330 ISLAND REMEDIES: THE CONSERVATION OF ISLAND ECOSYSTEMS
Box 12.2 The arrival and eventual removal of ecosystem transformers: feral goats and
Judas goats
Goats in the Canaries
Introduced from North Africa in the first
millenniumBCby the Guanches, goats (Capra
hircus) enjoyed a feral status on all of the Canary
Islands until just a few decades ago. Today herds
of semi-wild goats roam freely only on
Fuerteventura. With the exception of the now
extinct giant tortoises (Geochelone burchardiiand
G. tamaranae), the Canarian flora evolved without
large grazers for several million years, and thus
generally lacked the defensive spines and toxic
compounds typical of continental flora. The long
history of goat grazing has thus undoubtedly
been hugely significant in transforming the
vegetation cover of the islands, and most likely in
reducing native endemic species to extinction. It is
difficult to be certain how many species
populations were lost in the absence of fossil
data, but it is clear that goats and other
introduced herbivores have been directly
responsible for reducing some persisting endemics
to the very brink of final extinction (e.g.
Marrero-Gómezet al. 2003), just as also occurred
for example on St Helena (Cronk 1989).
Following the declaration of the summit region
of Tenerife as a National Park in 1954, goats were
removed from the uplands. After the shift of the
economic development model from agriculture to
mass tourism during the 1960s, the goats slowly
began to disappear from the rest of the Canarian
landscape. Finally, in 1980, the last wild goats
were successfully extirpated from the uninhabited
10 km^2 island of Alegranza, marking the end
(except on Fuerteventura) of an influence that
lasted for more than two millennia. In response to
the removal of the goats, in those areas escaping
development, a trend of vegetation recovery can
be seen. In the extreme (arid) climates of the high
uplands this has not been a particularly rapid
process, but nonetheless, several rare plant
species have since greatly increased in abundance
(e.g. the endemic Pterocephalus lasiospermus).
Conservation efforts have focused on assessing
the key life-history phases and autoecological
(e.g. germination) requirements of highly
threatened plant species. Breeding programmeshave been established and efforts are being made
to reintroduce populations into the wild. This
approach requires a good and sustained level of
funding, alongside the availability of suitably
trained scientists, appropriate infrastructure, and
finely tuned management plans for protected
areas (e.g. see Marrero-Gómezet al. 2003).Removal of feral mammals
Goats have been introduced on numerous islands
around the world, sometimes to provide a food
resource on uninhabited islands for visiting sailors,
other times by settlers. They are highly effective
ecosystem transformers, and present huge
conservation problems in many islands. However,
they have now been eradicated successfully from
over 120 islands across the world (Campbell and
Donlan 2005). Whereas in the past, such campaigns
typically took many years to complete and often
struggled to eradicate the population altogether,
modern technology has now been harnessed to
enable swift and effective eradication of populations
of goats numbering many thousands.
An illustration is the use of so-called Judas goats.
Animals are trapped and radio-collared before
being re-released, upon which (being social
animals) they typically find and remain with other
goats. They are then tracked and the other animals
accompanying the Judas goat are shot with high-
powered rifles. The Judas goat is then released
again, and the process repeated. This approach
allows the last members of the feral population to
be tracked down and eliminated. Similarly, feral
pigs, which were causing huge ecological impacts
on Santiago island in the Galápagos, were finally
eliminated from the island at the end of a 30 year
campaign, during which some 18 000 animals
were killed (Cruz et al. 2005), with many lessons
learnt towards increasing eradication efficiency in
future efforts.
Although some environmentalists raise
principled objections to such culling programmes,
there is no doubting their central importance in
protecting the native biota of many oceanic
islands (Desender et al. 1999, Campbell and
Donlan 2005, Cruz et al. 2005).