FAQ: How to determine the reduction percentage of the eumelanin for colour mutations?
We often read in the standards and articles that, for example, pastel has a eumelanin reduction of +/-50%. But how is that determined?
Well, there is much confusion and misunderstanding about this reduction provision. To begin with, this is something typical of aviculture and especially with standards. Here the judges will determine how much reduction is expected with a mutation. These provisions are then included in the standards and articles.
But, scientifically it is not that simple and we notice that what we see does not always correspond with what actually happens inside the feather. For example, we see that the eumelanin in a pastel is ‘reduced’ for 50%, but in fact the same amount of eumelanin is produced as in a normal green, only the pigment granules are damaged in such a way that they can absorb little light and there is less reflection in the sponge zone.
The same with dilute, for example: the eumelanin is normally produced in the pigment cells, but the damage that the pigment incurs during transport in the feathers reduces the effect of the eumelanin. As a result, we see a bleached feather, whilst no less eumlanin is produced.
With euwing, we see a problem with the spread of the eumelanin in the featers. Here we notice that in certain feather fields on the body little or no eumelanin is deposited and that the eumelanin present is of very poor quality. In other feather fields we see that more eumelanin is present even as far as in the cortex of the feathers. But we cannot state that more or less eumelanin is produced in this mutation, because here, just like with opaline, the distribution of the pigments is disturbed. That is why, some researchers sometimes dare to call euwing the opaline mutant of the eumelanin. For good order sake: in opaline, both the distribution of eumelanin and psittacine are disrupted.
In dominant edged the eumelanin granules are damaged, but the distribution is also different, so that the concentration of the eumelanin in the barbs is different from barb to bard. This creates the visual effect of the edges in some SF edged birds. Should we also regard that as a reduction?
In SL ino we see a completely yellow bird and logically we believe that there is no eumelanin, but research has shown that pigment granules are indeed present and that eumelanin is actually produced. But here too, judges will describe these mutants as a complete reduction of the eumelanin. Why? Simple: they describe what they expect to see in an ideal show bird.
The only mutant where we can state that no eumelanin is produced in some feathers, is in the yellow feathers of a dominant pied bird. Here the pigment cells in the skin are absent. In all other mutants eumelanin is produced, but due to various damages that eumelanin has less or no effect, so that the (green – black) colour of a normal green feather changes. So, behind every visual reduction there is a typical developmental disorder of the eumelanin.
There is also no way to accurately measure the amount of eumelanin produced. The only thing we can do (for now) is to compare the concentration of the eumelanin present in a mutation with feathers of a normal green bird by means of the RAMAN technology. This indicates where the highest eumelanin concentration is present. But even that will no always explains the – visual – reduced colour of a feather.
That is why a percentage of visual reduction of the eumelanin is always defined on sight in standards and in articles when describing the birds. That makes It understandable for breeders and judges.
And remember: what we think we see, ….. isn’t always what we think it is 🙂