Many bird species raise only one brood per year because of a narrow period of suitable environmental conditions which prohibits multiple breeding attempts(Evans den& Stutchbury 199 Others raise multiple broods per breeding season(Verhulst et al. 1997) and the total seasonal fecundity for these species depends on the number of breeding attempts(Geupel& DeSante 1990), One of the principal determinants of multiple broods is the duration of the breeding season, which is often directly related to the abundance and availability of food(Holmes et al. 1992, Morrison 1998)