The common blackbird - Turdus merula - Leucism
This bird baffled me for some time until I happened upon the article below. These birds were introduced to Australia in the 1850's.
Plumage coloration in birds is mainly the result of the deposition of pigments in the feathers (Fox and Vevers 1960). The most important pigments in bird coloration are carotenoids (red and yellow coloration) and melanins (brown and black coloration) (McGraw 2005, 2005b). Disturbances in the deposition of pigments produce chromatic aberrations (van Grouw 2013). The most common of these aberrations, mostly associated with melanin-based pigmentation, is leucism or partial albinism (Guay et al. 2012), the total or partial lack of melanins in the feathers. Leucism is characterized by having white patches (in the most common cases only in the feathers) but normal coloration in some parts of the body (i.e. have normal-colored eyes, bill, skin and feet) (Guay et al. 2012).
https://onlinelibrary.wiley.com/doi/full/10.1111/jav.01778
The Common Blackbird is a species of true thrush. It is also called Eurasian Blackbird, or simply Blackbird, where this does not lead to confusion with a similar-looking local species. It breeds in Europe, Asia, and North Africa, and has been introduced to Australia and New Zealand.
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