When Darwin visited the Galápagos,
almost every island was crowded with wildlife.
Most large islands have their own species of tortoise,
which could be identified by the distinctive shape of its shell.
Today, some of these species are extinct
and on some islands the tortoises are limited to nature reserves.
The problem is people.
Settlers to the islands have brought in farm animals
and other non-native species,
which have had a devastating effect on native habitats.
The tortoises which gave the Galápagos Islands their name
have found themselves sharing their food with wild goats -
the descendents of animals brought into the Galápagos
by Ecuadorian fishermen and British pirates.
The tortoises don't have the same reach as the goats.
They're happy with handouts in the tortoise sanctuary
but find it harder to compete in the wild.
On the island of Isabela, for example,
at one stage, the goat population reached a staggering 50,000
and the National Park authorities
had to begin an eradication programme.
An eradication programme means just get out and shoot these goats.
By foot or by helicopter. Who knows? But we have to kill them
so the vegetation can have a chance to recover.
By 2002, Isabela was cleared of its goat problem.
and scientists were cautiously optimistic
that the tortoises might be able to reclaim their territory.