Birds, pests and the detailed hunting habits of Dr Flux’s cats

At his home in the hills above Lower Hutt, Dr John Flux logged 558 items his tortoiseshell cat Peng Yu left on his doorstep during her 17-year life.

Between 1988 and 2005, Peng You left about 220 dead birds at the house, plus 221 mice, 63 rats, 35 rabbits, two weasels and some lizards. Because rats climb trees and eat birds’ eggs and chicks, they are far more damaging to bird populations than ground-dwelling cats.

In 2007, Dr Flux published an account if his observations in the New Zealand Journal of Zoology, arguing that, in killing so many bird predators, his cat and probably most other domestic cats in New Zealand do more good than harm.

Flux’s paper was the most-frequently-read article in the journal’s recent history.

But not everybody was happy with the doctor’s heretical opinion – especially those who demonise cats and think the only good cat is a dead one.

The statistically minded argued that Flux should not generalise about predator-prey relations based on a sample of one cat.

Flux countered by saying his argument was based not on a sample of one cat but on a sample of 558 prey items.

With Peng You gone, another tortoiseshell cat, Tigger, took up residence with the Flux family.

They again logged all items she left on the family doorstep from 2006 to 2016.

You can compare the two cats’ diets in this month’s edition of the European Journal of Ecology.

Because Tigger ‘s life was shorter, she left fewer prey items on the doorstep than did Peng You but the ratio of birds to predators remained almost exactly the same.

Other surveys of cat diets, based on dropping analysis and watching videos of hunting cats, reveal that they consume many more rats and mice than they leave on doorsteps.

In reality, rodents and rabbits probably made up 88 per cent of Flux’s two cats’ diets, further confirming his belief that, on balance, domestic cats do more good than harm.

From a conservation point of view, removing cats from some sites has been remarkably successful, but their removal from other places has triggered unintended and disastrous consequences.

For example, because the rare native finch, the yellowhead, was disappearing from the Marlborough Sounds, an attempt was made to eliminate all predators from the area, including cats. As a result, the remaining rat population exploded. They climbed the trees, and extinguished the last of the yellow-heads in the sounds.

Another problem arose on Australia’s subantarctic Macquarie Island. There, dense populations of cats were decimating nesting seabirds, so the cats were wiped out.

With the cats gone, the island was overrun by vast numbers of rabbits. So numerous and hungry were the rabbits that they ate every blade of grass on the island and precipitated widespread damage to the nesting bird colonies.

The Australian Government had to spend $24 million ridding the island of rabbits.

Flux warns us that current government proposals to exterminate cats by 2050 could see rodents and rabbits overrun the country.