It is very difficult to keep these beautiful birds as an aviary species. Because they have specific requirement i.e. heat and humidity. The temperature should be over 25 degree Celcius and the humidity should be quite high to keep and breed these living jewels in an aviary environment. As an ornithologist and aviculturist keeping and breeding this species is a challenge even for me.
I upload this footage to show the beak differences between individuals. It can be seen that one of the bird's beak is different than others as swollen at the base and convex cutting edges, and this bird's and another ones are bigger and thicker than the remaining.
According to an American study, the beak difference between individuals in this species, is not related sex, age or subspecies. On the other hand there is a book, written by C. S. Roselaar, named 'Songbirds of Turkey' is a very detailed study and in this book Roselaar represents a new Bullfinch subspecies (Pyrrhula pyrrhula paphlagoniae) based on the similar beak differences (and body measurements. But actually P.p. paphlagoniae's size is not so different from P. p. germanica).
Under this explanations, I kindly invite the ornithologists and anyone who has knowledge about genetical based individual differences and especially taxonomists (who have the knowledge of the subspecies recognition critteria) to discuss and share their opinions.
Murat Faik Özçelik