Within-season increase in parental investment in a long-lived bird species: investment shifts to maximise successful reproduction? 2 Running title: within-season investment in long-lived bird 4

In nest-building species predation of nest contents is a main cause of reproductive failure and 16 parents have to trade off reproductive investment against antipredatory behaviours. While this trade-off is modified by lifespan (short-lived species prioritise current reproduction, long-lived 18 species prioritise future reproduction), it may vary within a breeding season, but this idea has only been tested in short-lived species. Yet, life-history theory does not make any prediction how long20 lived species should trade-off current against future reproductive investment within a season. Here, we investigated this trade-off through predator-exposure experiments in a long-lived bird species, 22 the brown thornbill. We exposed breeding pairs that had no prior within-season reproductive success to the models of a nest predator and a predator of adults during their first or second 24 breeding attempt. Overall, parents reduced their feeding rate in presence of a predator, but parents feeding second broods were more risk sensitive and almost ceased feeding when exposed to both 26 types of predators. However, during second breeding attempts, parents had larger clutches and a higher feeding rate in absence of predators than during first breeding attempts, and approached 28 both types of predators closer when mobbing. Our results suggest that the trade-off between reproductive investment and risk-taking can change in a long-lived species within a breeding season 30 depending on both prior nest predation and renesting opportunities. These patterns correspond to those in short-lived species, raising the question of whether a within-season shift in reproductive 32 investment trade-offs is independent of lifespan. 34