As regular CFZ-watchers will know, for some time Corinna has been doing a column for Animals & Men and a regular segment on On The Track... particularly about out-of-place birds and rare vagrants. There seem to be more and more bird stories from all over the world hitting the news these days so, to make room for them all - and to give them all equal and worthy coverage - she has set up this new blog to cover all things feathery and Fortean.

Thursday, 2 June 2016

Biologists Solve Mystery of Blue-Green Bird Eggs

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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