Territoriality in breeding Whitethroats were examined on colour-ringed individuals in two areas located in different geographical regions: Low Volga and Caucasus coast of the Black Sea. In the Caucasus region 29% of males were polyterritorial (6% — bigynous) whereas in the Volga region no cases of males polyterritoriality nor bigyny were observed. Literature reveals that in regions, where polygyny in the Whitethroat was observed, the breeding period is short and the species has only one breeding cycle in a season. In the areas where the breeding period is long, bigyny has not been found, but cases of double- broodness was observed. Author suggests that bigyny in the Whitethroat evolved as a response to the short breeding season, which does not allow males to have two successive broods in a season. The only way to increase their reproductive success is to establish a second territory immediately after the first female starts to lay.
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