Relationships between the Moult, Social Aggression and Disease:
Their Impact on Wild and Captive Gouldian Finches
By Dr Rob Marshall
This article is adapted from a paper entitled "A Relationship between the Moult and Airsac Mite Infection in the Gouldian Finch", which the author presented to the 2009 Annual Conference of the Australian Chapter of Association of Avian Veterinarians.
Historical & Research Review
Scientific research of the Gouldian finch begun in 1989 after the Northern Territory Government recognised 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 behaviour of Gouldians and the consequences of assortative breeding (i.e. a preference of Gouldian finches to select similar head coloured mates).
Twenty years of scientific research have now passed revealing 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, feral pigs and wild buffalo. Behavioural and genetic differences between the red and black-headed Gouldian finches are now being considered as an important cause of the decline. Death from airsac mite infection is believed to be involved with declining numbers but the exact reasons for an increased susceptibility to this infection have not been investigated.
Trapping for Aviculture
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, numbers should have rebounded over the ensuing twenty-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.
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 forty years appears to be responsible for the destruction of essential understorey 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 that uses low heat fires lit in the morning during the late wet season or early dry season.
Traditional fire methods have a positive effect on the environment and help regenerate several of the perennial wet season grasses (e.g. Cockatoo grass, Curly Spinifex) favoured 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) favoured 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.
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.
Although reduced availability of critical wet season grass seed resources due to changes in land use and consequent changes in grazing and fire regimes, combined with natural fluctuations in seasonal rainfall is thought to be involved with the decline of the Gouldian Finch in its natural environment, as yet there is no clear links between resource scarcity and its endangered status (Dostine and Franklin 2002; Fraser 2000; Crowley and Garnett 1994). In other words, starvation due to lack of food supply is not believed to be the cause of the decline in Gouldian numbers. There must therefore be other reasons for the decline in numbers.
Behavioural and Genetic Issues
Recent research by Pryke and Griffith has discovered behavioural differences between the red and black-headed Gouldian finches (Pryke & Griffith, 2009) that may account for the greater number of black-headed birds in Nature, although the red head colour is genetically dominant over black heads. It has been suggested that in the distant past the red and black headed populations were separated geographically and existed as two distinct sub-species before coming back into contact again to co-exist together as a single population. The geographic separation may also explain the distinct behavioural differences displayed by the different head colour.
Both male and female red headed birds are more aggressive than the black-headed birds. The more competitive nature of red headed birds may be explained by a limited availability of nest sites, water and food resources in the region they inhabited during their geographic separation. The passive nature of black-headed birds may reflect habitation in a plentiful and less competitive environment.
Previous research has shown that there is a higher mortality of daughters compared to sons when interbreeding between different species, subspecies or races occurs. Pryke and Griffith found that fewer Gouldian offspring survived when red headed and black-headed birds were paired together compared to when pairs of the same head colour were allowed to breed.
There are three possible head colors for wild-type Gouldian finches - red, yellow and black (Figure 1). Black headed birds comprise approximately 70 percent of the wild population although red head colour is a genetically dominant feature. High levels of male sex hormones in red headed birds suppresses immunity and predisposes them to high mortality which in the end results in greater numbers of black-headed birds even when the aggression created by testosterone gives the red heads a huge dominance advantage (i.e. allowing them to occupy the best nesting hole, be first to drink at water holes etc.) over black heads.
Head colour is also very important when Gouldians are selecting their mates. Female Gouldian finches choose their mates based on several head features including head plumage color. They prefer a mate with the same head colour. This preference has been found to be highly significant for the survival of offspring. Pryke and Griffith confirmed that genetically incompatible pairs experience a 40.2% greater mortality of sons and an 83.8% greater mortality of daughters than in broods produced from genetically compatible matched pairs (i.e. same head colours). Additionally daughters produced from mixed matings - where parents differ in head color - suffer from genetic incompatibilities between their parents that cause about 84 per cent to die young. It was also found that female Gouldian finches paired with mismatched males produced significantly more male chicks (82.1 percent), whereas females in matched pairs produced nearly equal numbers of both sexes (45.9 percent males). This series of studies revealed that female birds choose the sex of their offspring independent of genetic forces.
