Risk-taking behaviour relates to timing of breeding in a sub-Antarctic rainforest bird

Within-population variation in timing of breeding may be linked to a trade-off between the risks and benefits of breeding earlier. This trade-off may be mediated by individual risk-taking behaviour, but this needs to be assessed in detail in wild populations. Here, we recorded timing of breeding and risk-taking behaviour during three consecutive breeding seasons in a resident population of Thorn-tailed Rayadito Aphrastura spinicauda located in Navarino Island (55°S), southern Chile. Navarino is a high-latitude, highly seasonal continental island in southern Chile where early breeding may be risky for rayaditos, given the presence of low temperatures, storms and relatively low food abundance during early spring. We used novel environment tests to assess exploratory behaviour, which in turn was used as a proxy of risk-taking behaviour. In addition, we evaluated the potential consequences of timing of breeding and risk-taking behaviour on three measures of reproductive success: clutch size, number of fledglings produced and body condition of the offspring. We found that risk-prone individuals started breeding earlier than risk-averse individuals but we did not find evidence for an effect of timing of breeding on any of the variables of seasonal breeding success. However, we observed that fast-exploring females tended to lay smaller clutches. Measurements reflecting lifetime reproductive success may better reflect an effect of timing of breeding and risk-taking behaviour, but this needs to be studied. Our results support the idea that risk-taking behaviour is linked to early breeding in high-latitude environments. We suggest that, despite the risks that low temperatures and snowstorms pose to breeding rayaditos during early spring, it is possible that early breeders increase the probability of occupying better nesting cavities and they may adjust the timing of breeding to match brood provisioning with peak resource abundance.