Abstinence makes for bluer feet
Researchers of a Spanish and Mexican university discovered that when a male does not mate for a year, its feet have a more intense colour the next year. Thus the male becomes more interesting to the females.
In blue-footed boobies the males are also actively involved in breeding the eggs and taking care of the young. The researchers think that when a male does not have to take care of any young for a year, it is better able to recover and has more energy to make its feet nice and blue.