Case study blue mutation


My first blue opaline Bourke's parakeet was born in 1997. I was breeding the different colour varieties of the Bourke's during thirty years but this blue Bourke's is to me the most intriguing colour variety. Two blue hens and one cock split for blue were born in my aviary from a pair rose opaline Bourke's without extra blue. I was busy to develop a strain of good format and breeding qualities of this beautiful new and unexpected colour variety for several years . I used in the first years not-related wildtype Bourke’s for mating. Breeding results proved a recessive inheritance.

Expectation: Most bird fanciers expected that a real blue Bourke's was not possible because the wildtype Bourke’s parakeet has no green plumage, not a single feather in the whole plumage. And so did I. The biggest part of the plumage of the Bourke's, the neck, the back, part of the wings and tail is missing feathers with a blue structure. In all known blue colour varieties of parrots the blue colour is caused by a total loss of the red and yellow pigments. Green becomes blue. This mutation of the psittacine formation is not turned up in the Bourke's till now. And the expectation is that when it does appear, the result shall be a Bourke's that is even more brown coloured then the wild type. This is the reason that a real blue Bourke's was not expected and seemed to be an impossibility.

Surprise: It was a real surprise to see this different colour variety for the first time. A soft coloured, sky blue Bourke's with a grey head and dark flights with blue margined wing coverts. It was more than I expected from a brown Bourke's. The picture shows clearly the differences between first blue hen (1997) and her rose opaline father.

first blue Bourke

Modification or mutation? A modification is caused by disease, diet or other environmental influences. A modification does not inherits. I am breeding this colour variety during six years and build up a strain. That is impossible in case of a modification.

Blue factor? The name blue factor is misleading. I studied the inheritance of this so called blue factor of the parrots. Most documentation is concerning the mutations of the budgerigar. Blue is a loss-mutation. When there is a total loss of red and yellow pigments in the plumage the remaining colouring elements, the eumelanin and blue structure are colouring the birds blue. Green birds became blue but not a yellow bird like the cockatiel. He is missing the blue structure in the feathers.
Why should we call this factor blue factor? I tried to solve this puzzle about the name giving. I found the solution in the authoritative work of Taylor: “Genetics for budgerigar breeders”, 1961, page 7. He introduced the name blue factor. He himself was aware of this problematic name giving. He wrote that “an absence of yellow” factor was a better name but he choose the name blue factor ”as a matter of convenience”. I learned that ideas about the inheritance of the blue budgerigar and the blue splendid are useless to understand the inheritance of the blue Bourke's. But I am also sure that this incorrect name giving can hinder the understanding of the Bourke’s mutations. The same so called blue factor gives in the Bourke's an equal coloured brown Bourke's. This name blue factor is misleading.

Side effect of the opaline? Is the appearance of the blue Bourke a side effect of the same eumelanin mutation factor that caused the opaline characteristics? This idea can stem from the fact that this mutation factor appeared in the rose opaline Bourke's first. There are different reasons to show that this is not the case.

1.There is a different heritage. The opaline colour variety is the result of factor with a sex-linked heritage. The inheriting of the blue Bourke's is recessive.

2. If it is the same mutation factor that causes the blue back, wings, rump and tail it has to be questioned why this blue colour variety did not appear thirty years ago?

3. The development of the opaline makes the blue colour disappears. We observe this on the shoulder, some parts of the flights, the tail and parts of the under wing. Some examples: The blue frontal band of the rose opaline cock disappears. On the shoulder the blue disappears. The bent of the wing has less blue. A broad under wing stripe appears. The coverts of the wing are losing blue. The tail of the rose opaline is grey or rose. In summary blue disappears from the plumage.

In the blue Bourke's the development is opposite is . The blue colour is extended in the head, the wings, the shoulder, the flanks and tail. The colour of the down can be dark, not white. Sometimes the blue Bourke's has a grey and blue front. The hen can have a blue frontal band. Nobody could expect such a blue specimen in the opaline series. This cannot be attributed to the same factor that created the opaline.

4. The down of the opaline is white, the down of the blue Bourke is dark.

5. The extension of the blue structure is not restricted to the opaline. I bred a light blue pastel beautiful blue back and yellow brown wings. A wonderful combination of colours. Some wildtypes in my strain have more blue then normal. The margins of the wing coverts are blue or green. On the breast, the hind neck and the back there is a blue or green suffusion. In the yellow back pied (spangle) I saw specimen with a green hind neck.

This makes clear that the mutation factor can combined with other mutation factors, like the cinnamon, the fallow, the pastel and the dark factors. When a total loss of eumelanin takes place the blue structure can not express himself.

The conclusion is that the new factor can not be a side effect of the opaline. The mutation factor inherits independent of the M-mutation factors.

Explanation: I found the solution of my quest for the cause of the blue colour variety in the description of the feather structure of the wildtype Bourke's and some colour varieties. In 1973, Beckmann, a Dutch inspector and writer about bird breeding and genetics, completed a “Standaard Neophema” by order of the Technical Commission of the N.B.v.V. ( “Nederlandse Bond van Vogelverenigingen” ) in Holland. Beckmann was studying the micro structure of the feathers of the wildtype of the Neophema and the Bourke's. He makes difference between feathers without blue structure (feathers of the common type) and feathers with a blue structure (feathers of the structural type). When I red the careful description of the feathers of the Bourke's I found the answer on my questions. The wildtype Bourke's has feathers of the common type in the hind neck, the back, part of the wings and tail. Without blue structure. This helped me to understand the effect of the new mutation.
The factor that caused the blue Bourke's has to be a structure factor (S-factor). This factor controls the feather construction. The gene works in the zone of differentiation under the follicle. The altered gene causes a change from feather of the common type in feather of a structural type. Barbs with a blue structure and grouping of the melanin in the centre. This is the reason that new blue coloured feather fields are developing. This factor should have been called blue factor. To prevent confusion I named this factor structure factor (S-s factor, s=structural change).
It is not possible that this is written on the account of the mutation factor (M-factor) of the opaline.
This is another factor than the P-factor that causes the blue budgerigar and the white fronted blue splendid. This mutation factor is very special and gives the possibility to develop total new colour varieties. It is a winn-mutation not a loss-mutation in the terminology of Steiner.
Thus far I bred the blue opaline (B-5), blue pastel (B3), blue opaline-pastel (B53) green opaline (G5) and green opaline pastel (G-53).

Some blue and green Bourke's

Conclusions:
1. The blue Bourke's is the result of a mutation not a modification.
2. The cause is not a mutation that gives a total loss of psittacine colours (P-factor).
3. It is not a result of the mutation factor (M-factor) of the opaline.
4. The only possible explanation is that the gene that controlled the formation of the feather structure is altered by mutation. A replacement of feathers of the normal type by feathers of the structural type takes place. The mutation factor is a structure factor (S-factor). The results are several new blue feather fields: the head, upper and lower back, part of the wings and the tail.
5. This mutation factor inherits recessive and inherits independent of the mutation factor of the eumelanin (M-factors).

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Copyright 2003 by Bob Fregeres

E-mail: fregeres@bourkes-parakeet.nl

12/24/03