A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Are blue jays not really blue? Plus: has the copyright on "Happy Birthday" expired yet?

July 28, 2000

Dear Cecil:

Many years ago during an otherwise forgettable science class the teacher told us that "blue jays aren't really blue." Supposedly their blue color is not a result of pigment but rather an optical illusion produced by diffraction through the feathers or something. I spot blue jays from time to time and stare at them, hoping to see them as they really are, after the manner of Kipling's eponymous hero Kim, in training for the Great Game. However, it's not working. Tell me, Cecil, are blue jays not really blue?

This is one of those what-is-reality-type questions best debated over a six-pack, but in the interest of keeping things linear let's trim it down to size: Is blue jay blue produced by a surface optical effect rather than pigment? Answer: yes. In fact, blue and green pigments are virtually unknown in birds, having been found only in an African species known as the turaco. In other birds, including your jays, bluebirds, etc., the blue is merely a trick of the light, producing what ornithologists call a structural color or schemochrome. Grind up a blue feather — no blue. For that matter, hold a blue feather up to the light, so that you're seeing it by transmitted rather than reflected light, and you'll find the blue disappears.

For many years the standard explanation for blue jay blue was that it was produced by scattering, the same process that makes the sky blue. Blue jay feathers contain particles so small that they cause selective scattering (reflection in all directions) of the shorter wavelengths of light, which collectively appear blue. In the jay, the cells containing these microscopic particles are underlain by another cell layer containing the dark pigment melanin. The contrast of blue against a dark background makes the color stand out.

In parrots you've got the same basic structure, except that the blue-producing layer is overlain by a transparent yellow layer. Blue masked by yellow produces green. White feathers are also schemochromic. They look that way because they reflect all colors, but they contain no pigment and under certain conditions can be shown to be transparent.

Fine, you say. But is all of this really caused by scattering? Maybe not. Writing in the November 5, 1998, issue of Nature, Rick Prum, an ornithologist at the University of Kansas, argued that blue feathers don't look blue for the same reason the sky does, they look blue for the same reason oil slicks do. The phenomenon here is called interference or coherent scattering. Basically, as light bounces off the regularly spaced microscopic structure of the feather, it splits and then recombines. When it does so, all the wavelengths cancel out except blue, which intensifies.

So, which is it, scattering or interference? Rick makes a good case for the latter, but I'll let the boys fight it out. In the meantime, just remember that whatever virtues blue jays may have, they're not true blue.

Dear Cecil:

In your book The Straight Dope, you said the copyright on "Happy Birthday" was due to expire in 1996. Does this mean I can now sing this song at my kid's B-day without fear of being visited by the copyright cops?

Cecil replies:

Sure. Just don't pass the hat afterward. The copyright laws having been revised, the copyright on "Happy Birthday" now won't expire until 2011 — or at least so says Warner/Chappell Music Group, current owner of the song. But the restriction applies only to commercial performances. You can sing it for free to your heart's content.

To recap for those whose memory has faded since our original column on this subject in 1977(!), the music for the song was written in the 1890s by Mildred Hill, with the original lyric "Good Morning to You" by her sister Patty. As near as I can tell, the sisters didn't file for a copyright and many years later their song was stolen by a Tin Pan Alley shark, who published it with the lyric "Happy Birthday to You." The Hills prevailed in court and were granted a copyright in 1935.

According to ASCAP (the American Society of Composers, Authors and Publishers), which acts as a clearinghouse for music royalties, "Happy Birthday" was by far the most widely performed musical work of the 20th century (or perhaps more accurately, the most widely performed work still under copyright protection, and thus within ASCAP's purview). We asked Warner/Chappell what kind of royalties the song was bringing in — they said they'd get back to us. Personally I wish I could have written "Blue Suede Shoes," but I'd settle for Warner/Chappell's check.

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