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Conceptual and methodological advances in population and evolutionary ecology are often pursued with the ambition that they will help identify demographic, ecological and genetic constraints on population growth rate (λ), and ultimately facilitate evidence‐based conservation. However, such advances are often decoupled from conservation practice, impeding translation of scientific understanding into effective conservation and of conservation‐motivated research into wider conceptual understanding. We summarise key outcomes from long‐term studies of a red‐billed chough Pyrrhocorax pyrrhocorax population of conservation concern, where we proactively aimed to achieve the dual and interacting objectives of advancing population and evolutionary ecology and advancing effective conservation. Estimation of means, variances and covariances in key vital rates from individual‐based demographic data identified temporal and spatial variation in subadult survival as key constraints on λ, and simultaneously provided new insights into how vital rates can vary as functions of demographic structure, natal conditions and parental life history. Targeted analyses showed that first‐year survival increased with prey abundance, implying that food limitation may constrain λ. First‐year survival then decreased dramatically, threatening population viability and prompting emergency supplementary feeding interventions. Detailed evaluations suggested that the interventions successfully increased first‐year survival in some years and additionally increased adult survival and successful reproduction, thereby feeding back to inform intervention refinements and understanding of complex ecological constraints on λ. Genetic analyses revealed novel evidence of expression of a lethal recessive allele, and demonstrated how critically small effective population size can arise, thereby increasing inbreeding and loss of genetic variation. Population viability analyses parameterised with all available demographic and genetic data showed how ecological and genetic constraints can interact to limit population viability, and identified ecological management as of primacy over genetic management to ensure short‐term persistence of the focal population. This case study demonstrates a full iteration through the sequence of primary science, evidence‐based intervention, quantitative evaluation and feedback that is advocated in conservation science but still infrequently achieved. It thereby illustrates how pure science advances informed conservation actions to ensure the (short‐term) stability of the target population, and how conservation‐motivated analyses fed back to advance fundamental understanding of population processes.

Overall impacts of targeted conservation interventions on population growth rate (λ) will depend on within‐year and among‐year variation in exposure of target individuals to interventions, and in intervention efficacy in increasing vital rates of exposed individuals. Juvenile survival is one key vital rate that commonly varies substantially within and among years, and consequently drives variation in λ. However, within‐year, among‐year and overall impacts of targeted interventions on population‐wide survival probabilities of potentially mobile juveniles are rarely quantified, precluding full evaluation and evidence‐based refinement of interventions. We applied multi‐state mark–recapture models to 8 years of ring–resighting data from a threatened red‐billed chough Pyrrhocorax pyrrhocorax population to quantify within‐year and among‐year variation in juvenile exposure to a targeted intervention of supplementary feeding and parasite treatment, and to estimate efficacy in increasing juvenile survival probability. We then combined and up‐scaled these estimated effects to evaluate the impact of the 8‐year intervention on overall population‐wide survival probability and resulting population size. High proportions of surviving juveniles (>70%) were exposed to the intervention across the annual biological cycle in all years. Exposure was associated with higher short‐term survival probabilities through the full annual cycle. Consequently, management increased estimated population‐wide annual juvenile survival by approximately 0.14. However, such effects were only evident in cohorts with low overall annual survival. Population models projected that these impacts on annual juvenile survival substantially reduced population decline, such that population size at the end of the 8‐year intervention was approximately double that without management. Synthesis and applications. Our results show how complex patterns of within‐year and among‐year variation in exposure and efficacy of targeted conservation interventions can arise and scale up to affect population‐level outcomes. We demonstrate overall positive effects of a joint supplementary feeding and parasite treatment intervention on the focal chough population, but also highlight potential routes to improve efficacy, for example, through more precise targeting of interventions and agricultural management actions in the context of among‐year variation in environmental conditions.