Research has shown that the ‘blueness’ of a male boobies feet is a reliable indicator of their condition. If a male is unhealthy, weak or old it will generally not be as good at securing food as a healthy male, resulting in a reduced concentration of carotenoids and hence, duller feet. Conversely, having bright feet signifies that an individual is strong and healthy and can ‘afford’ to use more carotenoids for foot coloration (although it must be stated that this is not a conscious decision made by the bird).So it would appear that the blue feet which this charismatic species are so famous for are the result of a trade-off between immune function and signalling. Studies have even shown that foot colour reflects paternal contribution to raising offspring. Chicks raised by brighter-footed males growing faster than those raised by duller-footed males. With this taken into consideration it is no wonder why blue feet are so attractive!