This new body of work reveals a behavioural and genetic incompatibility between black and red headed birds, which may provide the answer behind the failure of Gouldian populations to recover after Gouldian numbers were dramatically reduced by trapping. At this time it is likely that a greater proportion of females mated unwillingly with incompatible mates (i.e. red and black headed pairings) because of a lack of mate choice. Higher numbers of these incompatible pairs would have a negative impact on the ability of the local population to increase, due to a decreased likelihood of offspring survival and an increased number of males amongst surviving offspring (Pryke & Griffith, 2009). The end results are a decrease in females passing into the next and future generations (Pryke & Griffith, 2009).
Airsac Mite Infection
Airsac mite infections have also been thought to play a role in the decline of the Gouldian finch (Tidemann & Woinarski 1994). It has been speculated that the impact of S. tracheacolum might be exacerbated during periods of physiological stress associated with the moult and food shortages at the onset of the wet season (Lane & Goodfellow 1989 cited in O'Malley 2006a; O'Malley 2006).
Infection with airsac mite S. tracheacolum has a rapid effect on the health and survivability of captive Gouldian finches. Airsac mite infections, which often appear during the moult and breeding period in captive populations, are likely to be involved with the decline of the wild Gouldian Finch population. However, because a symbiotic relationship between Gouldian finches and airsac mites exists, any devastating effect on the wild population would require a set of circumstances that dramatically affect immunity.
In captive Gouldian finches, airsac mite infection is likely to occur when immunity is compromised during periods of overlapping stress, which are most likely to occur during the natural stress periods of moult, breeding and adolescence. For example, airsac mite infection is likely when a compressed moult is abruptly interrupted and when breeding birds and their offspring experience food shortages. Importantly, red headed birds are more likely to succumb to airsac mite infection.
Special Features of the Gouldian Moult
The time taken for the Gouldian finch to complete the moult is rapid compared to co-occurring masked and long-tail finches (Franklin et al. 1998), and thought to reflect the more mobile and dispersive nature of the Gouldian finch (Tidemann and Woinarski 1994).
Gouldian finches have adapted to an environment under control of a tropical weather system that divides the year into two seasons - a wet and dry season (Figure 2) - where they breed and moult at different times than other finches. A rapid moult appears to be an evolutionary adaptation to an unpredictable climate and tropical woodland breeding environment where the wing moult needs to be completed before the end of the dry season when seed shortages are frequent and prior to arrival of the wet season when torrential rains reduce foraging activity and curtail their ability to fly long distances in search of alternative food supplies.
A Rapid Moult
The rapid nature of the Gouldian moult has been noted by scientific researchers (Franklin et al. 1998) and is its most notable feature. Conflicting scientific reports regarding the moult in wild Gouldian finches reflect a variable rate of progress rather than any observation failing. Milton Lewis (2001) has noted both adults and juveniles moult during September, October & November with most of the wing flight feathers being replaced during October and the entire moult being completed by mid December. The moult for Australian captive Gouldians is completed most rapidly when they are housed in temperate climatic regions of Australia, have finished breeding activities by June and are provided with a perfect diet. Under these conditions the wing moult is completed late in October and the head moult by the last week in November. Under less than ideal conditions the moult period may continue until the end of December.
From Milton Lewis' research the early completion of the wing moult appears to be a significant event that guarantees strong flight by the onset of the wet season when heavy rains make foraging activities more demanding. Tidemann & Woinarski (1994) record that the wing moult period finishes November. This finding compares favourable to the time when the wing moult is completed for Gouldian finches housed in Australian aviaries. These two researchers also mention that seed shortage can occur near this time, a finding that supports a need for Gouldian finches to complete their wing moult as rapidly as possible.
