The Enigma of the Florida Fancy and the European Isabel Zebra Finch
Heterozygous "Double splits" Florida Fancy and European Isabel. (male left, female right)

The Enigma of the Florida Fancy and the European Isabel Zebra Finch
Ever since Zebra finch breeders in the US and in Europe became aware of the similarities in color between the U.S. mutation known as the Florida Fancy and the European mutation known as Isabel, there were assumptions, miscommunications and confusion surrounding the true nature of these mutations and their relationship. It was only over time with lots of discussion between breeders on both continents, exchange of photos and now with extensive cross testing is the true nature of these mutations being understood.

A definition of each mutation, its method of inheritance, variations due to selection and results of combinations with other mutations, namely fawn, are needed first to understand what these mutations look like in their pure form before we discuss their relationship and combination.

Florida Fancy (FF)
The Florida Fancy mutation works by reducing the level of eumelanin (gray and black color in the normal Zebra finch coloration). It does not alter the Phaeomelanin or orange coloration of the plumage, mostly seen in males. The method of inheritance of the Florida Fancy is autosomal co-dominant and the mutation has two distinct phenotypes (appearances)  depending upon whether is single factor (carrying one gene of the FF mutation) or double factor (carrying two genes for the FF mutation). In double factor form the mutation is nearly white with all the orange markings on the male at full strength. In single factor form the reduction of eumelanin is approximately half that of the double factor form. This gives the bird a silver appearance and has in the past been referred to as “Silver Isabels”. More recently the birds are being referred to as “Florida Silvers” to avoid confusing the mutation with the European Isabels or indicating a combination with that European mutation.

It is the “Silver” form that is often confusing for people starting with the mutation, but if one thinks about the action of the gene, it makes sense. The gene acts to reduce the amount of gray/black coloration. With just one gene the mutation is able to suppress half the gray/black color leaving a silver-gray color. With two doses or two genes of the FF mutation, nearly all of the gray/black color is diluted to a near white color. What is somewhat surprising is that when FF is combined with Fawn, there is no visible indication of the Fawn gene. One would expect at least in the single factor FF that the birds would have a light or diluted fawn-brown color. This is not the case and the birds are still a light gray color.

When Gray Zebras of either sex are mated to double factor Florida Fancies, all single factor or silver-gray color birds are produced. An interesting and consistent coloration in these birds is that females are lighter in color than males. There is some variation in the amount of reduction seen in these silver-gray birds, but the difference between the sexes is very consistent in nest mates.

European Isabel
This mutation works in a similar manner by reducing the gray/black areas and is often exhibited in shows in the near white form with strong orange markings. The method of inheritance of this mutation is autosomal recessive. Birds that carry only a single gene for this mutation will not display it like the Florida Fancy can. The European show standards define the Isabel in Gray series and in combination with Fawn series by two different standards. In combination with Fawn the bird is selected towards a near white body with strong orange markings in the males. In the Gray form, a darker selection is used and these have a medium gray tone for the body.

Here is part of the confusion with the US Florida Fancy. In the US we would often hear that for the white type birds the mutation should be combined with Fawn, so many breeders tried to combine Florida Fancy with Fawn to achieve the white type bird. This was not necessary with the FF mutation. Also, Isabel combined with Fawn can still show light fawn colors in the body, but is generally selected towards a white coloration. So in Euro Isabel it is the combination with Fawn and breeder selection for white color that has produced the Isabel that resembles the double factor Florida Fancy.

If Euro Isabels are produced in a Gray series bird, they are generally selected towards a darker version that the Isabel gene is capable of. The Europeans have referred to this color as “mousey gray”. When the Americans first started seeing these birds, the resemblance to the single factor Florida Fancy was unmistakable and greatly confused us. Some began to think that these mutations were in fact the same thing. European breeders visiting Garrie Landry’s facilities in Louisiana would look at his single factor Florida Fancy and call them ‘Gray Isabel’ so the confusion was certainly mutual.

Color Description
So it can be seen that what is produced in both mutations, the Florida Fancy and the European Isabel, is a white type bird and a darker silver type bird. As I move forward with the discussion of the relationship with the two birds, to avoid confusion with the names and color of the mutations, I will simply refer to them as white type birds and silver type birds. Gray would refer to the normal or wild-type color variety.

The Discovery of European Isabel
My first discovery of European Isabel was from a line of Black Cheek Zebra finches that I was breeding. As a recessive mutation it remained hidden for some time and then when the line crossed and related birds were paired, a ‘dilute’ colored bird was produced. It was thought that the mutation might have been Recessive Silver at first, but this was later dismissed with some inconsistencies in color for that mutation. Namely, the amount of reduction that the breast bar and other black markings were receiving from this ‘new’ mutation. I then set forth on a breeding plan to isolate the Isabel mutation, combine it with Fawn and avoid the Black Cheek mutation as much as possible.

