In the last few years great strides have been made in understanding and classifying color mutations in parrots. When I got started in cockatiels during the 80's the standard guide was The Encyclopedia of Cockatiels by George Smith. This book has a section in the back that explains the different color morphs in existence at the time. Smith also predicted the appearance of the Whiteface cockatiel and that albinos could be produced subsequently. What are missing from the book are explanations why color morphs appear that are different from the wild-type cockatiel. In the years since with the advent of the Internet, communication among aviculturists around the world has resulted in agreement on the classification of color mutations across parrot species.
Inte Onsman and Wessel Louw van der Veen of The Netherlands, Clive Hesford of the United Kingdom, and Dr. Terry Martin of Australia are prolific writers on the subject of Psittacine color forms and much of what is contained in this article is based on their published work. Dr. Martin's book, Color Mutations and Genetics in Parrots (2002) is an excellent resource to anyone who wants an in-depth understanding of the subject.
TYPES OF MUTATIONS
In a 2001 article Dr. Martin describes four classifications of color morphs. They are 1) Melanin altering (grey), 2) Psittacin altering (yellow and orange), 3) structure altering, and 4) pigment distribution altering.
Most cockatiel mutations fall into the Melanin altering group including Lutino, Cinnamon, Pied, Fallow, both Silvers and Emerald (more properly called Greygreen or Suffused Grey).
We are used to a different method of classification based on how a color morph is passed down (sex-linked or simple recessive and dominant), but this system is based on shared characteristics of the mutations. Dr. Martin divides the melanin altering group into three categories.
Albinism is the result of a defect causing melanin reduction (not elimination) in soft tissue as well as in the feathers. An example of this is the Lutino, wherein the eyes, skin, beak and nails show an almost total reduction in melanin as well as in the feathers. Albinism is variable. In the cinnamon, for instance, melanin is retained but altered in nature thereby giving the impression of reduced color. The alteration in melanin structure depends on the mutation involved and so we see different degrees of albinism. It is key to understand that the reduction of melanin in these types of mutations is never complete, even in the whitest Lutino. The Fallow and the Recessive Silver are albinistic mutations. These are known as qualitative changes.
Dilution is the result of a defect lowering the amount of melanin able to pass from the skin into the feather. The amount of melanin in the skin is generally unaffected. The Emerald (Greygreen) is a good example. They keep their dark beaks and feet, but lose varying degrees of melanin in their feathers. These are known as quantitative changes.
Leucism is the result of a defect that prevents the production of melanin altogether in affected areas of the body by directly disturbing the function of the melanin producing cell called a melanocyte. The unaffected areas, when present, have normal amounts of melanin. Since there is no melanin at all in the affected areas of the body, these feathers are pure white or yellow and the feet, beak, and skin are pink although in some forms of Leucism soft tissue can retain melanin pigmentation. The pied is an example of partial Leucism.
Psittacin is the name now used for the yellow/orange pigments seen in our birds. The term lipochrome describes a pigment (carotenoid) that is eaten and is able to deposit into the feather. It has since been determined that parrots synthesize (make in their own bodies) the pigment Psittacofulvin, which we call it psittacin for ‘short’. Anyone who ever tried to color-feed a cockatiel as you would a red factor canary can tell you that the bird's color remained the same, and this is the reason why. The whiteface mutation is caused by a defect rendering the bird is unable to produce Psittacin. There are also genetic modifiers that determine the amount of Psittacin deposited in the feather. Some cockatiels have lots of yellow and others appear nearly white in some areas. I know of a line of normals that have a golden face and orange cheek spot. Others have a reduction of the orange as well as the mask. We have seen some pumpkin-colored birds at our shows as well. These are not really recognized mutations; they are most often referred to as Psittacin modifiers. ‘Pastelface’ and the two Yellowface mutations are other psittacin altering mutations. Personally I do not like ‘Pastelface’ because the term suggests the Pastel mutation which alters melanin. That is why Dr. Martin uses Paleface in his book.
Cockatiels do not have a feather structure altering mutation per se, but there are modifiers to feather structure. Some cockatiels are very sleek and tend to have uniform feather color. Others look soft and have thick down with a lighter colored fringe on each feather. The latter will often have brittle feathers that break more easily than their sleek cousins. It is probable that the fringe is actually worn edges and not a lighter colored pigment. This phenomenon is well documented in the canary fancy, where they refer to hard and soft feathered birds.
Pattern alteration can be seen in the Pearled (also called Opaline) cockatiel. The mutation was seen almost exclusively in Australian birds, but now there are Opaline Indian Ringnecks, Plumheads, Lovebirds and also a couple of Conures and manifests itself a little differently in each species. In the cockatiel we see a bird with a mostly yellow tail, yellow mask and a variable amount of Psittacin and melanin in a distinctive pattern. I will bring you more about this fascinating mutation in future articles. It has been suggested that Emerald may fit this category in that each feather has a clear center and a dark melanin edge.
I hope this article has been informative and aroused your curiosity about color forms and their commonality between parrot species. There are vast resources available today on the Internet and if you poke around a little bit you will find a wealth of information.