We have completed maintenance on DiscoverMagazine.com and action may be required on your account. Learn More

Why Do Some Birds Lay Blue Eggs?

American Robins aren't the only bird that lays blue eggs.

Seriously, Science?
By Seriously Science
May 30, 2016 11:00 AMMay 19, 2020 4:26 AM
Blue Robin Eggs in Nest - Shutterstock
Robin eggs. (Credit: Andrea J Smith/Shutterstock)

Newsletter

Sign up for our email newsletter for the latest science news
 

While you might be most familiar with “robin’s egg blue”, many species of birds lay blue-colored eggs. Why might this have evolved? Although scientists can’t go back in time to observe the emergence of blue eggs, they can think carefully about which properties might be most different between blue and non-blue eggs — which is what these researchers did. They found that blue eggs absorb just the right amount of light to warm the egg, but not allow it to get too hot. Egg-cellent!

“The vibrant colors of many birds’ eggs, particularly those that are blue to blue-green, are extraordinary in that they are striking traits present in hundreds of species that have nevertheless eluded evolutionary functional explanation. We propose that egg pigmentation mediates a trade-off between two routes by which solar radiation can harm bird embryos: transmittance through the eggshell and overheating through absorbance. 

We quantitatively test four components of this hypothesis on variably colored eggs of the village weaverbird (Ploceus cucullatus) in a controlled light environment: (1) damaging ultraviolet radiation can transmit through bird eggshells, (2) infrared radiation at natural intensities can heat the interior of eggs, (3) more intense egg coloration decreases light transmittance (“pigment as parasol”), and (4) more intense egg coloration increases absorbance of light by the eggshell and heats the egg interior (“dark car effect”).

Results support all of these predictions. Thus, in sunlit nesting environments, less pigmentation will increase the detrimental effect of transmittance, but more pigmentation will increase the detrimental effect of absorbance. The optimal pigmentation level for a bird egg in a given light environment, all other things being equal, will depend on the balance between light transmittance and absorbance in relation to embryo fitness.”

1 free article left
Want More? Get unlimited access for as low as $1.99/month

Already a subscriber?

Register or Log In

1 free articleSubscribe
Discover Magazine Logo
Want more?

Keep reading for as low as $1.99!

Subscribe

Already a subscriber?

Register or Log In

More From Discover
Recommendations From Our Store
Shop Now
Stay Curious
Join
Our List

Sign up for our weekly science updates.

 
Subscribe
To The Magazine

Save up to 40% off the cover price when you subscribe to Discover magazine.

Copyright © 2024 Kalmbach Media Co.