From Tropical Topics newsletter, No. 73 May
2002, produced by Stella Martin at the Queensland Environmental
Protection Agency. Download the PDF to read the whole issue.
Partridge pigeon Photo: Fiona Fraser
Partridge pigeons feed on the seeds of more than 60 plant
species. They are found at the top of the Northern Territory, where
birds have bright red skin around the eyes, and the Kimberley where
a distinct sub-species has bright yellow skin around the eyes.
Although able to fly, these birds opt to walk. Outside the breeding
season they gather in groups of 30 or more, cooing softly as they
trot together between waterholes and feeding grounds. If the grass
is too dense, they will choose to travel along tracks. When
disturbed the birds initially freeze, only at the last minute
bursting up in flight with swift, noisy wingbeats in a manner
reminiscent of partridges.
These birds are sharing the problems of other seed-eating birds
in the savannas, having suffered a decline in the last century and
become extinct in many parts of their previous range. Their
ground-nesting habits have probably left them vulnerable to
introduced predators but research indicates that grazing and
changed fire regimes have also had a negative effect on these
birds. To see a recent list of research findings on the partridge
click here .
Pied imperial-pigeon (also known as a Torres Strait pigeon. Photo:
Martin Armstrong ©
n October 1996, a pied imperial-pigeon was captured in a small
patch of rainforest in the Northern Territory where it had landed
to feed on fruit. This particular pigeon was then tracked for 78
days. In that time it travelled 65.5 km,moving from one rainforest
patch to another. At each of the numerous sites it visited,
researchers estimated it deposited between 10 and 20 seeds in its
droppings, many of them having been transported from the previous
patch of forest.
Pied imperial-pigeons (also known as Torres Strait pigeons)
migrate from New Guinea to northern Australia each summer to breed,
and rely on a steady supply of fruit from rainforest trees to
sustain them. In the Wet Tropics, rainforest occupies a fairly
continuous strip, but in the savanna regions it occurs in patches
where local conditions provide sufficient moisture. Averaging just
3.6 hectares in size, a total of about 15,000 of these patches in
the Northern Territory amount to just 0.2 percent of the land.
Nevertheless, these little areas are vital for a
suite of fruit eating birds such as pied imperial-pigeons,
rose-crowned fruit-doves, figbirds, yellow orioles, common koels
and great bowerbirds as well as flying foxes. But, just as the
animals need the forest patches, so the forest patches need the
animals. They are essential dispersers for plant seeds, with an
average patch receiving an estimated 190 seeds a day from their
avian visitors. Researchers predict that the loss of too many
patches would lead to a food shortage — and the consequent
loss of these dispersers. The loss of dispersers would, in turn,
lead to a gradual decline in biodiversity and, eventually, the loss
of remaining patches.
This would be likely to have consequences elsewhere
also. When rainforest fruit is scarce, the fruit-eaters move into
surrounding habitats and probably play a dispersal role here too.
Each patch of forest may seem insignificant, but together they play
a vital role in maintaining the network of interdependence which
keeps the ecosystem functioning. To see a recent list of research
findings on the pied imperial-pigeon
click here .