A study on the breeding of the Siskin (Carduelis spinus) in new colour varieties

Study on the breeding of the Siskin (Carduelis spinus) in new colour varieties

JM EYTORFF
International Judge O.M.J (C.O.M) European Fauna and Hybrids
Head of the European Fauna and Hybrids Section of the C.N.J.F

When the first colour mutations in the Siskin appeared in the 1970s, few breeders could have imagined that this charming finch would, after a few decades, display such a diversity of colours. The hard work, selective breeding and curiosity of breeders specialising in this field have helped to broaden the range of domesticated varieties, making the siskin the most interesting species to breed for those wishing to combine the pleasure of breeding with genetic research.

Allow me to give a brief history of the colour mutations that have appeared in this species.

The very first mutation discovered was, as with many species, the brown mutation (a sex-linked, recessive factor). Shortly afterwards, a Dutch breeder, Dick den Hood, acquired a green bird exhibiting a dilution of eumelanin, which he named ‘pastel’. Breeding trials involving this mutation demonstrated that the ‘pastel’ factor was an autosomal dominant trait, rather than a sex-linked recessive trait as in the canary. Many years later, the COM, in order to avoid any confusion with the true pastel factor, decided to call this mutation ‘dilute green’. However, the ‘dilute green’ mutation is still referred to as ‘pastel’ in some countries, whilst the ‘pastel’ factor (which is sex-linked and recessive) also exists in the siskin.

The combination of brown with diluted green made it possible to breed for diluted brown. Mating a diluted green male with a brown female does indeed produce young females that are green and diluted green, and young males that are green and brown-carriers, as well as diluted green males that are brown-carriers. It was these green-dilute males carrying brown that made it possible to produce the first brown-dilute birds. For the record, mating a dilute green male carrying brown with a brown female produces females that are: green, dilute green, brown and dilute brown. And males that are: green carrying brown, dilute green carrying brown, brown and dilute brown.

At the time, many believed that an autosomal dominant × autosomal dominant cross could not produce offspring, based on known failures in autosomal dominant × autosomal dominant crosses (as in the case of the crested factor in the Gloster). This was a mistake, for – once again thanks to the curiosity of certain breeders – the combination of diluted green × diluted green gave rise to the first double-diluted greens. It was then simply a matter of mating diluted brown × diluted brown to obtain the double-diluted brown, which was not long in coming.

Time passed, and a female bird carrying the agate mutation (a sex-linked, recessive factor) appeared in a breeding programme. This new development marked the beginning of a new phase. The combination of brown with agate produced greens that carried both the agate and brown alleles. Crossing-over and a stroke of luck led to the emergence of a new mutation: the isabelle.

The rest is history, and we now have an impressive range of colour mutations in our breeding programme: brown, agate, isabelle, dilute green, dilute brown, dilute agate, dilute isabelle, double-dilute green and double-dilute brown.

In 2003, after many years of experience with colour-mutated siskins (I began breeding colour-mutated siskins in 1978, and having published articles a few years ago in *Les oiseaux du Monde* on the study of the siskin in colour mutations), I decided to continue the adventure and attempt to produce a double-dilute agate specimen, or even a double-dilute isabelle. Up until then, the various discussions I’d had with other experienced breeders specialising in this field had suggested that the chances of success were slim. There was talk of mortality in the egg due to the fragility of the embryos, mortality at hatching, and behavioural problems in the young.

By mating a dilute agate male carrying the isabelle gene with a dilute isabelle female, I thought that with a bit of luck… And in breeding, regardless of the quality of the facilities, the bloodline, the diet or the time spent observing, you also need a bit of luck.

In the same vein, I mated a diluted isabelle male with a diluted isabelle female in order to produce double-diluted isabelle offspring. From this pair, I obtained two broods and no young. When the eggs were fertilised, the chicks died in the egg.

The diluted agate × diluted isabelle pair gave me a first clutch of five eggs in late April, all of which were clear. I attributed the lack of fertilisation in this first round to the birds’ youth. In May, the diluted Isabelle female began a second clutch. Of the four eggs laid in the nest, two appeared to be fertilised, but I preferred not to check the nest too closely due to the parents’ nervousness.

