Reid, ML & PJ Weatherhead. 1990. Mate-choice criteria of Ipswich sparrows: the importance of variability. Animal Behaviour, 40: 538-544.

Summary (AGH): Many of the most interesting traits of songbirds, such as their bright plumage and complex songs, have evolved for more effective competition for mates. Breeding success of males mainly depends on whether they can attract females, whereas breeding success of females mainly depends on the quality of the breeding situation they settle on in the spring. This study showed that females settle on territories depending on which aspect of the breeding situation varies the most. In a year when territories were relatively similar in size, habitat, and other features, but males varied in features such as size and song rate, females settled sooner with more vigorous males, whereas in a year when territories varied but males were similar, they settled sooner on higher quality territories, without regard to male quality. The study is an interesting example of how what drives the ecology and evolution of a population can vary from one year to the next, depending largely on weather.