Crest or no crest?
The difference is nothing more than the length of a bird's crown feathers
Contributed by David Allen Sibley
Published: January 1, 2009
 CONVERTIBLE CROWNS: Feathers on the crown of the Savannah Sparrow depicted three times at top aren't as long as those on the Northern Cardinal, but they can change the contour of its head just as dramatically.
Art by David Allen Sibley
Well, the difference between crested and not crested isn't that clear-cut. Many species can appear to be somewhat crested at least some of the time, and even truly crested birds can, at times, make their crests pretty inconspicuous.
No matter how a crest appears - clear-cut or not, raised or lowered - it is important to understand that crests are composed entirely of feathers.
There is no significant difference between the skulls of the Northern Cardinal and Rose-breasted Grosbeak, or those of the Steller's Jay and the scrub-jays, for example. As I tried to show in the illustrations reproduced above, the differences in head shape are simply the result of differences in the length of the crown feathers.
Feathers that make a true crest are unusually long. When they are raised up from the top of the cardinal's head, for example, they form a peak that is tall and conspicuous. When the same feathers are laid down more or less parallel to the skin, they follow the contour of the skull like "normal" feathers. The only evidence of a crest is a small tuft of feather tips sticking out at the back of the head.
We can see similar variations in the head shape of virtually any other species as the bird raises and lowers its head feathers. In the case of a Savannah Sparrow, the crown feathers are only slightly elongated, so they do not form a true crest, but shape still changes dramatically - from smooth and relatively flat when feathers are laid against the top of the head to "slightly crested" when feathers are raised to stand up from the top of the head.
The changing shape of the sparrow's head is controlled entirely by the angle of the feathers, in the same way that the Northern Cardinal raises and lowers its crest. The cardinal's head shape is different from the sparrow's only in that some of its crown feathers are longer than the sparrow's. |
David Allen Sibley is the author of The Sibley Guide to Birds, Sibley's Birding Basics, and Sibley guides to birds of eastern and western North America.
Read more by David Allen Sibley.
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