Home to the Galapagos Islands off the coast of South America; blue-footed boobies have really made a name for themselves with their bright blue feet. Not only are their famous footsies good for standing on but they’re useful too in attracting mates, and males perform elegant foot flaps for any watching females to show just how splendidly blue they are.

However, with great colour comes great responsibility and exactly how bright, dull, blue or bluey-green their webbed walkers are can have great repercussions on their young – we’re talking life or death here people. So what the boob is going on? Why do these birds have such extravagantly blue feet?

It’s not easy being blue

No really, it isn’t. The chemical compounds that make a blue-footed booby blue footed, cannot be synthesised by the bird alone and must instead be obtained through food. The better a male’s diet (lots of fish, few doughnuts), the more striking his feet become. A booby’s feet are therefore one huge glaring sign as to who is fitter and consequently who will make a better father to a female’s offspring.

But a male isn’t safe from judgement once he finds a female. Oh no, as soon as his feet start to become duller the female very quickly reacts by putting less effort into producing her eggs. Scientists who took male boobies and painted their feet a duller blue saw their female partners lay significantly smaller eggs just days later.

The females know that if the male isn’t in good condition he’s not going to be as helpful raising their chicks and consequently those chicks will have a decreased chance of survival. Their solution? The female instead lays one large egg and one smaller egg, and in doing so helps to ensure that the first chick will be strong enough to kill the second.

It’s especially not easy being the second egg

That’s right, blue footed boobies (had they a human like conscience) might also be feeling a little blue because of the seemingly cruel way they make it in this world. Boobies often undergo brood reduction, where one sibling kills its others.

If conditions aren’t favourable, as predicted by the male’s dull blue feet, booby parents are happy to let their strongest chick kill its siblings to save on resources – and the eldest chick is all too happy to do so because eliminating its siblings means more food for it.

With great colour, comes great responsibility

So there’s much more to blue than meets the eye – if you’re a blue-footed booby that is. The colour of a male’s feet are a huge indicator of his health and females use this information to decide if all chicks stand a chance at surviving or if there’s going to be one big ol’ fight to the death. It’s a harsh reality, but in their bright blue shiny socks, boy those boobies are wearing it well.

---

References:

Mora, A. N. D. L., Drummond, H., & Wingfield, J. C. (1996). Hormonal correlates of dominance and starvation‐induced aggression in chicks of the blue‐footed booby. Ethology, 102(5), 748-761.

Velando, A. (2002). Experimental manipulation of maternal effort produces differential effects in sons and daughters: implications for adaptive sex ratios in the blue-footed booby. Behavioral Ecology, 13(4), 443-449.

Velando, A., Beamonte-Barrientos, R., & Torres, R. (2006). Pigment-based skin colour in the blue-footed booby: an honest signal of current condition used by females to adjust reproductive investment. Oecologia, 149(3), 535-542.