May 30, 2016 by Editors
Blue-green egg color shields bird
embryos from harmful sunlight, according to Dr. David Lahti from the City
University of New York and Dr. Dan Ardia from Franklin & Marshall College.
The authors tested the hypothesis
that pigmentation might help an egg strike a balance between two opposing and
potentially damaging effects of the Sun: light transmission into light-colored
eggs, and heating up of dark-colored eggs.
“We quantitatively test four
components of this hypothesis,” they wrote in a paper published in the May
issue of The American Naturalist, “on variably colored eggs of the village weaverbird (Ploceus cucullatus) in a
controlled light environment:
(i) damaging ultraviolet (UV)
radiation can transmit through bird eggshells;
(ii) infrared (IR) radiation at
natural intensities can heat the interior of eggs;
(iii) more intense egg coloration
decreases light transmittance (pigment as parasol);
(iv) more intense egg coloration
increases absorbance of light by the eggshell and heats the egg interior (dark
car effect).”
As predicted, more intensely blue
eggshells shielded the interior from light, including dangerous UV radiation.
But more intense color also
caused eggs to absorb more light and heat up, which can be even more dangerous
in brighter environments.
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