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.

就田间努力和经济预算而言，对长寿和难以捉摸的物种进行监测的方案往往会付出高昂的代价，但往往将这两个组成部分分开考虑。另外，在基于环境因素的不完善检测条件下，使用可靠的可检测性估计值的信息很少，这对于准确估计财务成本和定义最佳监控策略至关重要。在这项研究中，我们使用了针对埃及秃Ne Neophron percnopterus的强化调查程序（2017–2018）Bizkaia（西班牙北部）的种群数量，以考虑到不完美的检测来模拟巢中的可检测性。我们的主要目标是估计调查的数量和时间，以及调查工作量/成本的分配，以便设计具有成本效益的监控程序。首先，在整个繁殖季节，我们对历史上被研究物种占据的19个嵌套领土使用了集中采样方法。然后，我们采用了单季节占用模型来评估可检测性，其中考虑了每个窝处不同级别的工作量（从1到5小时），包括物种育种物候和可以改变检测概率的环境协变量。我们的研究结果表明，该物种在干旱年份更容易被发现，并且在筑巢期可见巢穴时，投入了五个小时的调查时间。单个巢中占95％假阴性的最佳监视天数是8天，每个繁殖阶段投入一小时。在可见巢穴的干旱年份达到最佳监测成本，每个繁殖阶段投资一小时（ca. 242€/巢）。在雨季，巢不可见，监测成本最高（约1954€/巢）。在不考虑协变量的情况下监控整个被占领的嵌套领土的成本为23,294欧元（n = 19）。为了提供可靠的物种评估，进行严格的调查并准确估算监测成本，研究应考虑到不完善的检测，尤其是对于长寿脊椎动物。在这里，我们表明，监测计划应（a）考虑到检测物种所需的工作量，同时考虑了特定物种的繁殖生态，以及（b）根据较低的成本和环境条件调整现场工作量。我们的研究结果为有效分配人力和经济资源提供了简单实用的指导方针，这些对参与定期监测可疑物种的从业人员可能会感兴趣。