Case study edged

Description

The first gezoomde (edged) Bourke was bred by Beurskens (Holland) in 1976. (see the double picture below). It is a good sized cock . He has a mixed yellow and red wing, back and rump. The tail is grey white. The eumelanin is gone in this areas almost. The tips of the wing feathers and wing coverts are dark. Most of the blue colour disappeared because of the lack of melanin. The shoulder is showing some blue. The tail feathers are grey white with dark tips. The under tail coverts are white. The head is dark. The eyes are black.

Development

Beurskens bred this new variety from a pair of two wildtype Bourke that were not related. When Beurskens brought his hobby to an end I was happy to buy some of his edged Bourke's . The old cock born in 1967 I wanted to get because I could form a good opinion about the new colour variety. I got also a yellow edged hen born in 1976. The wings and back of this bird did not showed red pigment. Further I could buy some splits. A part of the notes he made about breeding this birds I got also.

When I collected my birds with a rented car I had an accident on a crossing. A bad omen? The side of the care was damaged, but I could reach home. The boot where I transported my birds was OK There were no difficulties with my birds. On the base of the notes Beurskens gave me I could reconstruct the descend from my Bourke's.

Descent

Abbreviations: 0X and 0Y are not related Bourke's. The other Bourke's represented by a year and number were bred by Beurskens.

Grandparents: Breeding pair: 1961-016 x 1962 0X. Both were not related wildtype Bourke's. The cock he bred himself, the hen he did buy in his neighbourhood.

Parents: 1964-07 x 1963-0Y. This pair was not related also. The cock was own breed. The hen was bought.

Edged cock: 1967-24. The first "gezoomde" was a cock.

Edged hen: The edged cock was mated with 1966-04, a wildtype hen. The hen was born from the same grandparents. She was related. From this pair a wildtype cock was born 1969-06. This cock was mated to 1968-11. This hen was born from the same parents of the edged cock. This pair brought an edged hen 1976-01.

The first fourteen year of breeding only a few edged Bourke's were born. The loss of the eumelanin turned out to be very variable. There are edged with little eumelanin but there are edged with a lot of eumelanin left also. There are specimen that look alike the wildtype. You have to discover the markings on the primaries. A pattern of very fine grey striping , remnant of melanin in the barbs of the feathers is one of the characteristics of the melanin.

My first experiences come from two periods. In the beginning I had no luck with this birds. The Bourke's were breeding inside for many years. I acquired them in summer I housed them in aviaries in the open. They could go inside in the shed if they want. The two edged proved to be delicate. The cock was to old. I bought him to have a proper idea about the mutation. The hen died without offspring. The splits gave me no edged. In 1984 I sold the last pair to Paters. He was more lucky than I was. From this pair edged were born. After some years I tried again with edged get from him. In this second period I had results and get to know the different varieties of the edged.


Mutation factor

Out of all the facts about the descent some important conclusions can be drawn.

1. It was not a modification. The characteristics are the same in the different varieties, the dark tips on the flights, the fine stripes in the primaries, the black eyes and the dark head.

2. The first edged was a cock. It is not a sex-linked inheritance.

3. In 1976 an edged hen was born from two wildtype parents. A dominant inheritance is not possible because a new identical mutation is out of the question.

4. The inheritance is recessive.

5. The mutation factor (M-factor) is inheriting independently from the psittacine pigment factors (P-factors) The first edged cock had a red and yellow back. The first hen was yellow like a lemon.

Some other characteristics:

6. More cocks are raised then hens. Four cocks in proportion to one hen.

7. Less edged are bred than could be expected from a recessive inheritance. This forms an argument for a multiple mutation factor.

Name giving of the mutation factor: The cause of the new colour variety is the distortion of the production and deposition of melanin grains. Van Eerd was suggesting in one of his lectures that in the beginning of the formation process to much eumelanin is produced. More then can be transported. The production cells burst and afterwards no eumelanin is deposed in the feather. When this takes place early in the process only the feather tips contain eumelanin. When it happens later a weak edged specimen appears.

The mutation factor is a M-factor. Because the production and deposition suddenly is interrupted a proper name is M-i factor (i means interruption)


Colour variety

Spangle is not a proper name for this colour variety. In the beginning this name was used by breeders who were thinking that it was the same mutation as the spangle budgerigar. The mutation factor of the spangle is dominant inheriting. This name does not suits. And there is no inversion of the melanin in the wing coverts.

The wing coverts on the picture are showing very clear the differences with the spangle colour variety of the budgerigar. There is no inversion of the melanin in the margins. In the wildtype Bourke the margins are lighter then the feather himself. In the picture of the edged Bourke we see a very little pigmentation of the margin but no dark edge. Most of the remnant of melanin we find in the centre of the feather. There is no inversion. The whole feather shows a loss of melanin.

Melanin pattern. When we compare the wing of the wildtype with the wing of the edged we see the loss of melanin. The tips of the primaries are dark. The primaries are grey. Not all melanin is lost. We see some melanin in the shaft of the feathers. Also in the barbs we see a trace of melanin. This is very characteristic, a basic pattern, not seen in other M-mutations. We find by careful inspection in birds with a minimal loss of melanin this pattern also. Summarising: In strong edged Bourke we find dark tips. In less edged Bourke we find the fine stripes in the feathers of the wings.

This picture shows a cock with a nice pattern, the tips of the wing feathers and the greater wing coverts are dark. Also the shafts of the feathers have some melanin. Together this forms a pattern. This pied pattern is regular. Most breeders tried to get rid of the remnant eumelanin. But I think that this pattern with dark spots on a white wings is very nice. But my experience is that it is difficult to fix this pattern.

Name giving: The result of the mutation factor is a regular and characteristic eumelanin pattern. This we call in Holland gezoomd. The translation in German is gesäumt. The English translation is edged. Most edged Bourke's are yellow. The yellow colour is bright and intensive. In this case it is a yellow variety of the edged Bourke. Yellow is the reference colour. Edged is the characteristic of the eumelanin. In the picture below you see a yellow edged Bourke I photographed in Besters place. This is a nice specimen of the yellow edged Bourke. He looks like a lutino except the dark face and the dank tips on the wing feathers. Caspers developed a yellow edged Bourke with a red suffusion over the yellow back. He called this apricot.

Combinations: The M-i factor can be combined with other M-factors that cause the fallow, opaline, pastel, etc. The pastel combination was used to reduce the melanin pigment in the head and the feather tips. The red pastel was used to develop the apricot.

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Copyright 2003 by Bob Fregeres

E-mail: fregeres@bourkes-parakeet.nl

1/2/04