For wild Gouldian finches, breeding behaviour starts as they seek out hollows late in the wet season (March and April) when a drop in humidity stimulates the germination of Sorghum grasses and the release of sex hormones that initiate breeding condition (Figure 3).
The total rainfall and extent of the wet season varies from one year to another, so that Gouldian finches are both seasonal and opportunistic breeders. During drought periods the extent of the wet season is truncated whereas during good seasons the amount of rainfall and extent of the season may be prolonged resulting in up to three clutches of eggs to be produced during a breeding season.
The amount and timing of rainfall during the wet season influences not only breeding success (Dostine et al. 2001) but also has a direct impact on the ability of Gouldian finches to complete their moult as quickly as possible. The start and extent of their breeding activity coincides with a period of peak resource availability within their habitat.
Following good wet seasons, plentiful supplies of native sorghum and other fallen seeds (Dostine & Franklin 2002; Dostine et al. 2001; Goodfellow 2005; Tidemann 1993b, 1996; Tidemann et al. 1993) provide nestlings and fledglings with a reliable food resource that remains into the moult period.
Figure 3 details the availability of several of the different grasses favoured by Gouldian finches during the breeding and moult periods.
Woinarski and Tidemann (1992) noted that the Gouldian finch is more vulnerable to drought during a moult than other co-occurring finch species because it is moulting at a time when seed shortages may occur (Figure 3). The moult is a time during which birds may experience physiological stress, as it is a highly energetic process.
The rapid moult of Gouldian finches renders them more vulnerable to the effects of stress, because there is a greater energetic cost involved with a rapid moult than a normal moult (Guillemette 2007).
Although Gouldian Finches have a more restricted diet compared to other co-occurring granivorous birds (Dostine and Franklin 2002; Fraser 2000; Crowley and Garnett 1994), the seeds of the annual grasses (e.g. Sorghum spp., Sarga spp., Vacoparis spp. Fire grass etc.) they seek and available to them for most of the moult period provide a higher quality of nutrient resource than early wet season perennial grasses such as Cockatoo grass and curly Spinifex grass.
It is thought that the critical period for physiological stress for wild Gouldian finches occurs at the end of the dry season and onset of the wet season when food supply may be very low during drought. This is a time when the flight feathers are also being replaced. The length of time food supply is scarce may vary according to the pattern of rainfall in the wet season and the dry season fire regime.
A potential to slow down or accelerate the growth of new feathers is a notable feature of the Gouldian moult that has been observed in captive but not recorded in wild birds. This adaptive feature - that is also likely to occur in Nature - allows the rate of progress of moult to increase or decrease according to the availability of nutritional resources and changing climatic conditions.
Providing additional nutrition via a soft food mix helps to accelerate the progress of the moult in captive Gouldians. The moult may also be delayed (slow down) when nutrient resources are lacking, during excessively cold or hot weather, when breeding activities extend into the moult period or by disease. In Nature, with an uncertain food supply, physiological stress in the Gouldian is avoided by its ability to accelerate or slow down the moult.
In captive birds, a compressed moult is the visible sign of an accelerating moult, whereas a delayed moult refers to a moult that is progressing slowly. The concepts of a compressed and delayed moult have not been discussed in Gouldian finches before. This paper details my understanding of a delayed and compressed moult in Gouldian finches, their relationship to each other and disease with possible links to the decline of wild populations.
The Moult in Captive Gouldian Finches
The moult of captive Gouldian finches is an annual seasonal event with a starting time that may vary slightly depending upon local climatic conditions. In Australia captive Gouldian finches may start to moult as early as July. Across the Northern Hemisphere the moult should start in January (Figure 4). A loss of the first (most proximal) primary flight feather heralds the start of the moult period; an occasion that often goes unnoticed because no other feathers are moulted and very few feathers are noticed on the aviary floor. The moult progresses slowly at this stage with a single primary flight feather of each wing being replaced gradually over a period of several weeks until after the fourth primary flight feather is dropped. At this time the secondary flight feathers start to moult (Photo 2).
