Gouldian Finch Recovery Project
Theory
The decline of gouldians has occurred throughout the specie's distribution. This is a significant observation because it suggests that the cause for the decline has also occurred throughout the same distribution suggesting that a major event has influenced the success of the entire species. Previous research had suggested that the dry season did not appear to pose environmental hardships for the gouldian finch.
Gouldians reproduced freely, had abundant stocks of sorghum seed and water. However the wet season may be a difficult period. We have found that there are periods of low seed availability between the first heavy rains and the first seed produced by perennial grasses.
That same period is also the time when gouldians moult into a completely new compliment of body feathers, unlike any other finch species in the region. Also supporting this is evidence showing that unlike other species of finch living within the same locality, gouldians do not increase their body condition during the wet season. These observations suggest that the wet season ecology of the gouldian finch may hold the key to understanding the cause for the decline.
|
| Analysis of body condition in finches throughout the year indicates that species such as masked finch (black triangles) and long-tailed finch (yellow circles) increase their body mass during the wet season. Gouldians (red diamonds), however do not display significant increases in body mass. This absence of seasonal conditioning may have direct consequences resulting in lower survival during the next dry season and lower reproductive output. |
|
In the past it has been suggested that causes for the gouldian finch decline may have been as a result of large scale commercial trapping for the pet industry or because of the air-sac mite Sternostoma tracheacolum. It may also be that mites and trapping have only added to the problem. Legal harvesting of gouldian finches ceased more that 20 years ago yet the species still declines.
Large-scale trapping may have increased the rate of a decline that was already occurring. The appearance and apparent increase in the number of sick birds suffering from air-sac mite infection may well be because gouldians are low in immunity as a result of some other major event such as starvation.
This has led to the following theory:
Environmental Change |
 Lower food availability |
|
Poor Health |
|
Disease |
The next important question is to ask what sort of environmental change or changes could occur over such a vast area that results in significant reductions of seed yield.
There are a variety of factors that appear to have the potential to influence the seed yield of native grasses. Current research suggests that the two most important of these are grazing animals and fires. Grazing animals, particularly feral pest species such as horses and pigs destroy large tracks of wet season gouldian feeding areas. The destruction is caused in two ways, firstly by pigs digging up perennial tussocks and eating the roots and secondly by horses eating both the leaves and immature seed stems before seed has been set.
|
Fire also appears to play a major role in determining the yield of seed plants are able to produce, however this is far more complicated and difficult to observe because the effects may not be apparent for several years.
Firstly fires may directly reduce the number of surviving plants and plant species within an area. This does not necessarily occur in the first year but may be a gradual process where the nutrient reserves held by the plant are continually used as a result of successive annual burns.
Eventually these reserves are depleted to a point where the plant dies. Unfortunately while these nutrient reserves are being used the plant is also producing less and less seed.
Less seed and gouldians as well as other finches starve. Secondly, annual burning over many years can reduce the available nitrogen in the soil, which could reduce the seed yield. It has also now been observed that some grass species such as soft spinifex do not set seed the year after a fire. Again the result is no food for the gouldians.
|
Regrowth of soft spinifex a year after burning and lacking seed stems. Importantly note the lack of seed stems. |
|
Healthy, seeding spinifex two years after burning. Note the abundance of seed stems that contain essential resources for gouldian finch survival. |
f course this is only a brief outline of where our research is pointing, but we are now investigating the full potential of the role fire plays in shaping the ecology of northern Australia, especially with regard to the gouldian finch. Some of our present research is experimentally manipulating nutrients, fire and grazing on plants in both field trials and in shade houses.
At the same time we are monitoring the success of different gouldian populations living with different fire regimes. We have also begun an extensive program of protective fencing to save crucial areas of grassland from pig and horse damage.
