My neighbors, Tim and Dianne, were excited! They had spotted an albino cardinal on their back fence. I am a Louisville Cardinal basketball fan and since they and every cardinal I have ever seen are bright red, I couldn’t wait to see a photo and here it is…
Something was bothering me about the “albino”. Albinos are supposed to have pink eyes and Tim’s had a black eye – so time to do research! Albinism, I discovered, is all or nothing. Pink eyes are a must and albinos are ALL white – not mostly white. Albinos in the wild are very rare in any species since they stand out and are easy prey, most die very young. In addition, their eyesight is very bad contributing to an inability to find food or avoid enemies. Tim’s cardinal was not an albino in the truest sense of the word but instead is a “leucistic” cardinal. Leucistics are still rare and it is a genetic defect but they retain some color and don’t have the eye issues so survivability is enhanced.
Leucism is a general term for the phenotype resulting from defects in pigment cell differentiation and/or migration from the neutral crest to skin, hair, or feathers during development. This results in either the entire surface (if all pigment cells fail to develop) or patches of body surface (if only a subset are defective) having a lack of cells capable of making pigment.
Since all pigment cell-types differentiate from the same multi-potent precursor cell-type, leucism can cause the reduction in all types of pigment. This is in contrast to albinism, for which leucism is often mistaken. Albinism results in the reduction of melanin production only, though the melanocyte is still present. Thus in species that have other pigment cell-types, for example xanthophores, albinos are not entirely white, but instead display a pale yellow color.
More common than a complete absence of pigment cells is localized or incomplete pigmentation, resulting in irregular patches of white on an animal that otherwise has normal coloring and patterning. This partial leucism is known as a “pied” or “piebald” effect; and the ratio of white to normal-colored skin can vary considerably not only between generations, but between different offspring from the same parents, and even between members of the same litter.
A further difference between albinism and leucism is in eye color.. Due to the lack of melanin production in both the retinal pigmented epithelium (RPE) and iris, those affected by albinism typically have red eyes due to the underlying blood vessels showing through. In contrast, most leucistic animals have normally colored eyes.
To add to the general confusion, here is a yellow cardinal.