House that feline

As if Australians need someone to remind them of the danger to wildlife of Felis catus – the domestic cat.

CSIRO Publishing’s 2019 book Cats in Australia – based on a re-examination of existing literature about cats – suggests that all F. catus here, house and feral, are responsible for up to millions of bird, reptile and small mammal deaths each day.

Cue a new study from the US that confirms hunting by house cats can have big effects on local animal populations because they kill more prey, in a given area, than similar-sized wild predators.

This effect is mostly concentrated relatively close to a pet cat’s abode: most of their movements are within a 100-metre radius of their homes, usually encompassing their yard and a few of their nearby neighbours’.

For the new study, researchers from North Carolina State University and the North Carolina Museum of Natural Sciences collaborated with scientists and citizen scientists from six countries to collect GPS cat-tracking data and prey-capture reports from 925 pet cats.

Most of the data came from the US, UK, Australia and New Zealand.

“Since they are fed cat food, pets kill fewer prey per day then wild predators, but their home ranges were so small that this effect on local prey ends up getting really concentrated,” says Roland Kays, lead author of the paper published in the journal Animal Conservation.

“Add to this the unnaturally high density of pet cats in some areas, and the risk to bird and small mammal populations gets even worse. We found that house cats have a two- to 10-time larger impact on wildlife than wild predators – a striking effect,” he adds. 

The researchers focused on the ecological impact of house cats – as opposed to feral cats – and enlisted hundreds of pet owners to track their feline companions, to see where they went and report on the number of dead animals they brought home. 

Inexpensive GPS tracking devices measured the distances covered by the studied house cats, which spent their days both indoors and outdoors.

“We knew cats were killing lots of animals – some estimates show that cats in North America kill from 10 to 30 billion wildlife animals per year – but we didn’t know the area in which that was happening, or how this compared with what we see in nature,” Kays says.

The researchers calculated the amount of prey killed annually by house cats and divided the number by the area in which they hunted. Some adjustments were made to the prey count as cats don’t necessarily bring all their kills home.

The study showed that house cats killed an average of 14.2– 38.9 prey per hectare per year.

It also showed that cats do much of their damage to wildlife in disturbed habitats, such as housing developments.

“Because the negative impact of cats is so local, we create a situation in which the positive aspects of wildlife – be they the songs of birds or the beneficial effects of lizards on pests – are least common where we would appreciate them most,” says study co-author Rob Dunn.

“Humans find joy in biodiversity, but we have, by letting cats go outdoors, unwittingly engineered a world in which such joys are ever harder to experience.”