1. Non-consumptive predator effects have been shown to influence a wide range of behavioural, life history, and morphological traits. Extra-pair reproduction is widespread among socially monogamous birds and may incur predation costs. Consequently, altered rates of extra-pair reproduction are expected in circumstances characterized by increased adult perceived predation risk. 2. Additionally, extra-pair reproduction is expected to be most affected for birds with phenotypes that generally increase predation risk (such as more active individuals). 3. In two consecutive years, perceived predation risk was manipulated for great tits, Parus major breeding in 12 nest-box plots by broadcasting sounds of their main predator (European sparrowhawk Accipiter nisus; 6 plots). As a control treatment, sounds of a sympatric, avian non-predator species were broadcasted (Eurasian blackbird, Turdus merula; 6 plots). 4. Levels of extra-pair paternity did not differ between plots with different predation-risk treatments. Males that moved more in a novel environment (more active or ‘faster exploring’) tended to have offspring with fewer partners, but this effect did not vary with predation-risk treatment. 5. From an adaptive viewpoint, predation costs associated with extra-pair reproduction may be small and may not outweigh the benefits of extra-pair behaviour. Research on a broader range of taxa with different mating strategies is now needed to confirm the generality of our findings.

Optimal life-history decisions are shaped by prevailing environmental conditions. In the context of urbanization, environmental differences between urban and rural areas are known to vary across a multitude of axes. The relative roles of specific axes and whether they explain variation in avian life histories between forest and city populations have not often been studied empirically. This study comprehensively views urbanization from a multidimensional environmental perspective. For each of 13 nest box plots of a common passerine bird (the great tit Parus major), we quantified temperature, humidity, light, and noise, and subsequently assessed direct versus indirect effects of each environmental axis on components of annual reproductive success by applying a path analytical framework. All quantified environmental axes, and life-history traits, showed substantial repeatable variation between the plots. Forest and city plots differed tremendously in temperature, humidity, and light. We were able to attribute among-population variation in life history to variation in these environmental effects. However, the simple dichotomy between forest and city populations explained the data best. Birds in the city laid earlier, which indirectly resulted in smaller clutches, and their offspring fledged in poorer condition, compared to conspecifics in forests. Those differences persisted after controlling for temperature, humidity, light, and noise, which implies that they were shaped by other factors than the ones quantified in this study. In summary, our findings question the common interpretation that differences between forest and city areas relate to specific environmental axes that covary with urbanization, especially in in lieu of quantitative measurements.

Males of socially monogamous species can increase their siring success via within-pair and extra-pair fertilizations. In this study, we focused on the different sources of (co)variation between these siring routes, and asked how each contributes to total siring success. We quantified the fertilization routes to siring success, as well as behaviors that have been hypothesized to affect siring success, over a five-year period for a wild population of great tits Parus major. We considered siring success and its fertilization routes as “interactive phenotypes” arising from phenotypic contributions of both members of the social pair. We show that siring success is strongly affected by the fecundity of the social (female) partner. We also demonstrate that a strong positive correlation between extra-pair fertilization success and paternity loss likely constrains the evolution of these two routes. Moreover, we show that more explorative and aggressive males had less extra-pair fertilizations, whereas more explorative females laid larger clutches. This study thus demonstrates that (co)variation in siring routes is caused by multiple factors not necessarily related to characteristics of males. We thereby highlight the importance of acknowledging the multi-level structure of male fertilization routes when studying the evolution of male mating strategies.