A.T., email.

This is a female. It is not uncommon for blackbirds – more often males – to have one or more white feathers. This seems to occur more often in blackbirds than in any other birds. However, I can’t recall having seen this in females before.

As can be seen from your photo, stray white feathers can appear on the head, body or tail. There was a “white-hooded” male at Ballarat’s Botanical Gardens several years ago. Others have merely one or two white tail or wing feathers.

It is probably caused by some sort of minor genetic defect. Your bird is building a nest, so it will be interesting to see if this trait occurs on any of its offspring.