Scientific American - USA (2022-02)

ADVANCES

12 Scientific American, February 2022 Graphic by Katie Peek

10 hectares

165 islands

100 hectares

55 islands

1,000 hectares

22 islands

100,000 hectares

1 island

10,000 hectares

7 islands

5 hectares

77 islands

1960 2020

Islands, by area Islands with extant pests (93) Islands cleared of pests (115) Islands never invaded (114)

Auckland

Wellington

SOUTH ISLAND

(TE WAIPOUNAMU)

15 million hectares

Christchurch

Dunedin

Black squares

compare

island areas.

Each line

represents

one island.

For each island,

dots tally the

status of each

pest species.

Black rings mark

failed eradication

attempts.

Stewart Island

(Rakiura)

Empty circles mark

where a species

was removed.

The Ambitious Kiwi Quest

New Zealand has successfully cleared

a third of its smaller islands of invasive

species ( dots ). But the main islands present

a much larger—and perhaps insur ­

mountable—challenge. They account for

97 percent of New Zealand’s land area and

contain two major cities, Auckland and

Christchurch, where rat eradication

will be difficult.

How

It’s Going

Despite enthusiasm for the

predator­free program, rat

populations are growing. In 2019

New Zealand beech trees had a

mega mast—like a superbloom for

beechnuts—and both rat

numbers and rat waistlines

ballooned.

Capital Success

In 1990 the first fenced

urban wildlife sanctuary opened

in a Wellington suburb. The

sanctuary, called Zealandia, now

attracts nearly 150,

visitors a year.

TARGET SPECIES

Norway rats

Native to China, Norway rats are

ground hunters that can swim up

to a mile between islands.

Ship rats (black rats)

Smaller than Norway rats, ship

rats hunt both on the ground and

in treetops, but they’re not as

strong swimmers.

Polynesian rats

Also called kiore, these small

rats served as a food source for

Polynesian explorers.

Stoats

Members of the weasel family,

stoats are agile hunters. They’re

also strong swimmers, making

island reinvasion a concern.

Australian possums

Brushtail possums were introduced

from Australia in 1837 because

they were (and remain) a source

of fur. But they also eat bird eggs.

MAINLAND EFFORTS

Ground-based poisons

Cereals laden with vertebrate

pesticides, distributed by hand.

Aerial poisons

Pesticides released from buckets

underneath helicopters.

Traps

Baited boxes with kill mecha­

nisms that dispatch pests.

Fenced areas

Cleared zones with

barriers to prevent

pest reentry.

NORTH ISLAND

(TE IKA A MAUI)�

11 million hectares

Gray means

no data

are available.