Variegation, part 1: the pied factor

Those of you who have followed the history series will know that, thanks to the illustrations of Marcus Zum Lamm, variegation first appeared in domestic canaries some time around 1580 in Germany. By the turn of the seventeenth century, Hervieux’s list informs us that French canaries were being graded according to their colour and markings rather than their song. Within a few decades, in eighteenth century London, a strain displaying a very refined form of variegation had been established: the fine spangled sort.

That is a span of over 150 years; we know some of the major milestones in the development of variegation in canaries, but little of the detailed progress. Wouldn’t it be interesting if we could follow a similar development in a modern cage bird, so that we can analyse progress with the benefit of photographs, first-hand reports and a knowledge of genetics? Perhaps we can.

Have a look at the photo at the head of this article (1). Note the dark wings and tail and the extensive areas of clear feathers on the body. A good example of a spangle-back canary? One of Piet Render’s birds?  No.

The bird is not even a canary, but a pied greenfinch (2) which appeared in Cage & Aviary Birds in 2003. Two important articles about pied greenfinches appeared that summer. The first was by Bob Partridge published in the 28 June edition (3). Bob has appeared on FSS before, and is an authority on British mules and their hybrids (4). It was he who established the pied greenfinch mule in aviculture.

Bob acquired his pieds from a breeder named Bill Roberts from Lincolnshire in 1987. Bill had bred some unusually coloured greenfinches and invited Bob to look at them. Bob realised immediately what they were and they mutually agreed that the mutation would have a better chance of becoming established if Bob took charge. More pieds appeared in the aviaries of Angela Timus from Nottinghamshire in 1989. These birds appear to have been unrelated and together laid the foundations for the pied greenfinches we see in aviculture today.

Bob’s article was a report about the progress he had made with pied greenfinches over the intervening 15 years. The article is the greenfinch equivalent of Marcus Zum Lamm’s account of variegated canaries between 1580 and 1600, but with much more detail and colour photographs! It is destined to become an important archival resource.

Bob made several observations about their phenotype and how he had improved their size and the quality of the markings. The early birds had light spots on the head wing or tail, but gradually specimens displaying larger patches of clear feathers were produced. The pattern of light feathering was unpredictable, ranging from 100% clear to visually 100% dark and everything in between.

He initially thought that the pied factor was an autosomal recessive gene, but soon realised that it was ‘far more complex than that’ when the results of crossing pieds with other mutations defied theoretical expectations. Fortunately, Dave Henderson, in an article published five weeks later (5), was able to propose a mode of inheritance that explained the anomalies: it was a co-dominant trait (6).

Co-dominance means that the alleles (7) from both parents are expressed in the offspring. In the case of the pied greenfinch, the genes that control the production of melanin (dark pigments) are competing against a gene that has a tendency towards lightness. The resulting phenotype can vary from clear and ticked, through varying degrees of variegation ( 50% being the ‘ideal’ for show purposes) to visually dark birds. That lightness can appear not only in the feathers but also in the legs and claws, but it may not be obvious (8).

For all its similarity to a spangle-back, the pied greenfinch at the head of this article is a fluke; its markings may look attractive but they are not derived from the mutation that created the London Fancy. How do I know? Bob has confirmed to me that the light feathers of a pied greenfinch are present in the nest. The London Fancy’s light contour feathers emerged during the moult. They were created by an entirely different process that I will examine later in this series.

Footnotes:

  1. Breed selectively for pied greenfinches by Dave Henderson, Cage & Aviary Birds, 30 August 2003, p.12. I have masked out the text that was over-printed on the photo, in order not to ‘give the game away’. The text stated “Dave Henderson tells us why he feels there is more to the pied greenfinch mutation than the simple dominant/recessive approach to genetic inheritance can explain”. Unfortunately, neither the breeder nor the photographer are named, so I cannot credit them.
  2. Carduelis chloris. ‘Pied’ is the term used by British bird fanciers and budgerigar breeders, whereas ‘variegated’ is used by canary fanciers. Both are forms of ‘leucism’ and involve the loss of melanins in the plumage.
  3. The elusive pied greenfinch, by Bob Partridge, Cage & Aviary Birds, 28 June 2003, p14. The birds are Bob’s but the photographer is not named.
  4. I consulted Bob in connection with the variegated siskin mules which Dr. Galloway claimed held the key to the origins of the Lizard canary and London Fancy. Bob has written many articles for Cage and Aviary Birds and was co-author with Peter Lander of the Popular British Birds in Aviculture series, which is still available.
  5. Breed selectively for pied greenfinches (see above). Unfortunately I know little about Dave Henderson. Some of his articles on ‘going-light’ and pedigree breeding have been published online and make interesting reading.
  6. Bob has confirmed to me that Dave Henderson’s hypothesis is correct.
  7. An allele is a gene with two or more variations. A bird inherits one allele from each parent.
  8. The variegation might be expressed as a single light claw, or a light feather hidden in the underflue.

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