Survey design for broad-scale, territory-based occupancy monitoring of a raptor: Ferruginous hawk (Buteo regalis) as a case study

Abstract

Given the uncertain population status of low-density, widely-occurring raptors, monitoring changes in abundance and distribution is critical to conserving populations. Nest-based monitoring is a common, useful approach, but the difficulty and expense of monitoring raptor nests and importance of reliable trend data to conservation requires that limited resources are allocated efficiently. Power analyses offer a helpful tool to ensure that monitoring programs have the ability to detect trends and to optimize financial resources devoted to monitoring. We evaluated alternative monitoring designs for raptors to identify appropriate survey effort to detect population trends. We used data collected from a territory-occupancy study of ferruginous hawks throughout Wyoming to guide simulations and evaluate the ability to detect trends in occupancy rates. Results suggest that greater gains in precision of trend estimation may be achieved through the addition of more sites and not more visits; statistical power was ≥80% when monitoring lasted 20 years and population declines were 20%; and probability of detection affected statistical power less than rates of population decline. Monitoring at least 150 sites for 20 years would provide reasonable estimates of trend in occupancy given certain rates of detection and occupancy, but only for population declines of 20%. Removal sampling did not result in substantial changes of any metrics used to evaluate simulations, providing little justification for employing the standard design if territory occupancy is the variable of interest. Initial rates of territory occupancy may be biased high, a problem inherent to many studies that monitor territory occupancy. We explored the effects of lower rates of initial occupancy on the ability to detect trends. Although we present data from a study of ferruginous hawks, our simulations can be applied to other raptor species with similar life history and population dynamics to provide guidance for future trend estimation of territory occupancy.

Imperfect detection alters the outcome of management strategies for protected areas

“…The negative consequences of insufficient sampling and/or an inappropriate protocol become more apparent with respect to predator detection. Due to their lower population densities and wide ranges, predators may require either more search effort, or the importance of correct monitoring protocols may be increased (Johnson et al ). In the present study when search effort is 0.1–10 mL, both a small to large protocol and a large to small protocol always produce incorrect results (i.e.…”

Using GPS tracking to monitor the breeding performance of a low-density raptor improves accuracy, and reduces long-term financial and carbon costs

“…Raptor species have shown some of the largest declines among avian species, and globally at least 50% of raptor species have declining populations [11]. While migratory, colonial or other spatially grouped species can be monitored via annual counts [12][13][14], monitoring of non-migratory, territorial raptors is usually only effective via nest site monitoring [15] and this presents unique challenges for species which occur at low densities or within regions where lack of infrastructure (e.g. roads) may compromise monitoring efficiency [10].…”

Power to the people: Analysis of occupancy models informed by local knowledge

“…To address this issue, Guillera‐Arroita and Lahoz‐Monfort (2012) developed and tested a formula for power analysis which accounts for both occupancy and detection probabilities. Studies have since found this approach to be effective in assessing the power of different occupancy study designs (Barata et al, 2017; Johnson et al, 2019).…”