Ornithologists say the entirely white plumage of the bird is due to a condition known as leucism, which prevents the usual pigments from being deposited in its feathers.
Most birds with the mutation have some spots or patches of color in their feathers from other pigments, but the one seen around Nottinghamshire is unusual for being entirely white.
Leucistic birds are often far more vulnerable to predators because of their bright white plumage.
The BBC reports park managers in Nottinghamshire are urging birdwatchers to keep an eye out for this unusual blackbird when it returns in the spring, and sound the alarm should it come under threat.
Top photo: Notts County Counci
Bottom photo: File