Grey schizochroic Robin (Erithacus rubecula) in Doñana, December 2019
José Luís Anguita found an unusual bird at
La Rocina stream, Doñana, Huelva, Spain the last 28 December 2019. It recalled
a Robin (Erithacus rubecula) but it lacked its usual reddish bib and looked
overall greyish-bluish. Initially the observer went shocked when the found the
bird:
Lo encontré en el arroyo de La Rocina, Huelva, el
pasado 28 de Diciembre de 2019. Podrás imaginar el susto. .../...
The bird remained at its site from
28-30.12.2019. And beyond an aberration in a Robin coloration, he wondered if
those bluish tones may have something to deal with some kind of hybridization
with another species.
Indeed, as he pointed out regarding a previous observation of a bird in the UK this bird is a ‘Grey’ schizocroism mutation affecting one of the species
pigments, the phaeomelanin. And the bird is indeed a Robin (Erithacus rubecula).
As Van Grouw (2006) -excerpt below- stated in his clàssic reference
on colour aberrations (Not every white bird is an albino: Sense and nonsense
about colour aberrations in birds,Dutch Birding 28), this lack of reddish
tones are related to the lack of phaeomelanin which formation is genètic based.
Hence, a mutation – rare- causes these cold-looking birds:
Not every
reddish coloration is a result of carotenoids; for the orange-brown breast in
European Robin Erithacus rubecula are caused by a melanin.
Two
types of melanin are present in birds: eumelanin and phaeomelanin. In a high
concentration, phaeomelanin is responsible
for reddish-brown feathers,
The
melanin formation process is determined genetically. Any aberration in the
process has a potential influence on the colours of a bird.
Phaeomelanin
is responsible for red-brown pigments. The diferent shades of this pigment as
the human eyes see it from deep red-brown to yellowish-cream, also depend on
the concentration.
Schizochroism
Schizochroism
is defined as the absence of only one of both melanins. Two forms of
schizochroism can be distinguished,
Grey
Grey is
defined as a complete reduction of phaeomelanin (non-phaeomelanin
schizochroism). In this mutation, the plumage only contains the black/grey and
brown eumelanin. When phaeomelanin is absent (grey), only black-grey and dark
brown colours will be visible, the red-brown to yellowish-cream colours having
disappeared.
In any case, a very rare mutation and a very nice-looking bird, a Robin coming from the cold! All photos © José Luís Anguita.
Citation
Anguita, J.L. 2020. Grey schizochroic Robin (Erithacus rubecula) in Doñana, December 2019. Birds in Spain Blog. https://birdspain.blogspot.com/2020/01/grey-schizochroic-robin-erithacus.html
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