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Behavioural traits are considered animal personality traits when individuals differ consistently in trait expression across time and context. Previous research has primarily focused on the shy-bold continuum, with research on sociability as potential proxy for animal personality traits only recently being considered. Here, we test the hypothesis that three node-based metrics derived from social association networks between individuals (strength, betweenness, closeness) can be considered proxies for animal personality traits in a passerine bird. Using experimental data from house sparrows in captive populations, and observational data from house sparrows in a wild population, we show that all three traits exhibit repeatability. The highest repeatability values were estimated in male-only captive groups, while repeatabilities estimated in single-sex networks subsets from mixed-sex groups showed no sex-specificity. We also show that changes in social group composition led to a decrease in repeatability for up to six months. Concluding, this work provides substantial and generalizable support for the notion that social network node-based traits map animal personalities.

There is no consensus yet on the reasons why females engage in extra-pair copulations (EPCs). In some species, females have been shown to accrue some indirect benefits, but these effects are not consistent across species and studies. The sexual conflict hypothesis posits that extra-pair paternity (EPP) is the result of strong selection for male pursuit of EPC without real benefits for females. In order to test this hypothesis, we experimentally reduced wing area (reversibly tying together some primary feathers), in a group of pied flycatcher females ( Ficedula hypoleuca ). The manipulation increases wing loading (body mass/wing area), which is negatively associated with flying ability, and thus with the capacity to escape from unwanted copulations. We compared the levels of EPP in this experimental group with those of a group of un-manipulated females. Experimental females almost doubled the proportion of extra-pair young (EPY) with respect to control females. In addition, more males sired EPY in experimental than in control broods containing EPY. These results suggest that in our study population, EPP could be partially a product of female capacity to avoid EPCs. We also discuss the alternative hypothesis that results might be due to an eventual reduction of female attractiveness.

As parental care is costly, it can be expected that there will be a sexual conflict between parents over the individual levels of parental investment because each parent has limited resources to invest in a reproductive event. Theoretical models of parental investment predict that when one parent reduces its parental effort, the other parent should adjust its effort facultatively to compensate for the decrease in the mate's contribution. Here, we tested for facultative adjustments in care in the rock sparrow, Petronia petronia. In this species, both sexes can desert the brood, creating the potential for strong sexual conflict over parental care to occur. To that end, we examined how rock sparrow parents adjust their level of care in response to an experimental mate removal for a limited time period, mimicking the starting phase of the desertion process. We compared male and female provisioning rates before and after an experimental mate removal. Males behaved according to the prediction of compensatory adjustment, as they allocated more care to the offspring and returned faster to the nest after female removal, whereas females showed no response. Our study shows sexual differences in response to mate removal in a species with biparental care and strong sexual conflict over parental care, and suggests that males may use the female absence to determine their actual parental effort. Significance statement Strong differences in parental care, with one sex providing more care than the other, are widespread across the animal kingdom. Theoretical models of parental investment predict that when one parent reduces its care, the mate should adjust its care facultatively to compensate. Here, we tested for facultative adjustments in care in the rock sparrow when their mates were experimentally removed for a limited time period. We show that only male behavior was consistent with theoretical predictions as they increased their frequency of provisioning significantly after mate removal, whereas females showed no response. Our study suggests that members of a pair do not make independent decisions, but negotiate to modify their effort in direct response to the prior effort of their mate.