Benefits of Eradication

Islands are extinction hotspots

Extinctions on islands are more common than on continents. For example:     

  • 80-90% of all reptile extinctions have occurred on islands;
  • 80-93% of all bird extinctions have occurred on islands;
  • 50-81% of all mammal extinctions have occurred on islands.

The Pacific has more threatened bird species per unit of land than anywhere else in the world and is home to nearly 25% of the world's globally threatened bird species.

Invasive species are the biggest threat to island biodiversity

Invasive species are the major cause of the decline and extinction of native species on islands. By predating on, and out-competing native species, invasive species have been responsible for 55% of all recent bird extinctions on islands.


Causes of recent bird extinctions on Islands (ref)

Causes of recent bird extinctions on Islands (Bird Life International)

While there are many different invasive species, the two greatest threats to island biodiversity, and to seabirds in particular, are rodents and cats.

Causes of recent bird extinctions on Islands (ref) Number of globally threatened bird species affected by different types of invasive species.
(Adapted from BirdLife's World Bird Database, 2008).


A feral cat
Feral cats on Guadalupe Island, Mexico, have caused the extinction of 6 endemic bird species.
(Photo: Luciana Luna)

A mouse
House mice are competing with endemic rodents on at least 12 Mexican islands, are creating a challenging situation for their eradication.
(Photo: Araceli Samaniego-Herrera)

A rat attacking a NZ fantail nest (Photo: David Mudge) A rat attacking a NZ fantail nest
(Photo: David Mudge)


Islands are particularly vulnerable to invasive mammals, such as rodents and cats, because:

  • Native animals and plants have not evolved defences against mammalian predators.

    The isolation of islands has meant that native species have not had to compete with invasive species and so have not evolved any defence mechanisms; the native species are defenceless in the face of these new threats. For the invasive species this can mean an easy food supply.

  • Invasive mammals have no natural predators on islands.

    Unchecked by the predators and diseases that would keep numbers down in their home range, the growth of an invasive species population can be rapid once introduced onto an island.