This week we’re going to meet a rare bird and learn what made her so unique. Warning: science content ahead!
Both birds in our collage photo are juvenile pileated woodpeckers who were born in 2015 (they may or may not be siblings). The one on the right is a female; the one on the left is a male. However, the difference in their sex isn’t what accounts for their difference in color.
The male shows the typical black, white and red coloration of a pileated (which you may recall from past “Crawlies”). The female – we’ll call her Lady Jane Gray – shows a pale coloration called “Hypomelanism” which is the abnormal reduction of melanin concentration from the plumage, skin, eyes or all three areas.
Other terms for hypomelanism include leucism, albinism, partial albinism, imperfect albinism, dilute albinism, dilution, dilutism, ghosting, paling, isabellism and isabellinism (apparently “isabell” is a dark color).
Most often pale forms of birds are referred to as “dilute”.
First, let’s talk about how birds get their feather colors. Primarily they get their colors from pigments. There are two types: melanins and carotenoids. Melanins create black, brown, rufous, gray and buff colors. Carotenoids create yellow, orange and red colors.
As we’ve also discussed in past “Crawlies,” some feathers, like blue jay feathers and the refractive feathers on hummingbirds, have structural colors too (refracted light); but they still need melanin as the base for that structural color.
Lady Jane Gray is gray because she inherited her dilute gene from her father. How do we know this? Because females always inherit their dilute allele from their fathers, and they always pass a copy to their sons.
Fun fact: The recessive dilute gene only affects melanin, so the racy red head feathers on Lady Jane are as vibrant as those on the darker male, because they get their color from the unaffected carotenoids.
Can hypomelanism cause health/longevity problems? Yes, and no. To some degree, it depends on the species of bird. In chickens it has been shown to cause delayed early growth. However, in an isolated population of magpies in Alberta, Canada, it has persisted since the 1940s.
Vibrancy of color is a factor for some bird species when selecting mates. For example, paler purple finch males will be chosen last as mates by females. That said, with finch color vibrancy is directly linked to diet (as it’s carotenoid color), so paler males are viewed as being less healthy e.g. having a poorer diet.
Hypomelanism is so rare in pileated woodpeckers, there is no way to know if Lady Jane had any problems finding a mate.
Feathers with less melanin are also less structurally sound, so that could put Lady Jane at a slight foraging disadvantage as you can see; they use their tail feathers for stability/balance while drilling for bugs in trees.
Finally, if hypomelanism affects a bird’s eyes, it may also negatively affect their vision. Lady Jane’s eyes are blue, but that may just be because she was still young (many woodpeckers have blue eyes when they hatch, then the eyes darken to golden or brown hues).
The oldest known pileated woodpecker lived almost 13 years, so we can hope Lady Jane is still out there living her best life as the Gray Ghost of the Rogue.
Special thanks to Prof. Janet E. Hill University of Saskatchewan for research help.