The Bourke's parakeet has brown eumelanin. The difference between black and brown eumelanin is the degree of oxidation. The granules (granules = very little grains) of both types, black and brown, have the same form and format. The difference is qualitative. Stronger oxidation means darker eumelanin grains and darker feathers. Black eumelanin means a higher degree of oxidation. The brown eumelanin has a lesser degree of oxidation. The Bourke has brown eumelanin, eumelanin with a lesser degree of oxidation. Neophema have black eumelanin
Brown barbs of a tail feather
The plumage of the Bourke is characterised by an excessive amount of eumelanin. There is a strong concentration of brown eumelanin in the barbs and the barbules. In the barbs of the common type barbs (barbs without a blue structure) the eumelanin is spread in the whole barb. In the barbs of the structural type (barbs with a blue structure) the eumelanin can be grouped in the centre, around vacuoles in the medullary cells of the barbs.
Blue colour. The blue colour is caused by two factors, a combination of a sponge zone with a grouping of the melanin in the centre of the barbs. When the melanin in the kernel is grouped round vacuoles in the medullary cells, it forms a dark layer that absorbs the light of the wavelengths that are not reflected. This absorbing background is necessary for the blue colour.
In the Bourke there is also eumelanin deposed in the cortex. This eumelanin is responsible for the typical colour design of the wings and the breast of the Bourke. The pigments red and yellow are deposed only in the cortex. When there is a lot of eumelanin in the cortex, other pigments can be covered. Black or brown pigment are covering the other pigments. We call this melanism. In nature we find sometimes melanistic birds or melanistic varieties of birds. The Bourke has a lot of brown pigment. The yellow pigment is hardly visible. The red colour in the breast becomes dark rose. Only in places where less eumelanin is found, like the belly, the red pigment is more visible. The melanin fails in the margins of the wing coverts. If there is yellow or red pigment deposed, it is visible as red or yellow colour. In the original wildtype this margins are yellowish white.
How do we know that the eumelanin is covering the other pigments? By studying the cross sections of barbs of the wildtype and colour varieties. When a reduction of the eumelanin takes place by mutation, the hidden colours are appearing.
Not all the mutations are reducing the amount of eumelanin. It is possible that the amount of eumelanin becomes bigger. This gives way to a further increase of the influence of the eumelanin pigment. When the amount of melanin granules is very high. The brown plumage becomes almost black. In this very dark Bourke the red pigment is hardly visible.
Dark upper tail coverts
Eumelanin production process
Two types of melanin
Eumelanin is a pigment. We know two types of melanin. The eumelanin and the phaeomelanin. The eumelanin counts for the brown and black colours. The eumelanin granules appear under the microscope as rod like particles. The pheomelanin counts for the red brown and yellow colours. These granules have an round form. The Bourke, and all other parakeets, have only one type of melanin, the eumelanin.
When the hen is breeding, the little embryo is growing. Very early in the development of the embryo, special germ cells, the melanoblasts, are developing (Melas (Greek)= black, blast=germ ). The germ cells are moving to the places in the skin, where the feather shall grow out of the skin. A genetic factor counts for the distribution of the germ cells. The destination of each germ cell is the base of a growing feather, in the follicle, the increase of the skin.
Production of eumelanin
Lets try to get the essence of the production process. The production cells can be seen as little plants. For every factory product is needed raw material and a specific production procedure. Often this procedure is a trade secret. The procedure of the production of the eumelanin granules is unravelled step by step by biologists.
The first production line is the development of the pigment in the feathers. In the horny parts, the toenails and the beak we find this eumelanin also. Another production line is serving the pigmentation of the iris. In the eye the melanin production is starting after four days. In the feathers and horny parts after seven days. A mutation can influence one of this lines but also both lines. In some mutations only the colour of the feathers and horny parts is altered. But in the some mutations not only the colour of the plumage is changed but also the colour of the eye.
From germ cells to production cells
When the germ cells are reaching there genetically fixed destination, they take a new form, the melanin production cells. They are named melanocytes (Melas (Greek) = black, cites (Greek) =cell ). This production cells are developing long processes, the dendrites. All tissue cells in the body of man and birds are round, except nerve cells and melanine production cells. To produce eumelanin grains, raw material is needed, named tyrosine. This is a special amino acid, that is made out of white of egg, found in the diet. Enough riboflavin, an amino acid found in the diet, is very important for the deep black feathers. Amino acids can not laid in the body like fat. So they are not stored. Therefore an albuminous diet is important in the growing and colouring of the feathers. Do not forget to give your birds a good diet before and during the breeding season.
