Expensive active management programs are increasing worldwide, while resources for conservation remain scarce. There is a need to evaluate management actions, so that scarce resources are used more cost-effectively. We evaluate the effectiveness of alternative protection measures for Montagu's harrier nests in Spanish farmlands. The species is focus of extensive protection measures across Europe owing to high rates of nest destruction during mechanical harvesting operations. We use a novel approach, combining Latin hypercube sampling and population viability analysis in order to explore the impact of alternative protection measures on populations' persistence across a whole range of resource allocation scenarios. We also report estimates of financial costs for different protection measures. Our results show that, in absence of nest protection, Spanish harrier populations would most likely decrease during the next 20 years. The most cost-effective protection measures, among those evaluated, were the relocation or removal of the chicks and harvest delay, although this varied according to region and context. Interestingly, retention of a small un-harvested buffer around the nest, despite being widely implemented across Spain, was less cost-effective than the other two protection measures. Overall, the cost-effectiveness of each protection measure varied widely by region and by local agronomic context. We ultimately explore what proportion of nests could be protected with the most effective measure in each studied region, and estimate how much this effort would cost to local administrations. This is a clear example of conservation science producing outcomes relevant to action. (C) 2014 Elsevier Ltd. All rights reserved.