Why are birds' eggs colorful?

How do brood parasites, such as cuckoos, mimic the egg colors of their hosts. And when can host birds tell their own eggs apart from the foreign eggs in the nest?

HFSP Young Investigator Grant holders Mark Hauber, Matthew Shawkey, Tomas Grim and Geoffrey Waterhouse and colleagues
authored on Tue, 21 February 2017

A recently concluded HFSP Young Investigator Grant, awarded to team members from New Zealand, the USA, the UK, Belgium, and the Czech Republic, discovered that, although bird eggs are due to just two pigmentary compounds, some avian eggs incorporate nanostructural elements to cause their eggs to be glossy and iridescent. Brood parasitic birds, in turn, simply replicate the pigmentary composition of their host eggs to lay mimetic eggs that tricks the visual perception of some of their hosts to accept the parasitic eggs in the clutch. But those hosts that do reject foreign eggs, when faced with an array of model egg colors, rely on color-based categorization, rather than self/foreign dissimilarity assessment to recognize the intruder's egg in their nest. 

Overall, across its two funding cycles (the initial Young Investigator Grant awarded in 2007 was renewed for 3 years in 2012), the project produced over 50 team-authored publications, including works in the Proceedings of the Royal Society of London B, Interface Journal of the Royal Society, and Biology Letters, and brought together chemists, neuroscientists, behavioral ecologists, and evolutionary biologists for a truly intercontinental and interdisciplinary suite of studies.

For more on the latest findings by the group, recently published in Proceedings of the Royal Society B, see the news item on the Phys.org website

Reference

Egg discrimination along a gradient of natural variation in eggshell coloration. Daniel Hanley, Tomáš Grim, Branislav Igic, Peter Samaš, Analía V. López, Matthew D. Shawkey, Mark E. Hauber. Published 8 February 2017.DOI: 10.1098/rspb.2016.2592.

Pubmed link

A nanostructural basis for gloss of avian eggshells and How do complex, colorful traits evolve? - more frontier science from the team