After 13 days, the first eggshell was lying on the floor. I had to wait until the following day to check the nest as the female wouldn’t budge a muscle. Using a mirror, I could see two chicks that were particularly pale (both skin and down). I thought they might be diluted Isabelles. At 7 days old, whilst ringing them, I realised that I did indeed have two diluted Isabelles and that I would have to wait a little longer to see if they were double-diluted agate or double-diluted Isabelle. I always ring them around 7 pm; the rings are covered with plaster, which minimises the risk of them coming off. Feeling confident, as this method gives me a virtually 100 per cent success rate, I went to check the aviary a quarter of an hour later. To my great dismay, the two chicks were lying on the floor, still ringed, as the parents had thrown them out of the nest, unable to remove the aluminium rings. I placed the chicks back in the nest and waited for about ten minutes. The female returned to the nest. I thought this incident would have no consequences. Just to be on the safe side, I went back a quarter of an hour later. The chicks were on the ground again, but this time I noticed that their legs were broken. Unable to remove the rings, the parents had attacked the chicks’ legs. I thought then that all was lost. However, refusing to give up, I decided to cut off the rings, disinfect the wounds, realign the legs in relation to the fractures, and place the chicks back in the nest, taking care to maintain the correct alignment of their legs. I knew that cartilage heals quickly in young birds, but I must admit that at that moment I didn’t really believe it, and I had all but given up hope for my Isabelles. The chicks were accepted and remained in the nest, so all that was left to do was wait.

The days passed, and the chicks were still in the nest and alive, as from time to time I could catch a glimpse of their heads whilst the female was feeding them.

At fifteen days old, against all expectations, the first chick left the nest, showing no signs of leg deformity. The following day, the second chick was also on the perch, unharmed. Whilst rearing the chicks, the female had simultaneously built a second nest and plucked all the feathers from her chicks’ backs to line the bottom of it. The chicks looked like two Isabelles, but I began to have some doubts when I noticed a charcoal-grey colour at the tips of their growing flight feathers and tail feathers. As the days went by, the back feathers grew back but with a predominantly grey-green hue; I began to think that my ‘Isabelles’ were actually Agates. Apart from the back, the rest of the plumage was predominantly yellow streaked with light grey.

After weaning and, above all, moulting, I had confirmation that I hadn’t reared any Isabelles. One of the two young birds was predominantly yellow, with grey streaks and a greenish-grey back; the other was different, displaying more melanin and less lipochrome. The first young bird was a double-dilute agate; the other is a mutation currently being identified. Both young birds were females. The results were spectacular and demonstrated that mating a diluted agate with a diluted isabelle could produce double-dilute agates, with a bit of luck…

Following on from 2003, the 2004 season was a year of experimentation with the ivory colour, and I was fortunate enough to see ivory, diluted ivory and double-diluted ivory birds hatch at my breeding station.

The 2005 season was much like the 2004 and 2003 seasons, full of excitement and surprises – judge for yourselves:

My aim, in fact, was to produce new colours by combining the ivory factor with the classic mutations recognised by the C.O.M – brown, agate, isabelle – or even the dilute factor.

Various matings were carried out during the winter months, including, amongst others, the following pairs:

• Green male (wild-type phenotype) carrying Isabelle, brown, agate and ivory X ivory female

• Green male (wild-type phenotype) carrying Isabelle, brown, agate and ivory × diluted ivory female,

• Dilute green male carrying isabelle, brown, agate and ivory X diluted ivory female

As a reminder:

Isabelle, brown, agate and ivory are recessive, sex-linked factors

The dilute factor, however, is an autosomal dominant trait.

• Mating a green male (wild-type phenotype) carrying isabelle, brown, agate and ivory X an ivory female

may indeed produce the following results, provided that crossing-over occurs, which is by no means guaranteed:

As a reminder, crossing-over is the exchange of segments between two paired chromosomes, causing a crossover. In this case, two traits linked to the same chromosome may become separated. Conversely, two traits previously linked to different chromosomes may become linked.

Young females:

Green
Isabelle
Brown
Agate
Ivory
Isabelle ivory
Brown ivory
Agate ivory

Young males:

Green (wild-type phenotype) carrying ivory
Ivory
Green (wild-type phenotype) carrier of isabelle, brown, agate and ivory
Green (wild-type phenotype) carrier of brown and ivory
Green (wild-type phenotype) carrier of agate and ivory.

