Abstract
In 1977 and 1978, respectively, 3 and 4 territorial willow warbler males were removed with mist-nets in a subalpine birch woodland in Ammarnas, Swedish Lapland. Each year 1 new male established a territory in the vacated area. The surrounding males enlarged their territories slightly but not enough to fill up all of the emptied area. In control areas no changes occurred. It is concluded that territorial behavior of the stationary males exclude some males of the same species from establishing territories. The new males probably failed to get breeding partners and it is thereby possible that the reproductive output of the population was not affected by the exclusion of some males from breeding.

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