Adult sex ratio in south temperate house wrens is explained by sexual differences in adult survival

CARRO, MARIANA E.; FERNÁNDEZ, GUSTAVO J.; MAHLER, BETTINA

Journal of Ornithology

Springer Science and Business Media Deutschland GmbH

Año: 2023

2193-7192

Skewed adult sex ratio (ASR) has been proposed to be a consequence of breeding individuals producing a biassed primary sex ratio, sexual differences in offspring mortality or juvenile dispersal, or sexual differences in adult mortality. In this study, we analysed if a skewed primary sex ratio, sexual differences in recruitment and/or sexual differences in adult survival were responsible for the sustained male-skewed ASR in a south temperate population of house wrens (Troglodytes aedon bonariae). Molecular sex determination of 229 nestlings raised from 56 nests during two consecutive breeding seasons showed that primary sex ratio did not depart significantly from equality. Also, although females are the dispersing sex, differences in the number of males and females recruited into the population did not explain the skewed ASR. Finally, survival analysis of marked and re-sighted breeding individuals using a 2004–2017 database revealed that males had a significant higher survival probability than females (overall annual survival probability: 0.53 vs. 0.34, respectively), and explained a high amount of variance in the inter-annual ASR variation. As adult individuals showed a high philopatry to their breeding territories both within and amongst breeding seasons and we never found any marked individual of our study site in the neighbouring populations, we suggest that the skewed ASR observed in this population can be mainly attributed to sexual differences in adult survival.