Question of the month

The pigments don’t lie

I was taking a look through the Discovery Centre and noticed the interesting colours of the ocean birds’ feet (and their foot/beak colour combos!). Is there a reason why they have the various colouring that they do?

Answer

A breeding Roseate Tern (Sterna dougallii) showing the normally black legs and beak in bright red breeding colouration. The black cap is usually restricted to a half cap behind the eye when not breeding. Photo © Queensland Museum, Gary Cranitch.
A Great Egret (Ardea alba [modesta]) in breeding colours. The non-breeding yellow beak and facial skin change to a black beak and blue-green facial skin. The typical dark base to the legs is also brighter pink. Photo © Chris Burwell.
A proud Red-footed Booby (Sula sula) showing its blue bill and striking red feet. Photo © Will Goulding.

The colour of the feet and legs, bills and facial skin can be an indication of breeding status in many seabird species. These parts can change to brighter or bolder colours during the breeding season and as you have noticed, many of the seabirds on display are presented in this colourful state.

Some good examples of this are provided by many of the tern species, which get brighter coloured bills and legs, and change the colours of their feathers (e.g., acquire solid black caps) when breeding. However, it is not just seabirds that make such changes with breeding status. Some of the egrets, herons, ibis and spoonbills also undergo bill, skin and plumage changes with breeding. Similarly, many waterfowl (grebes and ducks) and shorebirds (waders) change colour during the breeding season, but these changes are mostly in their plumage.

Several booby species (species of Sula) have particularly colourful feet, bills and facial skin when mature. In the Brown Booby (Sula leucogaster) and Abbott’s Booby (Papasula abbotti), males and females differ in the colour of their bills. In more colourful species such as the Red-footed Booby (Sula sula), however, males and females both have conspicuous red feet, pink skin and blue bills. This species is colourful all year, but the intensity of these coloured areas generally increases with breeding.

Apart from indicating breeding status or sex, do the colourful parts have any other function?

These colours are generally considered to play a role as “honest signals”, meaning that brighter or stronger colours are a good indication of the highest-quality mates. In other words, a greater intensity in these coloured parts can indicate individuals in better condition, making them more desirable partners. This is because the pigments responsible for these colours (e.g., carotenoids or melanin) can require lots of energy and nutrients to gather, produce or maintain. This means that coloured parts can give a potential partner an indication of things like the other bird’s age, health status, breeding stage and ability to successfully find and provide resources. Given the importance of these coloured parts as indicators, they commonly feature prominently in breeding or courtship displays. Some good examples of this are provided by the courtship dances of Red-footed Boobies or the more renowned Blue-footed Boobies (Sula nebouxii; found in the eastern Pacific), which both prominently feature their feet.

Given all this, it can be said that beauty really is skin deep for many seabird species.

Want to know more? Our Discovery Centre is a free service open seven days per week, with experts ready to answer your questions. You can phone, write, contact us via our website or pop in. If we don’t know the answer, we will try to find it for you.

 

 

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