Yellow pastel Bourke
Development: The yellow pastel was the first colour variety of the Bourke's Parakeet in Holland (1957). Van de Brink developed a excellent strain of this birds. Zoomer, in his book: Neophema mutations (1987) gives an account. A lot of people were breeding them and the intensity of the yellow colour got much stronger since that time. The yellow pastel is used to develop new combinations, like the pink Bourke or rose opaline-pastel, (Holland) or Lachs (Germany).
Description: The picture shows a beautiful yellow pastel cock. The head is soft rose. The eyes are bright red. The cock has a light blue frontal band. The back is yellow brown. This colour is special because of the combination of a very little remnant of brown eumelanin. The shoulder and bend of the wing are light blue. A part of the wing is yellow. Especial the tertiair wing feathers. The wing coverts are brown with a light yellow margin. The flights are light brown with a blue outer vane. The middle tail feathers are brown. The outer vane of some tail feathers is light blue. The under tail coverts are very light blue and white. The breast is light brown rose. The belly is soft rose. In this colour variety there is always a difference between cock and hen. The cock is darker. This seen clearly in the flights. The hen is more yellow. The blue frontal band is missing. After the juvenile moult the differences are clear.
Name giving: Yellow pastel. The name contains two parts: The reference colour yellow (1). This is the most marked change of colour compared with the wild type. The name that is characterising the melanin is pastel (2). The main characteristic is the reduction of the brown melanin in the whole plumage. The reduction of the eumelanin in the barbs is about 100%. In the barbules 50% of the eumelanin is preserved according to Beckmann (1973), avian genetics and member of the Technical Committee of the N.B.v.V. There is a strong reduction of melanin in the eyes and horn parts. The eyes are bright red. In the nails we see the blood vessel. The legs are flesh coloured. The beak is horn coloured. The down is white. The strong reduction of eumelanin makes that the psittacine pigments, red and yellow, are seen better in the front (rose) and the back (yellow). The reduced melanin causes less absorption of light. Also the blue colour is more clear, light sky blue. The amount of down feathers seems to be reduced. The name yellow pastel is useful to ad the colour variety to a colour series and to make difference with the rose pastel (not opaline!) which was already bred in the seventies by Besters (Holland), a friend of mine.
Name giving of the mutation factor: M-r factor. There is a substantial reduction of the eumelanin. This becomes very clear in the cross section of one of the back coverts, made by Beckmann. Only a little bit of melanin is left. Steiner speaks about a incomplete loss of melanin, due to a hypo function of the production. The reduction is equal in the whole plumage. The melanin reduction do not affect the psittacine colours red and yellow. The M-r factor is inheriting independent of the P- and S-factors. Because of the eumelanin reduction in the cortex the yellow colour is much more bright, especial in the hen. But the little remaining brown pigment gives the yellow this warm glow.