Thursday, March 29, 2012

Melanistic or Dark Morph?

One day while at the World Bird Sanctuary I was looking at the beautiful coloration of one of our dark morph Augur Buzzards, and it got me to wondering. 
 Keeoo - Our beautiful dark morph Augur Buzzard
Normal Augur Buzzards are a slate grey on their backs with some speckling, and have white chests and bellies.  The dark morphs have a more overall black plumage.  While standing there I found myself wondering what the difference is between true melanism and a dark morph.
I found, through researching many books and websites, that true melanism is actually very, very rare.  It is a genetic mutation that causes the bird to have excess amounts of melanin in its feathers, which causes them to be very dark.  Melanism is generally accepted to be hereditary, but there is not enough scientific evidence to determine if it is or is not hereditary. 

When a species of bird has a regular color morph that has a slight degree of melanism it is not considered true melanism, but just a dark morph.  Eyes, feet, legs and beak color are not altered by melanism, which can assist in identifying a bird that has true melanism. 

According to some studies it is thought that melanistic animals may eventually one day be more common than non-melanistic animals.  Studies in cats and other animals have shown that melanistic animals have stronger immune systems and are much more resilient to disease than their normally colored counterparts.  It is believed that this trait is true in birds also.
In cold climate environments dark morphed and melanistic birds have an easier time absorbing some of the sun’s solar energy to help them regulate their body temperature, so they don’t have to use as much of their own energy.  Excess amounts of melanin in feathers, however, has also proven to make the feathers slightly weaker, making them more prone to breaking, and also renders feathers less flexible than they should be.
In the wild, dark morph Augur Buzzards are believed to account for about ten percent of Augur Buzzards.  In some areas this increases to about fifty percent of the population.  In the eastern part of the Augur Buzzard range there seems to be a much higher population of dark morphs.

The next time you visit the World Bird Sanctuary be sure to look for our dark morph Augur Buzzard, Keeoo, in the weathering area behind the Environmental Education Center (EEC).  Unless she is performing in an educational program with members of our staff, this is where she spends most days.  

If you do not live in the St. Louis area, we have two other Augur Buzzards—Sam, a dark morph, who will be flying in our Milwaukee Zoo show starting May 26, and Oracle, a normal morph, who will be flying at Stone Zoo in Boston beginning May 1. 

If you live or are vacationing in the Milwaukee or Boston area this summer come out and visit us at these two popular venues and be sure to look for Sam or Oracle

Submitted by Mike Cerutti, World Bird Sanctuary Naturalist/Trainer


Anonymous said...

Is it possible for a Snowy Owl (Bubo scandiacus) to show signs of melanism in feather pigmentation? I have never heard of there being a melanistic Snowy Owl, but this question has been like a bur stuck in my pinfeathers for half a year now. Any thoughts?

Photog said...

According to Jeff Meshach, Director of World Bird Sanctuary, "I guess melanism or albinism could happen to any living thing. For a Snowy Owl to be dark...bird would probably not survive long because of camouflage problems. Take Casper (an albino Great Horned Owl who lived at the World Bird Sanctuary for many years)...the only reason she survived was because a person found her on the ground, pretty close to death from starvation. Depends on the species, but either of the extremes usually don't last very long."