Gouldian finch

The number of Gouldian finches in the wild decreased dramatically in the 20th century due to human-caused habitat loss.[16][14] The population went from hundreds of thousands in the early 20th century to 2,500 or fewer by the 1980's.[16] The current estimated population continues to be 2,500 or fewer birds.[14] Early research suggested that a parasite called the air sac mite was responsible for the species' decline, but the mite is no longer considered a major factor.^{[citation needed]} The primary threat to wild Gouldian finch populations is an increase in extensive wildfires in the late dry season of its native habitat, which negatively impacts the availability of both tree hollows for breeding, and the seeds that comprise the bulk of the Gouldian finch's diet.[14][17] Cyclones and climate change have also negatively impacted tree hollow availability in the Northern Territory.[18]

Like other finches, the Gouldian finch is a seed eater. They eat up to 30% of their bodyweight each day.[21] During the breeding season, Gouldian finches mainly feed on ripe and half-ripe grass seeds of sorghum. During the dry season, they mainly forage on the ground for seeds. During the wet season, spinifex grass seed (Triodia sp.) is an important part of their diet. So far Gouldians have been recorded eating six different species of grass seed, but researchers have yet to find evidence of insect consumption.[22]

Newly-hatched Gouldian finch chicks

A young Gouldian finch (first day out of the nest) – note the blue nodules on the side of its beak

Gouldian finches will usually make their nests in tree hollows. They usually breed in the early part of the dry season, when there is plenty of food available.[23] When a male is courting a female, he bobs about and ruffles his feathers in an attempt to show off his bright colors. He will expand his chest and fluff out the feathers on his forehead. After mating, the female will lay a clutch of about 4–8 eggs. Both parents help brood the eggs during the daytime, and it is the female who stays on the eggs at night. When the eggs hatch, both parents care for the young. Gouldian finches leave the nest after between 19 and 23 days and are completely independent at 40 days old.[23]

Gouldian finches have brightly coloured gapes and call loudly when the parent birds return so that they are able to find and feed their mouths in the dark nest.[24]

It has been shown that female Gouldian finches from Northern Australia can control the sex of their offspring by choosing mates according to their head color. A certain amount of genetic incompatibility between black and red-headed birds can result in high mortality (up to 80%) in female offspring when birds of different head colours mate. If the female mates with a finch of different head colour, this genetic incompatibility can be addressed by over-producing sons, up to a ratio of four males to one female. This is one of the first proven instances of birds biasing the sex of their offspring to overcome genetic weaknesses.[25][26]

In the Kimberley District of Western Australia, where most wild Gouldian finch were trapped for aviculture, it was often reported as one of the more common of the eleven finch species. Until 1977, it was trapped in greater numbers than any other finch. From 1897, when finch trapping started in the Kimberley, it was the most sought after finch by trappers and the most desired by fanciers. Between the years 1934 and 1939, the Gouldian finch was the most exported single finch species. The Perth Zoo exported 22,064 finches of which 12,509 were Gouldian. Private dealers exported 35,315 finches, of which 14,504 were Gouldian. The number of finches taken in the 1958 finch trapping season was the largest for one year, of the 38,649 finches taken, 11,286 were Gouldian. The last licensed trapping of Gouldian finch in Western Australia was on 15 November 1981. In that year's finch trapping season, of the 23,450 finches taken 1,054 were Gouldian.[28] However, it is now illegal to export these birds from Australia.[29]

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  White Gouldian finch and yellow Gouldian finch mutation
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  White-breasted yellow-headed Gouldian finch (left) and black-headed male Gouldian finches
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  Adult male double factor yellow back Gouldian finch