Why do tinamous have such colorful, glossy eggs?

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Excellent question!

It does seem silly for a ground-nesting bird to have such brightly coloured eggs, as it should obviously make much them easier for predators to find.

However, it has been suggested that the eggs are brightly coloured so that other female tinamous can spot them easily - females tend to add their eggs to another bird's clutch rather than laying theirs in a separate spot, and they then leave a male guarding a large pile of eggs belonging to several females (and not all of them his!). Leaving eggs in greater numbers reduces the chances of a single female's eggs all being eaten, as predators are less likely to be able to eat all of the eggs in a large clutch.

There's an interesting paper on the subject here: http://onlinelibrary.wiley.com/doi/10.1 … C06.d01t03