6533b7dcfe1ef96bd1272840

RESEARCH PRODUCT

Applying economic and ecological criteria to design cost-effective monitoring for elusive species

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Abstract Monitoring programs of long-lived and elusive species often incur high costs in terms of field effort and economical budget, but both components are often considered separately. Also, there is scant information on the use of reliable detectability estimates under imperfect detection conditions based on environmental factors, which is key to accurately estimate financial costs and define optimum monitoring strategies. In this study, we use an intensive survey program (2017–2018) of the Egyptian vulture Neophron percnopterus population in Bizkaia (northern Spain) to model detectability at nests taking into account imperfect detection. Our main goal is to estimate both the number and timing of surveys, and the allocation of survey effort/costs, in order to design cost-effective monitoring programs. Firstly, throughout the breeding seasons, we used focal sampling methods on 19 nesting territories historically occupied by the study species. Then, we employed single-season occupancy models to assess detectability considering different levels of effort (from 1 to 5 h) at each nest, including both species breeding phenology and environmental covariates that could modify detection probabilities. Our results showed that the species was more likely to be detected in dry years and when the nest was visible during the nestling period, investing five hours of the survey. The optimal number of monitoring days required to account for 95% of false negatives for a single nest was eight days, investing one hour per breeding stage. The optimal monitoring cost was reached in dry years when the nest was visible, investing one hour per breeding stage (ca. 242 €/nest). The cost of monitoring was highest in rainy years when the nest was not visible (ca. 1954 €/nest). The cost of monitoring entire occupied nesting territories without accounting for covariates was of 23,294 € (n = 19). In order to offer reliable species assessments, design rigorous surveys and accurately estimate monitoring costs, studies should account for imperfect detection, particularly for long-lived vertebrates. Here, we show that monitoring programs ought to (a) consider the effort necessary to detect the species while accounting for species-specific breeding ecology and, (b) adjust field effort based on lower costs and environmental conditions. Our results provide simple and practical guidelines for the efficient allocation of human and economic resources, which could be of interest to those practitioners involved in the regular monitoring of elusive species.