Individual consumption of supplemental food as a predictor of reproductive performance and viral infection intensity

1. Supplemental food is often provided to threatened species in order to maintain or enhance reproductive fitness and thus population growth. However, its impact on individual reproductive fitness is rarely evaluated, despite being associated with both positive and negative consequences. 2. We used stable isotope analyses to characterise the relative proportional consumption of supplemental food and quantitative polymerase chain reaction to assess beak and feather disease viral infection intensity among parakeets. Life-history and nest-site data from a long-term monitoring effort was incorporated. 3. Older females benefitted the most from supplemental feeding; demonstrated by a greater reproductive uplift than younger females. There were no strong predictors of viral infection levels among nestlings. 4. Reproductive fitness, measured by the number of fledglings produced per brood, was positively associated with proportional dietary content of supplemental food among adult parakeets and breeding pairs that nested closer to feeding stations consumed more supplemental food than those nesting further away. 5. Synthesis and applications. Our study demonstrates that supplementary feeding can lead to an overall increase in population growth. However, by characterising individual consumption, we also reveal subtle patterns of use and differential benefits on reproductive fitness within a population. Manipulating the delivery of supplemental food may help to reduce demand on finite resources or target the proportion of a population that derives the most benefit, but is associated with trade-offs in fecundity. For example, the use of and access to feeding stations could potentially be targeted towards specific individuals, or positioned in the habitats most deficient in native food. However, increasing reproductive fitness in one component of the population may be accompanied by a decrease in another. This knowledge can be incorporated into adaptive management strategies that aim to fulfil specific objectives associated with species recovery and long-term viability as long as the relative importance of each objective is be considered