Relationships Among Molt, Social Aggression and Disease in Gouldian Finches

Abstract

This article is adapted from a paper titled "A Relationship Between the Molt and Airsac Mite Injection in the Gouldian Finch," which the author presented to the 2009 Annual Conference of the Australian Chapter of Association of Avian Veterinarians.

Historical and Research Review

Scientific research of the Gouldian finch began in 1989 after the Northern Territory Government recognized that the wild population had rapidly declined over the previous two decades. The Gouldian finch was listed as an endangered species at this time. Research initially focused on breeding biology, population trends, disease factors, and the impact of fire on seed resources. This work revealed that the Gouldian finch relied upon a restricted seed diet and that the key wet season grasses were patchily distributed and fire, grazing and rainfall significantly affected seed production of these grasses.

More recent research examined the foraging behavior of Gouldians and the consequences of assortative breeding (i.e. a preference of Gouldian finches to select similar head colored mates). Twenty years of scientific research have now revealed significant findings but our understanding of the Gouldian finch remains limited.

Researchers have presented several possible causes for the rapid decline of the wild populations. These include commercial trapping for aviculture, habitat destruction associated with land clearance by fire and destruction of some important perennial grasses by grazing cattle, as well as feral pigs and wild buffalo. Behavioral and genetic differences between the red-headed and black-headed Gouldian finches are now being considered as an important cause of the decline. Death from airsac mite infection is also believed to be involved with declining numbers, but the exact reasons for an increased susceptibility to this infection have not been investigated.

Trapping

Trapping was vigorous for almost three decades from 1960-1988 and provided many thousands of Gouldian finches for aviculture. Although trapping had a significant effect on Gouldian numbers and populations during this time, the population should have rebounded over the ensuing 20-year period because of their prolific breeding ability. This has not occurred and at the present time numbers in remaining populations are stable but remain low. An estimated 2500 birds remain in the wild.

Habitat Destruction

Altered fire regimes have had a serious effect on the seeding grasses and nest holes available to Gouldian finches and is believed to be the single most important reason why Gouldian finch numbers have not rebounded since trapping became illegal in 1988.

The loss of traditional fire burning practices over the past 40 years appears to be responsible for the destruction of essential understory grasslands that provide wild populations with a reliable food resource. The loss of traditional knowledge occurred when cattle stations no longer employed aborigines following legislation in 1966 that gave them the right to receive equal pay as white Australian station hands. Before this time, aborigines worked for food and lodgings, and imparted their traditional knowledge of burning practices to the landowners.

Traditional fire burning practice maintains the habitat of the Gouldian finch by patch burning. Patch burns are low-heat fires, lit in the morning during the late wet season or early dry season. This traditional fire method has a positive effect on the environment. Patch burning helps regenerate several of the perennial wet season grasses (e.g. Cockatoo grass, Curly Spinifex) favored by Gouldian finches.

Non-traditional fire practices produce large hot wildfires intended to clear the land of undergrowth and native grasses, thereby allowing introduced drought resistant grasses (e.g. Buffel grass) favored by cattle to establish themselves more readily. These uncontrolled fires destroy important perennial grass tussocks and nesting habitats. However, excluding fire completely would not be beneficial, as traditional fire practices have a positive influence on the quantity of seed produced by Cockatoo and Curly Spinifex grasses.

Grazing and destruction of perennial grass plants ( Cockatoo grass and Ribbon grass) by feral pigs and buffalo have also reduced the amount of food available to Gouldian finches during the wet season, which has a negative effect on breeding outcomes.

Reduced availability of critical wet season grass seed resources is due to changes in land use and consequent changes in grazing and fire regimes. These changes when combined with natural fluctuations in seasonal rainfall are thought to be involved with the decline of the Gouldian finch in its natural environment. As yet, there are no clear links between resource scarcity and endangered status (Dostine & Franklin 2002; Fraser 2000; Crowley & Garnett 1994). In other words, starvation because oflack of food supply is not believed to be the cause of the decline in Gouldian numbers. Therefore other reasons must account for the decline in numbers.

 

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