Mick Everett from AG WEST fits a feral donkey
with a tracking collar in the Kimberley
Photo: Andrew Johnson, AG West
Wild donkeys, horses, cattle and, in the drier areas, camels,
are all avid grazers in the tropical savannas. They can compete
with native herbivores and also with stock for forage and water
(although camels are probably less competition than horses and
Feral donkeys in Western Australia are the descendants of pack
and draft animals used in the development of the Kimberley area in
the late 19th century. In central and northern Australia there is
an estimated 300,000 feral horses. To see a recent list of research
findings on feral donkeys click here .
Because of the selective nature of their grazing, for this can
change the composition of plant species in an area. Donkeys and
horses prefer certain plant species, and their heavy grazing on
these species allows other plants — less palatable both
to the ferals and to native animals — to proliferate.
Eventually, large areas can become virtual monocultures.
This has effects throughout the ecosystem. Many native species,
especially birds, rely on plant products for food. A diversity of
plant species, setting seed at different times of the year, ensures
a continuous food supply. But if only one or a few species remain,
then seed or fruit may be abundant only at one time of the year,
leaving the area virtually food-free the rest of the time. This
simplification of the species richness in the region's plant cover
is ecologists' main worry about feral grazers in the savannas.
In addition, the heavy hooves of these animals can cause soil
erosion, especially if many animals are gathered in one area, such
as happens around water sources in times of drought.