jueves, 2 de enero de 2020

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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