In the column “Since You Asked” in every issue of BirdWatching, Contributing Editor Julie Craves answers readers’ questions about birds and bird behavior. Here are two questions from our February 2016 issue:
I recently saw a catbird with a band across its tail. Is this an unusual color form? — Art Columbus, Toronto, Ontario
The condition isn’t too uncommon, but it’s not a plumage variation such as a color morph, in which a species can occur in one or more color forms. What you saw was a series of fault bars – pale sections caused by a reduction or absence in part of the feather structure. Fault bars are defects that are usually caused by a nutritional shortage or another form of stress while a feather is growing. They can happen to any feather but are most often visible on tail or wing feathers. When fault bars appear in adjacent feathers, forming a band, it means the feathers were growing simultaneously, then slowed and malformed at the same time. In most songbird species, this happens only when a bird is very young. Adult birds replace just a few feathers at a time, so fault bars appear staggered.
Why would a woodpecker peck on a stone wall? — Carmen Crane, Baltimore, Maryland
If the wall was porous, the bird may have been probing for small insects in holes and crevices. A more likely explanation is that the wall was limestone or a similar material that is high in calcium. Birds cannot store calcium in their bodies. During the nesting season, they seek out calcium sources to aid in eggshell formation and chicks’ bone development. Birds usually obtain calcium from grit, snail shells, millipedes, and other natural sources, but a stone wall may serve the same purpose.
About Julie Craves
Julie is supervisor of avian research at the Rouge River Bird Observatory at the University of Michigan Dearborn and a research associate at the university’s Environmental Interpretive Center. She writes about her research on the blog Net Results, and she maintains the website Coffee & Conservation, a thorough resource on where coffee comes from and its impact on wild birds.
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