Compendium-Canaries, Volume 3

Special anatomy and genetics

The Skeleton

We find a changed physique in all domestic breeds, which can no longer be compared to the wild form. The physique of many canary breeds has also changed, as nature made this possible. Man has gratefully accepted these gifts of nature and further developed them according to his will.

Picture 2: Skeletons in comparison. Left: Colour canary; right: Figure canary (photos: Norbert E. W. Schramm)

As can easily be seen from the pictures of the skeletons, the figure canaries have the same bone structure, only their position is different. In most carduelids, the cervical spine is curved in an s-shape when at rest, forming the relatively short neck. Figure canaries can stretch the cervical spine, which has no more vertebrae than "normal" canaries, forward.

The muscles and tendons involved make this possible. The same applies to the upper and lower legs as well as the tibiotarsus, which are at altered angles to each other.

In a comparative study, 33 Figure and Frisé canaries of the breeds Bossu Belge, Frisé du Sud and Gibber Italicus were examined. The research team found that the Gibber Italicus and Frisé du Sud had eight instead of seven pairs of ribs. The number of cervical vertebrae was unchanged, but the length of the vertebrae was slightly longer (± 0.03 mm) in the Frisé du Sud. The extent to which these changes could lead to health problems, especially as the birds age, requires further investigation.6 However, breeders of these breeds cannot detect any age-related problems.

Causes and inheritance of feathered frills

A feather consists of - very roughly - of the visible feather and the feather follicle located in the skin. The feather grows out of the skin at a very shallow angle in normally feathered birds. In feathers that form frills, this angle is greater. In addition, the feather follicles can form whirls in certain parts of the body.

Some authors assume that the outside of the feathers grows faster or has larger feather cells than the inside of the feathers. This would result in a curved and bent feather. Accordingly, feather frills are caused by a changed distribution of the horn substances.

Picture 3: Position of the feather exit in feathers of frills and in normal feathers (modified drawing by Rita Reiser; www.wissen.de/lexikon/feder-zoologie).

According to another theory, the shape of the feather exit hole determines whether the feather grows out in a curved shape or not. On the other hand, most body feathers in all birds are slightly curved. It is certain that muscles in the skin make the frills appear or not.

In cold temperatures, when birds are sleeping or even dead, this muscle work is restricted or no longer present. Frills are then no longer recognisable.

In 2009, researchers found that mutations of the TCHH gene in humans affect hair structure. This gene encodes the trichohyalin protein, which affects the inner hair root sheath cells of the hair follicles.7 It is possible that there is a similar connection in birds.

What is certain, however, is that the feathered frills are obviously due to one or more mutations and are accompanied by an elongation of the feathers. The feathering frills trait is inherited independently of sex and is incompletely dominant, with variable trait development.

The lengthening of the feathers also results in the claws also growing longer. Constantly changing growth directions then lead to twisted claws, the so-called "corkscrew claws". These cannot wear down sufficiently and so there is an increased risk of injury from getting caught in branches or nesting material. Frequent shortening of the claws is therefore urgently required!

Causes and inheritance of feather crest

The crest is a particularly characteristic headdress of the crested posture canary. "The crest is caused by the fact that the follicles of the crest feathers do not cover each other from the root of the beak like a roof tile but are arranged in a whirl around a point located on the crown." 8

Starting from a central point, the feathers fall in all directions and cover the entire head plate. "The modified embedding of the follicles in the skin shows yet another recurring feature, by which it can already be recognised in the very young bird whether it will later carry a crest or not. The nape of the neck is featherless. In a fully feathered bird with a well-developed crest, this naked area is of course not visible because the extended crest feathers lie over it. But if you bend the bird's head forward, you can notice this bald spot on any crested bird. If the crest is poorly developed, the bald spot is more or less visible..."9

CHARLES BENEDICT DAVENPORT (1866 to 1944) already established that the crested trait is subject to an autosomal (non-sex-linked) and dominant inheritance.10 According to Mendel's rules of inheritance, which were already known at that time, the majority of young birds from a mating of crested bird with crested bird would have to wear a crest. However, this is not the case.

Hans Duncker carried out a large number of different mating, evaluated them statistically and finally found that 25 % of the young birds from a crested x crested mating do not hatch or die shortly afterwards.

The allele H (crested) is inherited non-sex-linked and incomplete dominant opposite to H+ (non-cap - smooth head).

There has been much speculation about the cause of this lethal effect in two-factor crested birds. Suspicions that serious cranial and brain changes occur could not be confirmed by scientific studies.11

Thus, crested breeding can only be carried out with single-factor crested birds, as two-factor crested birds do not reach breeding maturity. The mating of two single-factor crested birds produces approx. 25 % dead young birds, so that the number of born young birds is clearly reduced. Furthermore, the quality of the crests from such a mating does not improve, but rather deteriorates.

Picture 4: Position of the feather follicles in a young crested bird about 3 days old (photo: H. Duncker).

One should therefore always mate a crested bird with a smooth-headed partner. Whether the male or the female wears a crest is irrelevant. From such a mating - according to the inheritance rule - half of the offspring should wear a crest, the other half are crestless. However, Duncker already found out that this ratio is not exactly correct. He achieved only 47 % crested birds and 53 % smooth-headed. In my breeding the ratio of 40 : 60 was even more unfavourable with regard to the crested offspring.12 The mutated gene H must therefore also have a damaging effect on a very small proportion of the expected single-factor crested birds.

This inheritance applies to all canaries with a crest!

Variegated canaries

One of the first mutations to occur in animals is piebalds. which is called "variegation" by bird breeders. This means that in some parts of the body hair or feathers have no melanin. This partial lightening of the coat or feathers has always interested animal breeders. Thus, there are many breeds of domestic animals that are very familiar to us as piebald animals, such as black-coloured cows, piebald horses, rabbits or cats. In the birds we breed, variegation has appeared as the first mutation, think of the Bengalese finch (Lonchura striata domestica), the Java sparrow (Padda oryzivora), the zebra finch (Taeniopygia castanotis), the budgie and many other species. The canary is also very popular as a piebald bird. It stands to reason that all piebald species are the same phenomenon. British breeders refer to pied canaries as "variegated canaries".

How does piebald develop?

Already in an early embryonic stage (neurula) the still colourless melanin cells (melanoblast) are formed. These melanoblasts will later produce melanin. They are then called melanin cells (melanocytes). During further embryonic development, these melanoblasts migrate from the neural crest to the body regions and organs to be coloured with melanin (skin,...