• Mating a green (wild-type) male, carrier of isabelle, brown, agate and ivory, with a diluted ivory female

May indeed produce the following results, provided that crossing-over occurs with regard to the ivory factor (ivory isabelle, ivory brown, ivory agate):

Young females:

-Green
-Isabelle
-Brown
-Agate
-Ivory
-Isabelle-ivory
-Brown-ivory
-Agate-ivory
-Diluted green
-Diluted isabelle
-Diluted brown
-Diluted agate
-Diluted ivory
-Diluted ivory isabelle
-Diluted ivory brown
-Diluted ivory agate

Young males:

-Green (wild-type phenotype) carrying ivory
-Ivory
-Green (wild-type phenotype) carrying isabelle, brown, agate and ivory
-Green (wild-type phenotype) carrying brown and ivory
-Green (wild-type phenotype) carrying agate and ivory.
-Dilute green carrying ivory
-Dilute ivory
-Dilute green carrying isabelle, brown, agate and ivory
-Dilute green carrying brown and ivory
-Dilute green carrying agate and ivory.

The range of possibilities is, in theory, impressive. However, a great deal of luck is always required, and one must always take crossing-over into account.

• Mating a dilute green male carrying isabelle, brown, agate and ivory with a dilute ivory female

may indeed produce the following results, provided that crossing-over occurs with regard to the ivory factor (ivory isabelle, ivory brown, ivory agate, dilute ivory isabelle, dilute ivory agate, dilute ivory brown):

Young females:

-Green
-Dilute green
-Isabelle
-Dilute Isabelle
-Brown
-Dilute brown
-Agate
-Dilute agate
-Ivory
-Diluted ivory
-Ivory isabelle
-Diluted ivory isabelle
-Ivory brown
-Diluted ivory brown
-Ivory agate
-Diluted ivory agate
-Diluted double green
-Double diluted brown
-Double diluted agate
-Double diluted isabelle
-Double diluted ivory
-Double diluted ivory brown
-Double diluted ivory agate
-Double diluted ivory isabelle

Young males:

Green (wild-type phenotype) carrying ivory
Ivory
Green (wild-type phenotype) carrier of isabelle, brown, agate and ivory
Green (wild-type phenotype) carrier of brown and ivory
Green (wild-type phenotype) carrier of agate and ivory.
Dilute ivory
Dilute green carrying isabelle, brown, agate and ivory
Dilute green carrying brown and ivory
Dilute green carrying agate and ivory.
Double-dilute ivory
Double-dilute green, carrier of isabelle, brown, agate and ivory
Double-dilute green, carrier of brown and ivory
Double-dilute green, carrier of agate and ivory.
Double-dilute green, carrier of ivory

Of course, there is theory and there is reality, and luck must play a part for new mutations to appear.

I was fortunate enough to have this happen, as some of the sought-after specimens were born at my cattery. New mutations such as ivory-dilute brown, ivory-brown, ivory-double-dilute and, above all, agate-ivory-double-dilute are now established; attached are a few photographs showing some of these birds in colour after their juvenile moult.

Having observed them in the breeding programme or bred them myself, the following mutations now exist in the Eurasian siskin (Carduelis spinus):

• Brown
• Agate
• Isobel
• Dilute green
• Dilute brown
• Dilute agate
• Dilute Isobel
• Double dilute green
• Double dilute brown
• Double dilute agate
• Ivory
• Brown ivory
• Ivory agate
• Dilute ivory
• Ivory-dilute brown
• Ivory-dilute agate
• Ivory-dilute isabelle
• Double-dilute ivory
• Ivory-dilute brown double-dilute
• Ivory-dilute agate double-dilute

I haven’t yet had the chance to see the double-dilute isabelle, the double-dilute isabelle ivory, and the isabelle ivory, but it certainly won’t be long now – perhaps as early as the 2006 season.

We can still dream of discovering the blue mutation that will produce all the colours already established with the white factor. For ‘ivory’ is incorrectly referred to as ‘blue’. I hope that one day it will appear in one of our Tarin des Aulnes breeding programmes.

That, in a few lines, is why, in my view, the Eurasian siskin in its various colour mutations is undoubtedly the most interesting species within European fauna, both in terms of breeding and from a scientific perspective. The Goldfinch, too, is experiencing a phenomenal boom – a topic I shall cover in a future article.