Removing cats won't save our birds

BOB BROCKIE - WORLD OF SCIENCE
Last updated 07:34 04/02/2013
ENEMY WITHIN: Beware of the cat.
REUTERS
ENEMY WITHIN: Beware of the cat.

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OPINION: Gareth Morgan wants to rid the country of cats because they kill our bird - this sounds reasonable but New Zealand scientists have evidence to show this would be futile and dangerous.

Unknown to most people, three acclaimed world experts on animal predator/prey relationships live, or lived in the Hutt Valley - Mike Fitzgerald, John Flux and the late John Gibb - all former population biologists in the now-defunct Department of Scientific and Industrial Research.

These scientists spent decades investigating feral cats, rats and rabbits in the Rimutaka bush, suburban Melling and on Wairarapa farmland and none would agree with Dr Morgan's views.

Setting thousands of traps, Dr Fitzgerald calculated the number of cats and rats in the Orongorongo Valley for 23 years. The cats held the rat numbers in check for years but when cat numbers fell, the rat population shot up. The cats also held the riverbed rabbits in check and their population also shot up when the cats disappeared.

Dr Flux logged everything his cat Peng You brought to his Melling house for 17 years. The cat brought home 558 little victims which included 53 native birds (mainly silvereyes) and 151 foreign birds (such as blackbirds and sparrows). Peng You never killed tui or New Zealand pigeons. Indeed, these species established themselves on the Melling property during his time there. More to the point, Peng You killed 63 rats, 221 mice, 35 rabbits, and two weasels during his 17-year lifetime. Rats and weasels are much more effective predators than ground-based cats as they climb trees to eat birds' eggs and chicks in the nest and also eat the flowers, fruit, berries and seed before the birds can eat them.

Following Peng You's demise, rabbit numbers shot up round the Melling property. On balance, Dr Flux thinks his cat, and probably other suburban cats, actually benefited native bird populations by killing so many of their more numerous predators. Forest & Birders argue that this is heresy and claimed that he could not argue from a sample of one cat. Dr Flux counters that his was a sample, not of one anything, but of 558 prey items.

In a two-year trial in the Wairarapa in the 1960s, Dr Gibb showed that cats were more effective than pest destruction boards in controlling rabbits. To prove his point, Dr Gibb persuaded the board to stop shooting rabbits on 1200 hectares of hill pasture and scrub for three years. At the end of that time there were fewer rabbits there than on the adjacent shot-over land.

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Our scientists proved that, if we get rid of cats, other predators such as fast-breeding rats, stoats, weasels and ferrets will fill the ecological gap. Their take-home message is that if we want to save our birds we must eliminate the whole "suite of predators". This has happened on Kapiti, Little Barrier and Tiritiri Islands, the Karori Sanctuary and other "mainland islands".

Only on these cat- and other predator-free islands do native birds, bats, lizards and insects really flourish.

Oops! Our cat has just brought in a baby rabbit.

- The Dominion Post

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