Baby Blues.
Many species of birds lay blue-green eggs, but what the color signifies has stumped biologists. One theory is that it serves as a signal of quality to males, as the shell pigment, biliverdin, is expensive to produce.
To test whether blueness is an indicator of reproductive benefits, a team led by Juan Moreno, an ornithologist at the National Museum of Natural Sciences in Madrid, measured the color intensity of the eggs of pied flycatchers. The researchers also measured the amount of antibody proteins within each egg and the survival rate of the chicks.
The bluer the better, it turns out. Bluer eggs contained more maternal antibodies--the first line of immunological defense for freshly hatched chicks. Chicks from such eggs also were more likely to survive their first 2 weeks, the researchers reported online 15 March in Biology Letters. As a bonus, biologists can now use egg color as a quick guide to the health of such bird populations.
These results firm up the "signal theory" of egg color, says Lynn Siefferman, an ornithologist at Auburn University in Alabama. The next step, she says, is for researchers to artificially color eggs and see if males invest more care in bluer ones.
CREDIT: JUAN MORENO/MNCN