From raw material to melanin grains
What further is needed is an enzyme, named tyrosinase. This is stimulating the oxidation of the raw material (binding tyrosine molecules with oxygen atoms). Without this enzyme the production does not start. More than one oxidation is occurring in this phase of the melanin formation. In producing brown eumelanin the oxidation stops earlier than in producing black eumelanin. The end products of the production process are microscopic little brown round eumelanin particles.
Deposition of the eumelanin
The long processes of the production cells spout the drips of plasma with the eumelanin particles neatly packed in a cell membrane in the growing feather. This has to be done on the exact moment at the right place and in the just quantity. This is genetic regulated. Every production cell is supplying several cells. When all pigment is gone this production cell will be destroyed. A lot of production cells is needed. The new feather cells are fixed in a definite form, by an albumen, named keratin. When the feather is ready, the form, structure and colour of the feather are fixed. A colour pattern of the feather can be very complicated. The production, transport and deposition has to be very exact.
Colour, form and format of the grains
The colour of the feathers of can be more brown or more dark brown, according to the amount of melanin grains, the form and format of the grains and the oxidation of the grains. The wildtype Bourke has a huge amount of long, brown, eumelanin grains. The main colour of the plumage is earth brown coloured. The design of the wings and the undulated breast is due to eumelanin in the cortex.
Melan formation is a very complicated process. In spite of the precise control by the genes somehow goes wrong. I will represent the production and deposition of eumelanin as an industrial process. I am aware of simplification, but I think it is a good mean to the end, to get insight in what mutations really are.
Suppose there is a firm that is producing some products for building companies. The business is decentralised. Production units are set up near to the building places. The supply of raw material should be well arranged. The production has to be sychronised with the building process. Very important are the production start and the amount of building material to produce. The delivery at the building site, has to be punctual and at the proper location. The precise instructions about the production process that are laid down in the production plan have to be followed. Every building place has a different need. Sometimes more production units are needed for the same building place. The distribution of the final product on the spot can differ also.
Yet we can try to formulate the controlling criteria for the formation of the eumelanin.: Control of the quality of the final product, format and form of the melanin grains (01) and granules with the prescribed colour (02). Control of the quantity, proper amount of grains (03). Process evaluation is needed also. Controls on the macro level: Distribution of the germ cells. Enough germ cells (04) . Distribution of the production units about the whole plumage according to the planning (05). Controls on the micro level: Development of good functioning production cells out of the germ cells (06) Enough raw material needed for production (07). Enzymes to start and to maintain the production (08). Development of the processes of the production cells as a transport medium (09). Deposition of the melanin, neatly packed in cell membranes, at the prescribed place in the barbs, barbules and hooks, in the kernel or in the cortex (10) The grains have to be deposed at random in the barb, but sometimes they have to be concentrated in a layer (11). A good carrying away of the remainders of the material, by the blood vessels. Fixation of the feather, inclusive the pigments by the keratin.
Analysis of production faults and the effects in the plumage
01. Granules of different form and format are found in the fallow colour variety of the Bourke. The grains are more elliptic and smaller. The format is not constant. Most this is combined with a decrease of the amount of grains. The form and format don't meet the criteria. The effects are: The colour of the whole plumage is lighter than normal. The brown colour becomes light sand coloured brown. There are other effects too. The horn parts, bill and nails are flesh coloured. The eyes are red. Fallow is a name used in praxis to give an impression of the changed colour of the plumage.
02. Eumelanin grains of the wildtype Bourke are brown because of oxidation. According to Kop, there are more oxidation phases. To produce black melanin, all phases are needed. In the case of brown melanin of the wildtype Bourke, the oxidation stops earlier. In the light cinnamon Bourke the colour is due by a lesser degree of oxidation then the wildtype. Most there is a reduction of the amount of grains also. Beckmannn found a reduction of 50%. In Holland the name isabel was used. We have to reserve this name for birds with two kind of melanin, the phaeomelanin and the eumelanin. When one of the melanins is missing the name isabel is used. Steiner (1935) called this isabellism. Parakeets have only eumelanin. In the case of the colour variety of this Bourke I use the name light cinnamon.
03. There is a decrease of the amount of eumelanin in every feather, in the whole plumage. This is causing a dilute of the colour. In Holland they use the term pastel. Beckman found a decrease of eumelanin of about 100% in the barbs and 50% in the barbules and hooks. The colour of the plumage depends on the possession of psittacine pigments. Yellow in the case of yellow pigment. Rose in the case of red pigment. Most fanciers in Holland were breeding the yellow colour variety. The rose variety was developed in Holland in the early seventhies. This is not an opaline!
