How do Southern House Wrens Troglodytes aedon musculus achieve polygyny? An experimental approach

Abstract

I designed two experiments to evaluate how polygyny is achieved in Southern House Wrens (Troglodytes aedon musculus) breeding in a south-temperate population. In the first experiment, I manipulated territory attractiveness by adding high quality nesting sites (nest-boxes) to 50% of monogamous territories (n = 24) and evaluated if males can attract a second female when defending high quality resources. In the second experiment, I simulated high male mortality early in the breeding season by removing 30 territorial males in plots where wrens had been breeding in nest-boxes (n = 47 territories). The first experiment did not induce polygyny: although females switched from breeding in tree cavities to nest-boxes when boxes were erected on their territory, none of the neighbouring females who did not receive a box moved to breed as a secondary female. The male removal experiment did induce polygyny: of 21 experimentally widowed females, 38% bred as secondary females of neighboring males—who expanded their territories in the absence of a defending male—and accepted polygyny even in the presence of neighbouring territories held by bachelor males. Secondary females mated to polygynous males were rarely helped by the male while feeding nestlings, but primary and secondary females overlapped very little in the use of space. Hence, females mated to polygynous males may share parental care disproportionally but not territorial resources. Female attachment to territories and exclusive use of space together with male’s expansion of territories to achieve polygyny suggests that Southern House Wrens engage in sublease polygyny.