Female birds sacrifice health to create more colourful eggs

From Nature:

Great artists are said to pour all their energies onto the canvas, leaving them exhausted after a flurry of creativity. Now, researchers have found that female birds make a similar sacrifice when colouring their eggs, creating vivid hues at the expense of their health. The blue in many birds' eggs comes from the compound biliverdin, a breakdown product of the heme unit in haemoglobin, which circulates freely in the blood. But biliverdin is not just a pigment, it is also an antioxidant used by the body to prevent cellular damage.

Previous research has proven that when females lay vibrant blue eggs, their partners are more likely to stick around and help rear the young. So researchers speculated that because the blue comes from an antioxidant, it is a signal to males of the female's health status. Some scientists have argued that the female is making a dangerous trade-off, giving up resources needed to sustain her health to convince her partner that her offspring are worth looking after. 

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