The Greywing budgerigar mutation is one of approximately 30 mutations affecting the colour of budgerigars. It is the underlying mutation of the Greywing variety. When combined with the Clearwing mutation the variety is known as a Full-bodied Greywing.
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Appearance
The body colour of the Greywing variety is about half the intensity of the corresponding normal variety, and the wing, head and neck markings are similarly reduced in intensity from black to mid-grey. The spots are grey and the cheek patches are pale violet. The tail feathers are grey with a bluish tinge. The overall effect is a very pleasing combination of pastel shades, particularly so in the blue series.
In comparison to other varieties, the grey markings on a Greywing are of a similar intensity to the brown markings on a Cinnamon, maybe a little deeper, and considerably deeper than those on any Clearwing or Dilute. The body colour is deeper than most Dilutes, yet much paler than the body colour of Clearwings.
As with Dilutes and Clearwings, there is considerable variation in the depth of body colour and wing markings of Greywings. Greywings at the paler end of the range correspond with the World Budgerigar Organisation's standard of 50% of the intensity of normal colouring, while those at the darker end approach the depth of colour of normals. Greywings which are split for Dilute are often slightly paler than pure Greywings.
When pure-breeding (homozygous) Greywings are paired with pure-breeding Clearwings the resulting offspring, known as Full-bodied Greywings, are quite distinct in appearance from both parents. They have a body colour almost as deep as the corresponding normal variety and with the rich sheen of the Clearwing, but with medium grey markings marginally darker than the parent Greywing. The tail and flight feathers are like the parent Greywing, but the cheek patches are violet, almost as dark as those of the corresponding normal.
Genetics
The Greywing is an autosomal mutation of the dil locus with the symbol dilgw, and so is a member of the multiple allelic series which also includes the Dilute (dild) and Clearwing (dilcw) mutations. The Greywing allele is recessive to the wild-type, dominant over the Dilute allele and co-dominant with the Clearwing allele.
The effect of the Greywing mutation is fully visible only in a bird which is homozygous for the Greywing allele with the genotype dilgw/dilgw or is heterozygous with the Dilute allele, with genotype dilgw/dild. The effect is to reduce the number of melanin granules in both the cortical and medullary cells of feather barbs over the whole body by around 50%.
When heterozygous with the wild-type allele with the genotype dil+/dilgw the phenotype is identical to the wild-type Light Green and the bird is known as a Greywing/dilute.
When the Clearwing and Greywing alleles are both present the genotype is dilcw/dilgw and the bird is known as a Full-bodied Greywing. Both alleles are partially expressed, giving the bird wings like a Greywing and a body coloured like a Clearwing. A fuller description is given under Appearance above.