Contrasting associations between parental coordination and breeding success in albatrosses across differing...

Understanding how animals acquire resources and allocate them to reproduction is fundamental for identifying the factors shaping fitness. In species with biparental care, both the amount each parent invests and how well their efforts are coordinated can influence reproductive success. Yet the benefits of coordination are unlikely to be universal and instead may depend strongly on species' ecology and environmental context. Despite this, many studies still focus on one parent in isolation, overlooking the potential importance of joint investment strategies. Here, we examined how parental effort and coordination, measured here as the relative investment of both parents, influenced breeding success in black-browed Thalassarche melanophris and wandering albatrosses Diomedea exulans across colonies characterised by differing levels of environmental variability. We found that the influence of parental coordination on breeding success differed between species, breeding stages, and sites. Longer foraging trips improved annual breeding success during incubation for black-browed albatrosses, whereas the effect of longer trips during brooding varied between sites subject to differing environmental variability. Similarity in the predictability and duration of partners' foraging trips was associated with higher breeding success at sites with higher environmental stability in both species but had little effect where conditions were more variable. This suggests that patterns of reproductive investment may differ according to environmental context, potentially reflecting a shift toward individual flexibility in more unpredictable conditions. Our findings underscore the importance of considering both parents' contributions when linking reproductive strategies to breeding outcomes and highlight how observed differences in breeding success across colonies may reflect shifts in the trade-offs between self-maintenance and offspring investment within varying environmental contexts.