Pairing Systems and Site Tenacity of the Willow Warbler Phylloscopus trochilus in Southern England

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Abstract
A population of willow warblers P. trochilus, which were color-ringed for individual recognition, were studied in a 46.5-ha area of mixed scrub in 1976-1981. Adults of both sexes returned not only to the study area but also to their former territories. Returns of juveniles were low but were appreciably higher for males than females. Territories were not static throughout the breeding season. In 1 yr, especially, a high turnover of territorial males was seen. Some males held 2 territories almost simultaneously; these males usually, though not always, succeeded in mating with 2 females. Six males managed to attract 2 mates within 1 territory. Some males in the study population apparently failed to obtain mates. In every year, additional males colonized the area very late in the breeding season.