Using Decision Science for Monitoring Threatened Western Snowy Plovers to Inform Recovery

SIMPLE SUMMARY: We developed a decision-analysis evaluation of a suite of nine alternative strategies for monitoring federally Threatened populations of Western Snowy Plovers (Charadrius nivosus nivosus) along the Pacific Coast, US. The species is increasing in numbers as a result of successful recovery plan implementation efforts, and is no longer feasible to conduct absolute censuses of birds and nests, as well as track productivity, fate, and predation events at every nest. What is needed is a statistically sound and economically feasible sampling approach to continue monitoring plover populations and informing management decisions that advance recovery for the species. We convened an eight-person technical team of plover monitoring experts to score the nine alternative strategies on a set of six categories of monitoring objectives such as maximizing the accuracy of determining the adult population size. Scoring consisted of ordinal scales of performance measures related to the recovery criteria for the species, and to other criteria related to monitoring reporting. We calculated overall scores among the team members, and explored how different objective weights influenced which monitoring strategies were best. Several monitoring strategies stood out as having the highest utility, depending on the importance given to cost, which we subsequently conveyed to the US Fish and Wildlife Service, responsible for monitoring as well as for consideration when choosing a standard monitoring sampling strategy throughout all the plover recovery units. ABSTRACT: Western Snowy Plovers (Charadrius nivosus nivosus) are federally listed under the US Endangered Species Act as Threatened. They occur along the US Pacific coastline and are threatened by habitat loss and destruction and excessive levels of predation and human disturbance. Populations have been monitored since the 1970s for distribution, reproduction, and survival. Since the species was federally listed in 1993 and a recovery plan was approved under the US Fish and Wildlife Service in 2007, recovery actions have resulted in growing populations with increased presence at breeding and wintering sites throughout their Pacific Coast range. This success has created logistical challenges related to monitoring a recovering species and a need for identifying and instituting the best monitoring approach given recovery goals, budgets, and the likelihood of monitoring success. We devised and implemented a structured decision analysis to evaluate nine alternative monitoring strategies. The analysis included inviting plover biologists involved in monitoring to score each strategy according to a suite of performance measures. Using multi-attribute utility theory, we combined scores across the performance measures for each monitoring strategy, and applied weighted utility values to show the implications of tradeoffs and find optimal decisions. We evaluated four scenarios for weighting the monitoring objectives and how risk attitude affects optimal decisions. This resulted in identifying six strategies that best meet recovery needs and were Pareto optimal for cost-effective monitoring. Results were presented to the US Fish and Wildlife Service, responsible for monitoring as well as for consideration to ensure consistent monitoring methods across the species’ range. Our use of structured decision-making can be applied to cases of other species once imperiled but now on the road to recovery.