After a few generations, I started to produce my first Fawn Isabels. These birds were of the white type and resembled our Florida Fancies. My particular line was not selected towards the lighter color of the Isabel mutation and thus carried more color in the wings and back than a European standard would have liked, but I confirmed for myself that the mystery mutation was European Isabel. Both the Gray and Fawn varieties of the Euro Isabel were produced. The discovery of a European mutation such as this was not really a surprise since so many of the new mutations were imported from Europe and recessives genes were sure to be hidden in with the imported birds.

The Search for the Relationship Between Florida Fancy and European Isabel
The most obvious thing to do when trying to determine the relationship between the Florida Fancy and the European Isabel is to mate the birds together. This is precisely where I started, but the path to discovery after the initial pairing would still require a lot of test matings and dozens of young being produced to verify the results.

I started by setting up two pairs for breeding. A Florida Fancy male to an Isabel hen. The Florida Fancies were from two different sources and I selected sources that were unlikely to have mixed the birds with imported stock. The results were 100% of the young were of the white type birds. They resemble full Florida Fancies or full Isabels (light type) even though the birds only carried one gene of each mutation. This seems to indicate that the mutations have an allelic relationship or at least have some interaction. However, further tests would be necessary to show the exact nature of the relationship between these two mutations.

Some of the young from the FF x Isabel cross were then used in more follow up tests. First, I bred some of these F1 offspring (one gene FF, one gene Isabel) to a normal gray. First test mating was conducted with a Gray male and the second with a Gray hen. The results should show that the genes will segregate themselves in the offspring if the mutations are allelic. The single factor Florida Fancy birds should show up as the silver type birds and the single factor Isabels should appear as normals at ratio of 1-1.

What should not occur is for a bird to inherit both genes from the one parent carrying both genes as would only be possible if the genes were from different loci. This would indicate some sort of interaction between two unrelated genes rather than allelic relationship between two. This would reveal itself with the production of a White-type bird. All birds produced from these pairings segregated into Grays or Silver-type birds supporting the theory that the mutations are allelic.

The second test was to pair the F1 young (one gene FF, one gene Isabel) to a full Isabel bird. (sf FF/Isabel x Isabel). The results from this pairing should show that the genes have segregated themselves again and produced more heterozygous FF/Isabel and homozygous Isabels. All white-type birds should be produced. No Gray or silvery birds should be produced if the mutations are allelic. All birds produced were of the White-type which again supports the theory that the mutations are allelic.

Conclusions and Observations
The data from these test matings certainly suggests that the Florida Fancy and European Isabel are allelic mutations. Unlike the other known allelic series, the CFW and Lightback Zebra, the Florida Fancy and the Isabel have similar phenotypes, but different methods of inheritance. This similarity in phenotype but different inheritance has lead to much confusion. While an understanding of their relationship will shed light on some of the confusing breeding results some breeders in the U.S. have experienced, it is likely to add another level of confusion as well.

The total number of birds bred in each of the test breedings was sufficient to support the conclusions, but were the minimum number required to do so. I am confident in my conclusion that the Florida Fancy and European Isabel are alleles, but a second independent study would be ideal. The same problems of identifying the subtleties of these mutations in degrees of reduction caused by the mutation itself and selection from the strain used can make identifying nest young difficult. An example of this can be the similarities in color of a full European Isabel hen that is of dark form in Gray compared to a single factor Florida Fancy hen. So an independent secondary test with completely different strains of Florida Fancy and Isabel would be a great supportive study.

An interesting result of the heterozygous birds produced (one Florida Fancy and one Isabel gene) is that the birds were cleaner white than either of the parents used in the mating. This was true in the initial pairing of Florida Fancy X Isabel as well as those produced in the test matings later. In fact, the heterozygous birds could always be identified from the homozygous Isabels produced in the FF/Isabel X Isabel pairing. This seems to be a result of the interaction of the two mutations The strains used in my test breeding could have some effect as well, but there were two strains of Florida Fancy used in the initial tests. Further study of the color effects is warranted. It would also be worth studying the differences in color of the females versus males that are heterozygous for the mutations since female single factor Florida Fancies are consistently lighter in color than their male nest mates.

Hopefully this understanding of the interaction of the Florida Fancy and European Isabel will help breeders solve some confusing results in their Florida Fancy breeding. While European breeders have not had significant access to the American Florida Fancy, U.S. breeders have always had a great influx of imported birds. One of the most popular aspects of Florida Fancy breeding is to combine the mutation with Black Breasted (Phaeo), Orange Breasted and Black Face. The goal with these combinations is to increase the orange markings in the males as we have seen in photos from Europe. Of course the use of imported Zebras that already have Orange Breasted combinations has been the quickest path to the Florida Fancy combinations. Not surprisingly some of these imported birds have been carrying the recessive Isabel mutation. So the crossing of Florida Fancy and Isabel has occurred. It has lead some to be confused by the results and had some simply claim that they are the same mutation. Understandable since the direct mating of a Florida Fancy to European Isabel would result in 100% white-type birds. The expected result. It is further down the line in breeding that unexpected results can occur. Now breeders can begin to sort out the results.