Experimental evaluation of sex differences in territory acquisition in a cooperatively breeding bird

In many species, territory ownership is a prerequisite for reproduction;consequently, factors that affect success in territory acquisitioncan have a large impact on fitness. When competing for territories,some individuals may have an advantage if, for example, theyare phenotypically superior or more familiar with the site thanothers. The relative importance of the many factors involvedin territory acquisition is, at present, unclear. We studiedpatterns of natural territory acquisition in a closed and saturatedpopulation of Seychelles warblers. Furthermore, by removingbreeders, we experimentally investigated the relative importance,to territory acquisition, of a range of factors and assessedwhether this differed between the sexes. In both sexes, themain route to natural territory acquisition was to dispersefrom the natal territory to immediately claim a vacant dominantposition. Males were older than females when acquiring a territoryfor the first time. In the removal experiment, for both sexes,the proximity of an individual's natal territory to a vacantdominant position was positively related to the individual'schance of claiming the vacancy. Older males were more likelyto gain an experimental vacant dominant position than were youngmales, whereas age did not affect territory acquisition in females.In the Seychelles warbler, the degree of intrasexual competitionfor territory ownership may be stronger for males than for femalesbecause territory ownership is a prerequisite for male reproduction,whereas females can reproduce on their natal territory. In suchcompetition, young males subsequently lose out to older ones.