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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. © 2011 Dt. Ornithologen-Gesellschaft e.V.

Fernandez G.J.,University of Buenos Aires | Corral M.G.,University of Buenos Aires | Llambias P.E.,Ecologia del Comportamiento Animal
Acta Ethologica | Year: 2013

When faced with a predator near the nest, breeding birds faced a dilemma: to continue providing parental care to their offspring exposing themselves to risk or to desert the nest for a brief period of time, exposing their offspring to harm due to the suspension of parental brooding and feeding. In this study, we analysed the response of nesting Southern house wrens (Troglodytes aedon musculus) to a predator model placed near the nest. The experiment was performed in 56 nests when nestling were 3-4 or 10-12 days old. The model (a plastic decoy of the Great Horned Owl Bubo virginianus) was placed at 3 m from the nest. Parent risk-taking was measured as the time elapsed for males and females to resume parental activities during the exposition to the model. We found that males and females delayed parental visits when exposed to the predator model, but females resumed them faster than males, irrespectively of the nesting stage. We also found that males refused to enter to the nest more frequently than females when exposed to the predator model. No effect of breeding experience or nesting stages was noted in the risk taking behaviour of adults. We suggest that sexual differences detected in this species reflect the higher ability of females to cope with the nestling needs and its lower lifetime expectancy. © 2013 Springer-Verlag Berlin Heidelberg and ISPA.

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