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

Abstract

In many species, territory ownership is a prerequisite for reproduction; consequently, factors that affect success in territory acquisition can have a large impact on fitness. When competing for territories, some individuals may have an advantage if, for example, they are phenotypically superior or more familiar with the site than others. The relative importance of the many factors involved in territory acquisition is, at present, unclear. We studied patterns of natural territory acquisition in a closed and saturated population of Seychelles warblers. Furthermore, by removing breeders, we experimentally investigated the relative importance, to territory acquisition, of a range of factors and assessed whether this differed between the sexes. In both sexes, the main route to natural territory acquisition was to disperse from the natal territory to immediately claim a vacant dominant position. Males were older than females when acquiring a territory for the first time. In the removal experiment, for both sexes, the proximity of an individual's natal territory to a vacant dominant position was positively related to the individual's chance of claiming the vacancy. Older males were more likely to gain an experimental vacant dominant position than were young males, whereas age did not affect territory acquisition in females. In the Seychelles warbler, the degree of intrasexual competition for territory ownership may be stronger for males than for females because territory ownership is a prerequisite for male reproduction, whereas females can reproduce on their natal territory. In such competition, young males subsequently lose out to older ones.

Seychelles warblers: Complexities of the helping paradox

“…Given the importance of territory ownership, competition over breeder vacancies may be more intense for males than for females. h is is supported by the fact that experimentally created male vacancies were occupied faster than female vacancies (Eikenaar et al 2009 ).…”

Changes in the acoustic environment alter the foraging and sheltering behaviour of the cichlid Amititlania nigrofasciata

“…However, tank experiments mimic common ecological circumstances faced by many species where individuals cannot avoid noise polluted areas. For example, species that either inhabit confined habitats, defend territories (Bruintjes and Radford, 2013), or which rely upon seasonal, or patchy resources may be among those affected (Eikenaar et al, 2009). These constraints can hinder avoidance of noise, requiring individuals to adjust their behaviour within their ecological and physical boundaries.…”

Sex biased natal dispersal is not a fixed trait in a stable population of Seychelles warblers

“…In the Seychelles warbler, the majority of male and female offspring remains in the natal territory and disperse only when they are able to claim a vacant dominant breeder position (Eikenaar et al, 2009). An alternative explanation for the change in dispersal observed in this study, therefore, could be that, over time, competition for dominant breeder positions weakened for females or became more intense for males.…”

“…First, because the number of competitors per breeder vacancy did not change, in later years of the study more females left their natal territory without immediately claiming a dominant breeder vacancy. From 1985-1990 none of the female subordinates were observed as floaters (Komdeur, 1991), whereas from 1995-2005, 16% of female subordinates were seen floating at some stage before they settled as a dominant breeder (Eikenaar et al, 2009). Secondly, because delayed dispersal allows for offspring to help their parents (Ekman et al, 2004) the earlier dispersal of female offspring in later years meant that fewer were available to help their parents.…”