Photo 2 Four new primary flights feathers are seen in this wing. No secondary flights have been moulted yet.
Captive Gouldian finches carry between nine and ten primary flight feathers. They follow the same moult sequence as for wild populations with the first four primary flight feathers of each wing being replaced one at a time and in sequence (Photo 2). The main wing moult period begins in August following the re-growth of the fourth primary flight feather on each wing and ends late October. Normally, during this time each primary and a corresponding secondary flight feather of each wing are replaced in sequence and one at a time. The body moult is less critical for survival than the wing moult and is heaviest during September and October. The head feathers are the last to be replaced. These are moulted during the last weeks of November and first week of December. Sometimes pinfeathers appear on the head (Photo 3).
Photo 3 Pin feathers on the head may occur in some birds towards the end of the moult period. This may be a healthy or
The speed of the moult may accelerate or slow down at any stage in captive Gouldian finches. It is the primary flight feathers that best reveal a change in pace of the moult.
The start time of the moult in captive flocks exposed to natural sunlight conditions may vary slightly according to geographical location and local weather conditions. However under ideal conditions, captive Gouldian finches in Australia start to moult their primary flight feathers in July. February is the equivalent month in the Northern Hemisphere.
This initial stage of the moult often goes unnoticed as the four proximal primary flight feathers are replaced one at a time. The replacement of these four feathers is gradual and takes over a month to complete. Consequently there is no undue energetic or nutritional burden on the bird and physiological stress is minimised. However, the early progress of the moult may be retarded by poor nutrition, disease, breeding activity or cold winter weather conditions that often persist throughout July and August in temperate parts of Australia and in New Zealand.
In order to avoid a delay in the progress of the starting phase of the moult, captive Gouldian finches should not be allowed to breed beyond June in the Southern Hemisphere. In the Northern Hemisphere all breeding activity should cease by January.
Most Australian Gouldian breeders and scientific researchers view September as the beginning time of the moult period. However, this is incorrect as the moult begins at least a month beforehand. Instead September is the time when the peak phase of the moult begins, being obvious to fanciers as many feathers appear on the floor of the aviary. At this time, both primary and secondary flights start being replaced and new feathers on the body of juveniles appear. This is a time of increasing physiological stress and vulnerability for the Gouldian finch, as there is a sudden increase in energetic and nutrient requirements.
When the moult is progressing as rapidly as possible, the wing moult is complete by mid October. As with wild birds, there is variation with some individuals taking longer to complete their moult (Milton Lewis, 2001).
Individuals born at the beginning of the breeding season start to replace their primary flight feathers within a month of fledging. This occasion also goes unnoticed by breeders, as the wing moult progresses very slowly and juvenile body colour remains unchanged until August/September.
Under ideal conditions the moult of adult birds begins as early as July. By the first week of August three or four primary flight feathers have been replaced in both adult and juvenile birds. Juveniles bred early in the breeding season start the body moult (i.e. replace their body contour feathers) by the second week of August. Adult birds start to drop body contour feathers during the second half of August.
Under normal conditions, each primary flight feather is replaced one at a time in an orderly sequence starting from the innermost (proximal) and ending with the outermost (most distal) primary flight feather. The body feathers and secondary flight feathers start to moult when the fourth primary flight has been replaced.
This marks the beginning of the peak period for the wing moult that continues throughout September and into October. Sometimes two or more adjacent new primary flight feathers may be seen growing simultaneously during the peak period of the moult. All wing flight feathers are replaced by mid October. The head feathers start to be replaced towards the end of the wing moult. The moult is concluded during the first weeks of December (Photo 4).
Photo 4 This photo taken on December 5th in Australia shows the head moult is almost complete in this healthy orange
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Alan Simpson's soft food recipe uses hard boiled eggs, breeding crumbles, and Dr Rob Marshall's health supplements to produce excellent breeding outcomes.