National Geographic : 2009 Jul
W ILDLIFE PHOTO: JOEL SARTORE AT UNIVERSITY OF NEBRASKA STATE MUSEUM Exterior Design When it comes to the art of egg decoration, Mother Nature is the original master. The patterns and lines that adorn many eggs---like those of murres, grackles, and jacanas---are positively calligraphic. These mark- ings, which get their pigment from bile acids and broken-down red blood cells, are applied during the tail end of the 20 hours during which the egg is in the shell-gland region of the oviduct. A shell that emerges encircled with wispy streaks (above) means the egg rotated while the inking occurred. Such surface flourishes serve two practical purposes, offering camouflage from predators and identification for colony-dwelling birds trying to spot their own. Another distinction, says wildlife ecologist Linnea Hall: No other animals on Earth mark their eggs. Now that's original artwork. ---Catherine L. Barker In utero motion created the elegant scrawl on the grape-size shell of this great-tailed grackle egg.