04. There is a distribution problem on the macro level. A shortage of germ cells makes that there are not enough germ cells available for every feather follicle. No germ cell means no production cell also. In the brown plumage of the Bourke we find white feathers. We call this pied. The blue feather that is missing the absorbing dark ground becomes also white. Feathers with red or yellow pigment become red or yellow.
05. Changed distribution of the production units on the macro level. There is a change in the melanin pattern (melanin in the cortex) on the back. The opaline Bourke has a broad white under wing stripe. In perching this is seen as a white triangle on the flights. Another characteristic is the fine black stripes on the back, remnant of the fore ground melanin. Another distribution means less melanin in the feathers on the back, rump and tail, more melanin in the wings. Selection is possible also. The first opaline Bourke was a rose opaline. Rose because of the mix of red and brown pigment. Today there are opaline with a red plumage. This means that the amount of grains is diminished.
06. Some production cells don't function well. In Holland they used the name gezoomd. A translation of the name spangle. Van Eerd (Holland) gave a explanation of the typical pattern. The early production of melanin becomes to strong. The production cell burst. Afterwards no grains are formed any more. When this destruction comes very early in the production and deposition of grains, we have feathers without melanin except a dark tip. The colour of the back becomes the colour of the other pigments, yellow or red or yellow with a red suffusion. When this is happening later, we become less spangled Bourke's. The name spangle does not fit. The inheritance is not the same. Actually this is a kind of pied. The distribution is regular. There is a big variability in the loss of melanin. Fethers never lose all the melanin.
07. When there is a shortage of raw material, the albumen that are necessary, a pied plumage can develop. This is due to a environmental factor. The oied pattern does not inherits. We call this a modification.
08. Sometimes there is no oxidation. The cause can be a lack of activity of the enzyme that works as catalytic by the start of eumelanin formation and the process of oxidation. No eumelanin grains are formed. An ino, lutino or rubino is the result.
09. When the production cells develops no processes, or deformed processes there is no melanin deposed. Sometimes we find traces of melanin in the flights. This is another cause of the ino.
10. Not all changes of the production means lighter feathers. It is possible that there is a more strong production in the whole plumage. We speak about a hyper function of the production. The feathers become dark brown, almost black. When there is found also eumelanin in the cortex the other pigments are covered. The Bourke becomes melanistic characteristics.
11.Eumelanine deposition in the barbs has to take place on the right moment on the right spot. The distribution on the micro level can be changed. In stead of spreading the grains in the barb randomly, grouping of the grains in the middle cells takes place. This grouping in combination with an altered structure of the barbs gives the possibility of blue and green feathers.
Changes of the micro structure of the feather
12. We give also a description of the micro structure, changed by a mutation of a gene. An alteration occurred in the barbs of the normal type. When this barbs change in barbs of the structural type a sponge layer develops. In the wildtype we find in the feathers of the head, hind neck, back and part of the tail feathers without a sponge layer. When this development is combined with a change in the grouping of the grains (11) then a blue colour is possible. Green colour is showing up when there yellow pigment in the cortex.
13. The wildtype Bourke has a restricted amount blue feathers. These feathers have no yellow pigment in the cortex. A change is realised in this wildtype blue feathers. The colour became cobalt blue and violet blue. An explanation can be the narrowing of the little channels of the sponge zone. The violet is visible in the under tail coverts, the blue frontal band of the cock the bend of the wing and the outer vanes of the wing feathers and some tail feathers.
Changes in the psittacine pigments, red and yellow
14. The formation of the psittacine pigments has to be synchronised with the growth of the feather. These pigments come in the cortex via the blood vessels. In the formation of this pigments a hypo- and a hyper function came into being. Probably by selection. In the case of a hypo function less pigment is deposed. In the case of a hyper function more pigment is deposed. Also the extension of the pigment deposition in the back was possible. This extension was already seen in the first yellow pastel (1954) The extension was due to selection.
A mutation is an unexpected accident that is happening during the reproduction of the DNA. The result can be the change of a gen. The altered gen we call a mutation factor. Most Bourke's mutations during the last fifty years are eumelanin mutations. Melanin mutation factors (M-factors) of the Bourke are inheriting independent of mutation factors of the psittacine (P-factors) or mutation factors of the structure (S-factors). Change in colour of the plumage is caused by the altered genes, the mutation factors.
In the moulting period all feathers are replaced, the old feathers are cast off, new feathers are developing. The whole process of melanin production and deposing in the growing feather is repeated. The juvenile moult takes place after ca. four months. Yet the feathers become their definitive colour. The moult after the breeding season is once a year. The moult is regulated because the possibility to fly has to be preserved.
Copyright 2003 Bob Fregeres. All rights reserved