic cats kill some 18 million birds a year.

Amsterdam will also start a campaign to encourage cat owners to have their animals chipped and sterilised to keep the feral population down and has agreed that feral cats will no longer be released into “ecologically vulnerable areas” once they have been caught and sterilised. 

Various efforts have been made over the years to curb the problems caused by domestic cats. In 2021, Dutch foundation Huiskat Thuiskat went to court in effort to force the government to take action against people who let their cats roam freely outdoors.

The foundation has welcomed the move to introduce bells but says research shows they only reduce a cat’s prey by 33% to 50%.

Ecologists have also called for a curfew for cats. In 2019, a paper by Tilburg University environmental law professors Arie Trouwborst and Han Somsen in the Journal of Environmental Law argued that the domestic cat (Felix Catus) is posing a serious threat to some 370 species in the Netherlands.

Under the European Bird and Habitat Directives countries have a legal obligation to protect wildlife, so allowing cats to roam and kill is illegal, the researchers said.

The national government was planning legislation to ensure all domestic cats in the Netherlands are chipped and registered to allow pets to be reunited with their owners more quickly, and help deal with the problem of feral cats.

There are some 2.9 million pet cats in the Netherlands and every year 60,000 are reported missing. Looking after stray pets costs local councils €4.8 million a year.