Each bird selects objects to add to their bower based on personal preference. Sometimes it is based on color, sometimes it is based on organization and sometimes it is based on what they can steal from other bowers. Through color, sizes of collection and organization skills are attracted to particular males.
The key is that males are able to choose what they use for decorations vs. what they were born with.
Younger female bowerbirds prefer males that build more elaborate bowers.
Older female bowerbirds prefer males that perform more elaborate dances (Triveldi, 2004).
Bowerbirds are polygynous, so the male bowerbird who performs an elaborate dance in an elaborate bower will be more likely to be more successful at mating.
Triveldi, B. (2004, April 14). Bowerbirds Dance, Decorate to Suit Females' Changing Tastes. National Geographic News . Retrieved October 6, 2013, fromhttp://news.nationalgeographic.com/news/20