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Wesołowski T. 1987. Polygyny in three temperate forest Passerines (with a critical reevaluation of hypotheses for the evolution of polygyny). Acta Ornithologica 23: 273-302. 

During a four-year study carried out in primaeval stands of the Białowieża National Park (E Poland) a regular occurrence of polygyny in Phylloscopus sibilatrixPhylloscopus collybita and Troglodytes troglodytes was recorded. The polygynous males were usually bigamists, trigamy was exceptional. All females a polygynous male obtained settled in the same territory.The polygynous birds were recorded almost exclusively in optimal (= high-density) habitats. Proportion of polygynous males in these habitats varied considerably between years, ranging from 0 to 40%. Mating success of individual males varied among seasons as well. Primary and secondary females settled often at the same time or only 1-2 days apart. Production of young per female in polygynous groups was not lower than the production of females mated to monogamous males. The testability of polygyny threshold model is questioned. It is argued that current models dealing with female choice are insufficient to explain the evolution of polygyny. This is because the settling females have to make a whole series of decisions. they have not only to choose mates but also habitats and geographical areas in which to breed. Choices made on the latter levels may be as important as mate choice in deciding if polygyny will occur. Monopolization of access to females by males can result in the appearance of polygyny even if it is detrimental to females. A model showing how differences in female and male habitat distribution (ideal free and ideal dominance respectively) can lead to locally skewed sex ratios and occurrence of facultative polygyny is presented. It is stressed that in order to explain the evolution of the resource defence polygyny one has to study simultaneously reproductive options available both to the females and to the males, as well as a whole set of ecological factors influencing the monopolizability of habitats by the males and costs of polygyny to the females.