Hot as shell: birds in cooler climates lay darker eggs to keep their embryos warm

Zorra

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Birds lay eggs with a huge variety of colours and patterns, from immaculate white to a range of blue-greens and reddish browns.

The need to conceal eggs from predators is one factor that gives rise to all kinds of camouflaged and hard-to-spot appearances.

Research - Today - Nature - Ecology - Evolution

Yet our research, published today in Nature Ecology & Evolution, shows that climate is even more important.

Dark colours play a crucial role in regulating temperatures in many biological systems. This is particularly common for animals like reptiles, which rely on environmental sources of heat to keep themselves warm.

Darker - Heat - Sunlight - Animals - Colours

Darker colours absorb more heat from sunlight, and animals with these colours are more commonly found in colder climates with less sunlight. This broad pattern is known as Bogert's rule.

Birds' eggs are useful for studying this pattern because the developing embryo can only survive in a narrow range of temperatures. But eggs cannot regulate their own temperature and, in most cases, the parent does it by sitting atop the clutch of eggs.

Colder - Environments - Risk - Predators - Risk

In colder environments, where the risk of predators is lower and the risk of chilling in cold temperatures is greater, parents spend less time away from the nest.

We predicted that if eggshell...

(Excerpt) Read more at: phys.org

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