Quantifying tradeoffs in accuracy and monitoring effort to support management decisions for low-density shorebird populations

Abstract

Inherent tradeoffs exist between survey effort and accuracy, with major implications for the design of effective monitoring programs as budgets and available resources influence both uncertainty and statistical power. Migratory shorebirds are experiencing population declines across their range; thus, effective monitoring is critical to understand drivers of migration chronologies, population dynamics, and biological response to restoration. In this study, we investigated how survey frequency may influence data uncertainty in migratory shorebird response to management actions at the Heʻeia National Estuarine Research Reserve (NERR), where stewards are interested in the long-term impacts of decisions that affect three species of shorebirds: ʻAkekeke (Arenaria interpres); Kōlea (Pluvialis fulva); and ʻŪlili (Tringa incana). We co-developed a high-effort monitoring protocol with site partners and modeled how well reduced survey frequencies captured occupancy dynamics and the variability in species counts observed under our full protocol. We found no difference in relative accuracy between surveys made once and twice a month, indicating that person-hours spent monitoring at this site could be halved without exceeding acceptable uncertainty thresholds for long-term management. Shorebirds varied in their habitat preferences, suggesting that individual species preferences should be considered when restoring or protecting habitat for a mixed assemblage. While ʻAkekeke and ʻŪlili used tidally limited habitat, Kōlea were observed to be wide generalists occurring throughout the reserve boundaries. This study provides a model for a relatively low-investment strategy to inform survey design for monitoring low-abundance or seasonally variable species of management interest.