This is an extract from a post made by
the late Mark Shipway in the BBS Yahoo Group on 11/10/2001, and
definately has some worthwhile points to consider.
"I
am in the midst of preparing some ideas about standards and types. As a starting point I thought I'd prepare the ideas below about bengalese
colour. Please bear in mind that this is a theory I have developed and have based it on my experiences and what I have read in other
articles, journals etc in foreign magazines on Bengalese. I have no
scientific data to back my conclusions and am prepared to accept that
some of my views are open to challenge. Having said that I believe that
this information forms the basis of what we do know to date about
bengalese colour.
I believe its important we know about bengalese
colour before we go about developing colour standards. There is also a
picture for you to view.
To report on breeding progress. I have
some young in the nest from a large pied cock (source Deon) to a small
self hen. So I am one step closer to producing larger selfs.
Feelfree to make comments on the information below.
Part 1 - Feather colour in Bengalese
Feather colour in Munias is produced by melanin. Two types of melanin occur in Bengalese,namely:
· eumelanin
· phaeomelanin
Eumelanin
Eumelanin
canbe either black eumelanin or brown eumelanin. Chocolate
Bengalese have both. The "Euro" bengalese is effectively a bird with extensive black melanin caused by both selective breeding and introduced
from hybridisation with birds with high amounts of this type of melanin
e.g.. Blackheaded nuns.
Australian Chocolates show black eumelanin
in the face and to varying degrees down the throat to the breast and on
the wings and tail. Brown eumelanin is evident almost everywhere.
Chestnut Bengalese have some brown eumelanin but no black eumelanin.
Eumelanin in its purest form is the grey mutation.
Phaeomelanin
In
its purest form, the fawn bengalese shows virtually only Phaeomelanin.
The fawn bengalese should really be called a "phaeo" rather than fawn,
cinnamon, ginger or red brown. It is not a true fawn mutation like say
the fawn Zebra finch. The only example of a true fawn/cinnamon mutation
in munias in Australia that I am aware of is the Fawn Java Sparrow.
Both chestnut and chocolates, like fawns, have varying degrees of phaeomelanin.
A bengalese without any eumelanin or phaeomelanin is white.
Chocolate has the following melanin:
· Black eumelanin
· Brown eumelanin
· phaeomelanin
The future objective with the colour of this mutation should be to increase the amount of black eumelanin.
Chestnut has the following melanin:
· Brown eumelanin
· phaeomelanin
The
future objective with the colour of this variant should be to settle on
the ideal shade and focus on improving its evenness. I believe that the
chestnut should be a grade half way between the chocolate and the fawn.
Fawn has the following melanin:
· phaeomelanin
The
future objective with the colour of this mutation is to darken up the
phaeomelanin as much as possible so that it matches Dutch red browns. I
believe some individuals are almost there. I am not sure whether the
increase in black melanin in chocolates will assist to intensify the
phaeomelanin, time will tell here as we experiment further.
Dilutes are really
pastels
which have a quantitative reduction in both eumelanin and phaeomelanin
to varying degrees between individual birds. It is for this reason that
it is not correct to call a "chestnut" a chocolate dilute because,
whilst there may be some reduction in eumelanin, there is no reduction
in phaeomelanin.
Colour variability between individual birds of the same mutation
Within
any particular colour variety it is apparent that intensity of colour
varies between individuals. This is particularly relevant in the
chestnut mutation (possibly because there is high variation in brown
melanin) which has given rise to my confusion in the past as to whether
two particular birds are different shades of chestnut or are two
different mutations. This is what brought about the name "smokey" and
"cream" but I now see these names as not relevant.
Why is this?
The most probable explanation for colour variability in bengalese is the
effect of multiple alleles. Unlike most other species of birds, in
bengalese an unknown number of alleles control colour. They all share
the same position onthe chromosome but only two can occupy the position
in any particular individual bird. Some combinations result in darker
colour whilst others resultin in light colour in graduations down to a
colour regarded as dilute.
Multiple Alleles
It
is importantfor a bengalese breeder to understand what multiple alleles
means and how it operates because it is central to the relationship
between:
· Chocolate, chestnut and fawn
· The intensity of colour within any particular colour variant
· possibly, the relationship between pied birds with varying amounts of white.
On
the latter point, more research is needed to be sure. I have made this tentative conclusion based on incomplete past breeding experiences.
Chocolate, Chestnut and Fawn
On
the basis of multiple allele theory, chocolate is dominant over
chestnut and fawn. Chestnut is dominant over fawn. No chocolate can be
split to both chestnut and fawn. The only way to produce chocolates,
chestnuts and fawns in a particular nest is to mate a Chocolate/ fawn to
a chestnut/fawn. Please view the attached photo ofthe three mutations
side by side. The fawn can be distinguished from a chestnut on the basis
that eumelanin remains in the bill and legs of the chestnut. There is
little, if any, phaeomelanin in the bill and legs of a bengalese.
End of Part 1
Kind Regards
Mark Shipway"
