Plight of pigeons

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 pigeons

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 pigeon click here .

Flying tree-planters

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 .