The handicap hypothesis states that extravagant features that are costly to produce and maintain are honest signals of mate quality. Males that are able to produce and maintain these traits have good genes are ideal choices for mates (Zahavi, 1975).
The Peacock's TailEdit
The mail peacock's tail or train makes up over 60% of it's body size. These tails consist of opulent, showy feathers that are energetically costly to produce and maintain. However, the longer the male's train and the higher the number of eyes, the more successful he is at mating (Petrie & Halliday, 1994). This supports the handicap principle. This tail is heavy, long, and cumbersome, making it difficult for the male to escape predation (Zahavi, 1975). However, females still select for a longer tail in their mates.
Petrie, M., & Halliday, T. (1994). Experimental and natural changes in the peacock's (Pavo cristatus) train can affect mating success. Behavioral Ecology and Sociobiology, 35(3), 213-217.
Zahavi, A., (1975) Mate selection: selection for a handicap. Journal of Theoretical Biology. 53: 205-14.