Here’s a Leucistic American Robin photo we took fairly recently. It’s possible you may have seen one of these birds, but it was a first for us at the time. I definitely am not a bird or genetics expert, but according to a variety of online sources, leucism describes defects in pigment cells caused during a bird’s development, which prevents pigments from reaching some or sometimes all of a bird’s feathers. The degree of leucism varies with a bird’s genetic makeup. The skin and eyes remain their normal pigment and color. You will see white splotches on its head or back.
We also have a photo of a Canadian goose that appears to be leucistic. We saw both of these at separate times while on our photo walks at a local wildlife refuge.