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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. [ABSTRACT FROM AUTHOR]

1. A population's effective size (Ne) is a key parameter that shapes rates of inbreeding and loss of genetic diversity, thereby influencing evolutionary processes and population viability. However, estimating Ne and identifying key demographic mechanisms that underlie the Ne to census population size (N) ratio, remains challenging, especially for small populations with overlapping generations and substantial environmental and demographic stochasticity and hence dynamic age-structure. 2. A sophisticated demographic method of estimating Ne/N, which uses Fisher's reproductive value to account for dynamic age-structure, has been formulated. However, this method requires detailed individual and population-level data on sex and age-specific reproduction and survival and has rarely been implemented. 3. Here, we use the reproductive value method and detailed demographic data to estimate Ne/N for a small and apparently isolated red-billed chough (Pyrrhocorax pyrrhocorax) population of high conservation concern. We additionally calculated two single-sample molecular genetic estimates of Ne to corroborate the demographic estimate and examine evidence for unobserved immigration and gene flow. 4. The demographic estimate of Ne/N was 0.21, reflecting a high total demographic variance (σ 2 dg) of 0.71. Females and males made similar overall contributions to σ 2 dg. However, contributions varied among sex-age classes, with greater contributions from 3 year-old females than males, but greater contributions from ⩾5 year-old males than females. 5. The demographic estimate of Ne was ∼30, suggesting that rates of increase of inbreeding and loss of genetic variation per generation will be relatively high. Molecular genetic estimates of Ne computed from linkage disequilibrium and approximate Bayesian computation were approximately 50 and 30, respectively, providing no evidence of substantial unobserved immigration which could bias demographic estimates of Ne. 6. Our analyses identify key sex-age classes contributing to demographic variance and thus decreasing Ne/N in a small age-structured population inhabiting a variable environment. They thereby demonstrate how assessments of Ne can incorporate stochastic sex and age-specific demography and elucidate key demographic processes affecting a population's evolutionary trajectory and viability. Furthermore, our analyses show that Ne for the focal chough population is critically small, implying that management to re-establish genetic connectivity may be required to ensure population viability. [ABSTRACT FROM AUTHOR]

Determining the precise timing and location of major demographic bottlenecks, such as periods of low survival, is key to identifying ecological causes of variation in population growth rate. Such understanding is key to designing efficient and effective mitigation. In a protected population of red-billed chough Pyrrhocorax pyrrhocorax on Islay, Scotland, variation in population growth rate largely reflects among-year variation in first-year survival. First-year survival was unprecedentedly low during 2007-2010, threatening population viability. We used colour-ring resightings to estimate monthly survival probabilities (Φ) throughout the first year from fledging for eight chough cohorts (totalling 519 individuals) representing the full observed range of variation in first-year survival. We thereby identify the time and location of recent low survival. On average across all cohorts, Φ varied among months, being low during the first month after ringing (May-June, accounting for c. 24% of all first-year mortality) and high during the last 4 months of the first year (January-May, accounting for c. 6% of all first-year mortality). Most mortality ( c. 70%) occurred after fledglings dispersed from natal territories. The 2007-2009 cohorts experienced low Φ during July-December. This represents an additional low survival period compared to previous cohorts rather than decreased Φ across all months or further decreases through periods when Φ was low across all cohorts. Synthesis and applications. These data have general relevance in showing that dramatically low annual survival, which needs to spark rapid management action, can reflect different and unanticipated periods of low survival rather than exaggeration of typical variation. With specific regard to conserving Islay's chough population, our data show that sub-adult survival has recently been low during July-December, probably reflecting conditions on key grassland foraging areas. Managers aiming to increase population viability should increase invertebrate diversity, abundance and availability at these times and locations, thereby increasing foraging options available to choughs. [ABSTRACT FROM AUTHOR]

1. Understanding the degree to which reproductive success varies with an individual’s age and lifespan, and the degree to which population-level variation mirrors individual-level variation, is central to understanding life-history evolution and the dynamics of age-structured populations. We quantified variation in the survival probability of offspring, one key component of reproductive success and fitness, in relation to parent age and lifespan in a wild population of red-billed choughs ( Pyrrhocorax pyrrhocorax). 2. On average across the study population, the first-year survival probability of offspring decreased with increasing parent age and lifespan; offspring of old parents were less likely to survive than offspring of young parents, and offspring of long-lived parents were less likely to survive than offspring of short-lived parents. 3. However, survival did not vary with parent age across offspring produced by groups of parents that ultimately had similar lifespans. 4. Rather, across offspring produced by young parents, offspring survival decreased with increasing parent lifespan; parents that ultimately had long lifespans produced offspring that survived poorly, even when these parents were breeding at young ages. 5. The average decrease in offspring survival with increasing parent age observed across the population therefore reflected the gradual disappearance of short-lived parents that produced offspring that survived well, not age-specific variation in offspring survival within individual parents. 6. The negative correlation between offspring survival and maternal lifespan was strongest when environmental conditions meant that offspring survival was low across the population. 7. These data suggest an environment-dependent trade-off between parent and offspring survival, show consistent individual variation in the resolution of this trade-off that is set early in a parent’s life, and demonstrate that such structured life-history variation can generate spurious evidence of senescence in key fitness components when measured across a population. [ABSTRACT FROM AUTHOR]