Social Signaling

A book I received for Christmas got me interested in melanins in bird feathers. Melanins are pigments found in most organisms. Their chemistry is complex and their functions in many organisms are not understood. In birds they are responsible for the majority of black, brown and earth-toned colors. The scientific literature reports several reason birds evolved feathers containing melanins.

1. Resistance to mechanical damage: Melanins make feathers harder and thus more resistant to physical abrasion and mechanical damage. Stronger feathers that do not break influence flight. For this reason the tips of flight feathers which are exposed to heavy wear are often dark (ex. American white pelican [Pelecanus erythrorhynchos] and birds which move through abrasive vegetation or environments are also dark).

2. Protection from microbial degradation: Melanized feathers are more resistant to bacterial degradation than lighter feathers. This is seen in many sparrows which follow Gloger’s Rule (see “Gloger’s Rule” on 10-10-2016).  This ecogeographical rule states that species living in humid regions are usually darker in color than ones living under more arid conditions. Conditions in humid regions generally support bacterial growth and resultant feather damage more than dry habitats.

3. Crypsis (avoidance of observation or detection): The colors melanins impart to feathers and the resultant plumage patterns help birds blend into their environment, protecting them from predators. The killdeer (Charadrius vociferus) and her chick in the photograph are examples of this protective coloration.

4. Social signaling: Often the size and intensity of dark patches or other markings made by melanized feathers are used in courtship, dominance determination and other social interactions. For example, dark-eyed juncos (Junco hyemalis) with darker hoods and mantles are usually of higher social rank in wintering flocks.

5. Thermoregulation: Dark feathers are better at absorbing the sun’s radiation in cold weather and thus help keep birds warm in the winter.

6. Protection from UV radiation: Melanized feathers, particularly melanized contour feathers, are believed to help protect birds from the harmful effects of Ultra-violet rays. Melanin in the bird’s skin also shields against UV radiation.

Melanins in bird feathers have many functions. I recently learned of another benefit afforded by melanins in bird feathers. . . the topic of my next post.

The killdeer and her chick and the dark-eyed junco were photographed in our yard (Lookout CA, Modoc County). The American white pelican was flying over Baum Lake (Shasta County CA) while the song sparrow (Melospiza melodia) was in a thicket next to Baum Lake.

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1 Response to Melanins

  1. Lin Erickson says:

    Very informative.

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