Auk editor Mark Hauber featured in NYT article on tinamou eggs

[Fern Davies]

http://www.nytimes.com/2014/12/23/science/the-shy-drab-tinamou-has-a-stunning-palette-that-still-holds-more-mysteries-than-answers.html?ref=science

 

Dull brown Tinamous produce some of the most spectacular eggshells in the world, in colors like sky blue. lime green and rich chocolate and so glossy that they can reflect overhead trees and brush.

 

“Working with these eggs was, for me, like becoming an artist,” said Mark E. Hauber, an animal behaviorist at Hunter College and author ofThe Book of Eggs. “They are so unique and unusual that it was hard to take my eyes off them.”

To crack the structural secrets of the eggs’ ceramic appearance, Dr. Hauber and his colleagues first attained green, blue, light brown and dark brown eggs from four species of tinamou kept by the Bronx Zoo, the Dallas World Aquarium and a private breeder.

At first, the team hypothesized that tinamou eggs might possess a special pigment. But chemical analysis found pigments no different from those of other birds.

So the researchers turned to the eggs’ cuticle, or outside layer. They quantified its smoothness down to the nanometer scale and measured the shininess of the mirrorlike surface, finding that tinamou eggs are up to 14 times as glossy as the average chicken egg. A spectroscopy test also revealed that the blue eggs were iridescent (the green and brown eggs were too shiny for the spectrometer to accurately measure). Finally, the team dissolved the cuticle using an acidic solvent, and found that the gloss and iridescence disappeared, leaving it duller than a chicken egg, though still vibrantly colored.

Smoothness produced at the nanostructural scale gives the eggs their shine, the team concluded, and those same tiny structures are probably responsible for the iridescence. “Such an effect has not been previously documented for any bird egg,” said Branislav Igic, an ornithologist at the University of Akron, who led the study.

Why tinamous evolved such bright, glossy eggs is a mystery, but the authors suspect it may have something to do with mating behavior. Unlike most birds, male tinamous take sole responsibility for egg-incubating duties, and a single nest might contain eggs from several females. Eggs seem to act as a sexual attractant, much as gaudy feathers do for other species, suggesting that the bright color may have evolved to catch a female’s eye.

On the other hand, the females might produce brightly colored eggs to make sure the males continually guard the nest, which would otherwise be quickly spotted by predators. Or finally, the eggs’ gloss could just be a byproduct of defensive mechanisms that evolved to protect it from water or microbes, for example.